final report de-mystifying the use of pas100 compost in ... media technical...final report...

Final Report

De-mystifying the use of PAS100

compost in horticultural growing

media

Project code: OMK005-002 Date: March 2014 Research date: December ‘12 – March ‘13

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(2013) De-mystifying the use of PAS100 compost in horticultural growing media. (WRAP)

Project OMK005-002) Litterick, AM.; Holmes, S.; Daly, M.; Becvar, A. and Wood, M.,

Earthcare Technical Ltd. Document reference: [e.g. WRAP, 2006, Report Name (WRAP Project TYR009-19. Report prepared by…..Banbury, WRAP]

Written by: Audrey Litterick, Susie Holmes, Mike Daly, Anna Becvar and Martin Wood Earthcare Technical Ltd.

Front cover photography: Healthy plants grown in compost based growing media at Golden Acre Nursery in Dorset

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De-mystifying the use of PAS100 compost in horticultural growing media 1

Executive summary

The Sustainable Growing Media Task Force (SGMTF) was established in 2011 and initially aimed to explore how to overcome barriers to further reducing peat use in horticulture. It has since adjusted its remit to that of putting the horticultural sector on a long-term sustainable footing by ensuring that all choices of growing media (or substrate) used for amateur gardening and professional horticulture are sustainable. It concluded that green compost will play an important role in sustainable growing media manufacture but that further work is required in order to improve confidence in using compost for this purpose. This project examined nine key issues reported by the SGMTF as representing barriers to increased use of composts as components of growing media. Evidence was gathered from scientific literature, relevant guidance/product specifications and from interviews with stakeholders including seven compost producers (of whom six also produced growing media), an additional three growing media manufacturers, eight growers and two growing media retailers. The extent to which each of the nine issues have been resolved was discussed and recommendations were made as to how to further improve PAS100 composts intended for use in growing media and increase sales and use of compost-included growing media (CIGM) in amateur and professional horticulture. One question not addressed in this report is that of the potential contamination of composts by herbicide residues. This has been considered in other research, and changes to published WRAP guidance on the production of composts for use in growing media have been made. Conclusions on the nine issues under study

Physical contamination: technical solutions are available to address this concern

effectively, though around one third of all of the stakeholders contacted believed that the

issue had not yet been effectively resolved and that it limited or prevented their use of

composts or CIGM;

High bulk density: technical solutions are available to help address this concern. Some

stakeholders felt that they had resolved the issue satisfactorily and that it was possible to

make good CIGM with sufficiently low bulk density. Others felt that it remained a concern

and that it limited or prevented their use of composts or CIGM;

High pH: technical solutions can partially address this concern and some evidence

suggests that high pH in non-peat growing media may be less of a concern than originally

thought. However, all of the growers and one of the two growing media retailers felt that

the issue had not yet been effectively resolved and that it limited or prevented their use

of composts or CIGM;

High electrical conductivity (EC): technical solutions can partially address this concern and

the majority of compost producers and growing media manufacturers believed that it had

never been a problem or that if managed with care, it merely limited the inclusion rates of

compost in growing media. All growers and one of the two growing media retailers felt

this issue had not yet been resolved and that it limited or prevented their purchase/use of

CIGM;

Weed seeds: technical solutions are available to address this concern and most compost

producers and growing media manufacturers believed that it had never been an issue for

them. However, one fifth of compost producers and growing media manufacturers, half of

the growers and one of the two growing media retailers felt that the issue had not yet

been effectively resolved and that it limited or prevented their use of composts or CIGM;


Sciarid flies and other pests: limited technical solutions are available to address this

concern at present and there is still some concern amongst stakeholders on the subject.

Around half of stakeholders felt that the issue affected them. For example, it limited the

use of compost in growing media by growing media manufacturers and it limited sales of

CIGM to amateur gardeners and professional growers;

Shelf life: technical solutions are available to address this concern. Most compost

producers and growing media manufacturers believed that the issue had never been of

concern or had been resolved, whereas most of the growers and both growing media

retailers felt that the issue had not been effectively resolved and that it limited or

prevented their use of composts or CIGM;

Consistency: technical solutions are available to address this concern. Half of the compost

producers and growing media manufacturers believed that the issue had never been of

concern or had been resolved whereas the remaining half, along with all of the growers

and both retailers felt that the issue affected them. Half of the compost producers and

growing media manufacturers consulted felt that it limited their sales or use of compost in

growing media. Retailers felt that it limited their purchase of CIGM and growers felt that it

limited their use of CIGM; and

Human pathogens: technical solutions are available to address this concern effectively

(although more information may be required on the incidence of Legionella species

bacteria if further outbreaks of Legionnaire’s disease are associated with growing media).

Half of the compost producers and growing media manufacturers believed that the issue

had either never been of concern or had been adequately resolved but the remaining

compost producers and growing media manufacturers, most growers and one of the two

growing media retailers felt that the issue had not been effectively resolved and that it

limited or prevented their use of composts or CIGM.

Comments on information gathered It became clear through the assessment of information gathered from the literature review and stakeholder interviews that most of the issues have been wholly or partly resolved, particularly in the opinions of some of the compost producers who also manufacture growing media. Effective management of the issues requires an in-depth knowledge of the composting process and methods of maximising compost quality and also requires investment of time and money to achieve. It was also clear that several of the issues are perceived rather than real in the eyes of some stakeholders. The fact that many of the issues under study are still perceived to represent problems to some is compounded by the fact that many of the perceptions which stakeholders have relate to experiences from several years ago. There is a need to ensure that they understand the great improvements in compost quality which have been made in recent years. Some of them have considered using or have used composts in the past which were not even PAS100-accredited. This falls a long way short of material produced according to any specification at all, let alone a higher specification specifically designed for compost to be used in growing media (e.g. WRAP, 2011a). Some leading industry players have formed very poor opinions of composts which are evidently deeply ingrained. There is a clear need to show stakeholders just how consistent good composts can be, and that the economics of producing such compost means the right price must be paid to the composter. There is also a need to show stakeholders how to achieve and specify the required quality. The WRAP Guidelines and Specification (WRAP 2011a and b) go some way towards helping achieve this, but they need to be updated and promoted to ensure that all who might benefit from using them are aware of them.


Recommendations for research, demonstration and knowledge exchange The following work is recommended in order to address the outstanding issues of concern identified in this project, to increase production of top quality composts suitable for use in growing media, to increase the use of composts in growing media and to encourage sales and use of CIGM in amateur and professional horticulture. The full report indicates which recommendations relate particularly to the different stakeholder groups. It also shows how the proposed work relates to the findings of the project and how it will help to meet the project’s aims. The recommended work includes:

Study the effect of composting site management practices on compost consistency;

Comparison of Dutch and UK quality composts – can lessons be learnt from the Dutch

RHP system which is one of the few examples of a scheme which appears to have gained

confidence with the professional horticulture industry?;

Replicated experimental trials including:

work to demonstrate that the higher pH values found in CIGM as opposed to traditional

peat media do not necessarily cause problems

development of methods to prevent and control sciarid (and other) flies in both

amateur and professional situations; and

Nursery-based comparison trials and demonstration of best practice.

In addition to the above:

Additional work to improve knowledge of the benefits which composts can bring to

growing media was recommended, including studies on disease suppression and nutrient

management. If CIGM can be shown to be cheaper or better than alternative media, then

growers will be more likely to try it (or try it again)

The following priorities for knowledge exchange were identified in order to promote the

use of composts in growing media:

development of new or revised template documents (along the lines of those produced

by ORG and REAL to provide guidance to help producers consistently achieve the

required standards) and updated versions of the WRAP guides (‘Guidelines for the

specification of quality compost for use in growing media’, WRAP, 2011a and ‘Compost

production for use in growing media – a good practice guide’, WRAP, 2011b);

promotion of new and existing information relevant to increasing the use of quality

composts in growing media at trade shows and in the trade press;

tailor-made training courses/presentations; and

demonstration days/grower walks.


Contents

1.0 Introduction ................................................................................................. 8 1.1 Project background .................................................................................... 8 1.2 Benefits of using composts in growing media ............................................. 11 1.3 Project rationale and aims......................................................................... 12

2.0 Methodology ............................................................................................... 13 2.1 Interviews of industry stakeholders ........................................................... 13 2.2 Desk-based investigation .......................................................................... 13 2.3 Hyperlinked summary of UK legislation and good practice guidance.............. 14 2.4 Gap analysis to determine where additional research is required .................. 14 2.5 Proposal of knowledge exchange (KE) mechanisms ..................................... 15

3.0 Results and discussion ............................................................................... 15 3.1 Interviews of selected industry stakeholders ............................................... 15

3.1.1 Summary of stakeholder views ........................................................ 15 3.2 Desk-based investigation .......................................................................... 16

3.2.1 Physical contamination ................................................................... 16 3.2.2 High bulk density ........................................................................... 20 3.2.3 High pH ........................................................................................ 23 3.2.4 High electrical conductivity.............................................................. 25 3.2.5 Weed seeds ................................................................................... 26 3.2.6 Sciarid flies and other pests ............................................................ 29 3.2.7 Compost shelf life .......................................................................... 31 3.2.8 Compost consistency ...................................................................... 34 3.2.9 Microbiological safety ..................................................................... 40

3.3 Hyperlinked summary of UK legislation and good practice guidance.............. 44 3.3.1 The UK Compost Certification Scheme and BSI PAS100:2011 ............. 44 3.3.2 The Quality Protocol for Compost .................................................... 45 3.3.3 The Animal By-Products Regulations ................................................ 45 3.3.4 Guidelines for the specification of Quality Compost used in growing media (2011) ........................................................................................... 45 3.3.5 Compost production for use in growing media – A good practice guide (2011) 46 3.3.6 Microbiological safety of pot-grown fresh herbs ................................ 46

3.4 Gap analysis to determine where additional research and development is required ............................................................................................................ 46 3.5 Proposal for knowledge exchange (KE) mechanisms ................................... 49

4.0 Conclusions and recommendations ............................................................ 52 4.1 General points ......................................................................................... 52 4.2 Compost producers .................................................................................. 53 4.3 Growing media manufacturers ................................................................... 55 4.4 Growers .................................................................................................. 55 4.5 Retailers of growing media........................................................................ 56

5.0 References .................................................................................................. 57 A.1.1 BSI PAS100 compost producers and growing media manufacturers...... 63 A.1.2 Growers who may use growing media containing PAS100 compost ...... 69 A.1.3 Retailers’ perception ........................................................................ 73


Glossary

Aeration – The process by which oxygen-rich air is supplied to compost to replace air depleted of oxygen. Aerobic – Metabolic process that requires oxygen. Ammonia (NH3) – A gaseous compound composed of nitrogen and hydrogen, with a pungent odour. Anaerobic – Metabolic process occurring in the absence of oxygen. Animal By-Products Regulations – A set of European regulations designed to ensure food safety under the ‘farm to table’ approach set out in the EU White Paper on Food Safety adopted in January 2000. They contain strict animal and public health rules for the collection, transport, storage, handling, processing and use or disposal of all animal by-products (ABPs). Bacteria – A group of micro-organisms with a primitive cellular structure, in which the genetic material is not retained within an internal membrane (nucleus). Biodegradable – can be broken down through biological processes. BSI PAS100:2010 – A publicly available specification which covers the entire production process for composts and ensures that composts are quality assured, traceable, safe and reliable. Bulk density – The mass per unit volume of materials. Carbon dioxide - a colourless, odourless, tasteless gas that is produced as a result of respiration (by plants and animals including microorganisms). CGW (composted green waste) – a term often used by growing media manufacturers for green PAS100 compost. CIGM (compost-included growing media) – growing media which contain green and/or green/food compost. Compost - a stable, sanitised, soil-like material, which has been made through mixing, self-generated heating and aeration. Compost quality protocol – A standard which describes parameters for the full recovery of compost in England and Wales which provides user confidence, protects the environment and eases the regulatory burden on compost producers. It is not applicable in Scotland. Composting – The natural breakdown of biodegradable materials through mixing, self-generated heating and aeration to form a stable, soil-like material. Density – The weight or mass of a substance per unit of volume. Ericaceous – Plants belonging to the family Ericaceae including rhododendrons and heaths and heathers. This family of plants prefers to grow in acid soils or growing media and in this respect, they differ from most other common commercially grown plant families.


Feedstock – The biodegradable materials present at the start of a composting process. Green waste – Grass cuttings, leaves and prunings, from parks or gardens. Growing medium – a material, usually used for potting plants or sowing seeds, which can be made from single constituents or more usually a mixture of constituents such as peat, perlite, compost or loam.

In-vessel composting – A diverse group of composting methods in which the materials are contained in a building, reactor or vessel. Loam – Soil containing a desirable mixture of sand, silt and clay, suitable for crop production. Major nutrient – Essential element required in large quantities from soils by plants. Maturation – a period (within the composting process) of lower biodegradation than in the preceding steps of composting. The stabilisation continues but the rate of decomposition has slowed to the point that turning or forced aeration is no longer necessary. Some microbial activity and chemical changes, such as the oxidation of ammonium ions to nitrate, will continue. Beneficial soil micro-organisms that were inhibited or destroyed during the active composting process will begin to re-colonize the composted materials. Mature compost – compost in which biological activity (as measured by microbial respiration) has slowed. All of the easily degradable molecules have been broken down, leaving the complex organic material behind. It is difficult or impossible to identify the original feedstock materials. Mature composts usually have a dark colour and a rich, earthy smell. Micro-organism – An organism too small to see with the naked eye that is capable of living on its own. Moisture content – Percentage of a substance composed of water. Moisture content equals the mass of the water portion divided by the total mass. PAS100:2010 - See BSI PAS100:2010. Pathogen – Any organism capable of producing disease through infection. pH – A measure of the concentration of hydrogen ions in solution. pH below 7 = acidic, pH above 7 = alkaline. Potentially toxic elements – Chemical elements that have the potential to cause harm to humans, animals and/or plants. Sanitisation – Biological processes that together with conditions in the composting mass give rise to a compost in which levels of any human, animal or plant pathogens which may have been present are reduced to acceptably low levels. Secondary nutrient – Essential element for plant growth which is required in smaller quantities than major nutrients, but larger quantities than trace elements.


Sewage sludge - A semi-liquid waste with a solid concentration in excess of 2500 parts per million, obtained from the purification of municipal sewage. Also known as sludge or biosolids. Stabilisation – Biological processes that together with conditions in the composting mass give rise to compost that is nominally stable (that is a condition whereby biological activity and biodegradation has slowed and will not resurge under altered conditions such as manipulation of moisture or oxygen levels, or through the addition of a source of water soluble nitrogen). Trace element – Essential element for plant growth which is required in very small quantities. Turning – An operation that mixes and agitates material in a windrow, pile or vessel. Weed propagule – A piece of plant material from which weeds can grow (e.g. seed, rhizome or root fragment). Windrow – Elongated pile of composting material.

Acknowledgements

Thanks are due to the many individuals, companies and organisations which helped with this project.


1.0 Introduction 1.1 Project background Composts are stable, sanitised, soil-like materials, which have been made through mixing/shredding, self-generated heating and aeration. This work concerns quality composts that are PAS100-compliant, which have been made by compost producers accredited through the UK compost quality certification scheme. This project mainly concerns composts made solely from source-segregated green or garden wastes, although in some cases the composts discussed have been made from a mixture of green wastes and source-segregated food or food processing wastes. In the UK, the term “compost” is also applied to practically any substance that can be used to grow plants in. These substances (which are termed “growing media” in many other countries) often do not contain any true composts at all. Products sold as “John Innes composts” for example, are mixed using sterilised garden loam (soil) stripped from stacked turf, along with peat, sand and/or grit and added plant nutrients. In this report, the terms “compost” and “growing media”/”growing medium” are not interchangeable. Compost is defined only as in the first paragraph (above) and a growing medium is defined only as a substance or mixture of substances in which plants can be grown. Since the 1970s plants grown in pots by amateur gardeners or for retail sale have largely been grown in peat-based growing media, but this is changing due to pressure on growing media manufacturers, gardeners and professional growers to use more sustainable growing media. It is widely acknowledged that the UK horticultural industry is over-reliant on peat https://www.gov.uk/government/policies/making-the-food-and-farming-industry-more-competitive-while-protecting-the-environment/supporting-pages/horticultural-peat. It is also widely accepted that the transition to more sustainable growing media and away from an over-reliance on just one material, peat – which is also a finite and controversial material – makes good business sense for all sectors of the horticultural industry and will improve the long term sustainability of the sector, as well as having environmental benefits.

The Natural Environment White Paper (http://www.defra.gov.uk/environment/natural/whitepaper/), published in June 2011, included an ambition to reduce horticultural peat use to zero in England by 2030, setting the following milestones: a progressive 2015 target for new contracts in the public sector, a 2020 voluntary target for amateur gardeners and a 2030 voluntary target for commercial growers. It also included a commitment to establishing a “Task Force” to advise on how best to overcome the barriers to reducing peat use. The Sustainable Growing Media Task Force (SGMTF) was established in 2011, under the chairmanship of Dr Alan Knight OBE following the commitment made under the National Environment White Paper. It was made up of representatives from 35 organisations from across the growing media supply chain, including retailers, growing media manufacturers, growers and environmental organisations. The Task Force initially aimed to explore how to overcome barriers to further reduce peat use in horticulture. It has since adjusted its remit to that of putting the horticultural sector on a long-term sustainable footing by ensuring that all choices of growing media (or substrate) used for amateur gardening and horticulture are sustainable. It published several meeting notes and an interim report during 2012, and a final report to Defra Ministers in July 2012, including a draft roadmap (SGMTF, 2012). Project P6c, which was conducted as part of the work of the taskforce, was led by WRAP. It aimed to improve confidence in the use of green compost in growing media. The final report of the SGMTF (which included the report for Project P6c) acknowledged that green compost will never be the sole solution to peat replacement. However, it did conclude

https://www.gov.uk/government/policies/making-the-food-and-farming-industry-more-competitive-while-protecting-the-environment/supporting-pages/horticultural-peat

https://www.gov.uk/government/policies/making-the-food-and-farming-industry-more-competitive-while-protecting-the-environment/supporting-pages/horticultural-peat

http://www.defra.gov.uk/environment/natural/whitepaper/


that it has an important role to play in sustainable growing media manufacture and that work is required in order to improve confidence in compost, if it is to be used to a greater extent in growing media. The SGMTF suggested that the key to improving confidence lay in understanding and tackling perceived quality issues. Where it is clear that issues have been resolved, the relevant research must be signposted to industry stakeholders. The SGMTF also proposed that work should be conducted to tackle the remaining issues in relation to compost quality. In the final report and in previously published and unpublished reports, the SGMTF raised the following (real or perceived) issues as being of greatest concern:

physical contamination;

high bulk density;

high pH;

high electrical conductivity;

weed seeds;

sciarid flies and other pests;

compost shelf life;

compost variability;

presence of herbicide residues; and

the presence of human pathogens in growing media constituents (including composts)

has also been raised recently in several places (e.g. national newspapers and in industry

guidance, AfOR, 2010).

Defra published its response to the SGMTF report in January 2013, broadly endorsing it and announcing the formation of its successor, the Growing Media Panel, which will oversee delivery of the roadmap set out by the SGMTF (https://www.gov.uk/government/publications/government-response-to-the-sustainable-growing-media-task-force). At the same time, Defra announced over £600k of new Government funding to address the remaining issues with growing media and peat alternatives and, in partnership with other funders, a total package worth over £1.1m. Many companies within the UK horticultural industry are committed to peat reduction and significant progress has been made towards Defra’s targets. The Growing Media Association (GMA), which represents the majority of UK and some Irish growing media suppliers for the UK market, published its commitment to peat reduction in 2010 (GMA/HTA, 2010) and its members continue to work towards reducing their use of peat. In 2012, WRAP conducted a project which aimed to help UK growing media retailers identify peat in their supply chains and take steps to reduce the percentage of peat through the initiation of action plans. Eight leading UK retailers participated in this programme. They collectively accounted for approximately 37% of UK peat in bagged growing media and are now either instigating or strengthening peat reduction in their business through a variety of strategic and operational initiatives. All retailers identified the need to reduce the use of peat as a non-renewable, primary resource. The project also provided training on peat alternatives (including green compost) for 200 garden centre staff. The Growing Media Initiative is a further industry scheme which was developed by the Horticultural Trades Association in conjunction with the Growing Media Association, DIY and garden centre retailers, Defra, the RSPB and the Royal Horticultural Society. It was formed in an attempt to help the UK horticultural industry meet government targets for the reduction of peat use. It aims to increase awareness on the need to protect the world's peatlands and the need therefore to use more sustainable materials for growing plants and improving garden soil. Provisional GMI membership is open to retailers and manufacturers of growing media and soil improvers who are committed to achieving 90% peat replacement in their business and which are currently operating at a minimum of 20% replacement in retail

https://www.gov.uk/government/publications/government-response-to-the-sustainable-growing-media-task-force

https://www.gov.uk/government/publications/government-response-to-the-sustainable-growing-media-task-force


products. They must produce an annual Action Plan and demonstrate year on year progress. The GMI is being re-developed to encompass the sustainability criteria and a growing media performance standard that is being developed as an output of the SGMTF. At present, the majority of reduced peat and peat-free growing media is sold into the retail sector; that is, to amateur gardeners as bagged products (AHDB: HDC, 2013; Table 1). Very few UK professional growers are using peat-free growing media to grow edible or ornamental crops. The latest data show that the quantity of green compost used in both amateur and professional growing media was lower in 2012 than in 2011 (Table 1).

Table 1 Volume (million m3) of ingredients used in the UK retail (amateur) and professional growing media markets in 2011 and 2012 (AHDB, 2013). Retail media Professional media

Material 2011 2012 2011 2012

Peat 1.83 1.39 0.93 0.83

Green compost 0.43 0.35 0.02 0.01

Bark 0.43 0.44 0.05 0.06

Wood-based 0.49 0.50 0.04 0.06

Coir 0.13 0.13 0.18 0.19

Loam 0.14 0.12 - -

Most of the green compost used in growing media is used in amateur gardening products (Table 2). For example in 2013, green compost made up 10% of all amateur growing media (making it the most used alternative in this sector) but only 2% of professional growing media.

Table 2 Raw materials used (as a % of total materials used) in the amateur gardening and professional growing media markets in 2012 (AHDB, 2013) Material Growing media for

amateur gardening

Growing media for

professional use

Peat 51.8 69.1

Green compost 12.9 1.1

Bark 8.4 5.4

Wood-based 17.8 5.2

Coir 4.8 15.9

Despite the fact that there are now some very successful products on the market, some users of compost-included growing media have never gained confidence in its use and some growing media manufacturers have had their confidence dented through past use of poor quality compost that was unsuitable for inclusion in growing media. Poor uptake of composts has been attributed by various industry experts as being due to several reasons, of which poor compost/growing media quality and consistency are only two. Other reasons include confusion over what the terms ‘compost’ and ‘growing media’ actually mean (which can be further complicated by poor labelling of products), lack of specialist technical information on how to use the product(s) to best effect, cost, poor availability of appropriate products in some geographical areas and a lack of willingness to change. The fact that peat is becoming more difficult (and probably more costly) to obtain and the fact that it is increasingly being labelled as a finite resource which should be replaced by more sustainable products, is likely to result in increased interest in PAS100 composts for use in growing media. For that reason, it is important to ensure that sufficient composts of


suitable quality are available, along with appropriate development work where required and technical advice to help develop these relatively new markets. In an effort to help increase the production and use of PAS100 composts of suitable quality for use in growing media, WRAP has previously published guidance (WRAP 2011a and b). These important publications will be further discussed later in this report.

1.2 Benefits of using composts in growing media Anecdotal evidence from growers and growing media specialists, along with published results from previously undertaken growing trials using compost-included growing media, have shown that such media can have several advantages over peat-based media when managed appropriately. For example:

Compost provides major and secondary plant nutrients and trace elements. There is the

potential for growers or growing media manufacturers to save on fertiliser costs. Compost

can provide nutrient holding capacity in the growing medium in a similar way to loam;

Compost has a neutralising value and it will almost never be necessary to add lime to

growing media which include composts, thus providing a further opportunity to save

costs;

Compost may assist in the suppression of some plant diseases because it is more

biologically active than other growing media constituents. It is thought that the natural

populations of micro-organisms in compost can out-compete, or in some cases directly

attack, plant disease-causing organisms;

Compost may reduce the surface growth of liverworts, moss and algae when used in

growing medium blends that tend to retain a drier surface than media based solely on

peat;

Compost-included growing media tend not to require a synthetic wetting agent as peat-

based products do in some applications;

Compost-included growing media tend to slump less over time than peat-based growing

media;

There is potential to use less water when managing plants grown in compost-included

growing media than in peat-based media if irrigation is appropriately managed;

Some nurseries have found that it can be faster to pot with compost-included growing

media than with peat-based media. This was found to apply to both hand and machine

potting; and

Growing media which are based partly on composts generally have a higher bulk density

than those based on peat. This is considered a disadvantage in some applications (e.g.

where there is a requirement for a lot of manual handling of products or a need for

lengthy transport of media or plants). However, it is an advantage in others (e.g. where

relatively unstable top-heavy potted plants, such as some conifer or climber species, are

situated in a windy site – a heavier pot helps to stop the plants blowing over).

Even though the benefits of including composts in growing media have been well documented, previous WRAP studies and the experiences of individuals within this project team have shown that there are continuing concerns about compost quality amongst growing media manufacturers, growers and retailers and these concerns have been reflected in the conclusions of the SGMTF (as outlined above). Several respondents to our survey said that they would like to see more scientific proof of some of the benefits of using composts in growing media.


1.3 Project rationale and aims For over 10 years, WRAP has been committed to improving the quality and availability of PAS100 composts. It is committed to developing markets for composts and this includes increasing the use of composts in growing media and increasing the use of compost-included growing media in both amateur and professional horticulture. Between 2005 and 2008, WRAP funded several nursery-based trials of compost-included growing media. In 2011, WRAP developed guidance intended to help promote and facilitate the use of quality composts in growing media (WRAP 2011a and b). WRAP has also taken an active part in the work of the SGMTF (SGMTF, 2012). One of the goals within the Roadmap is to ‘improve confidence in the use of green compost such that it is able to fulfil its maximum potential in the growing media market’ (currently estimated to be around 20% of the market [SGMTF, 2012]). This project addresses one of the tasks set out under that goal within the roadmap. It aimed to ascertain whether each issue identified by the Task Force (other than that of herbicide contamination) is current or has already been resolved. If an issue has been resolved, the means by which it was resolved has been documented and published in the report. If an issue remains, the nature of the problem has been discussed and the means by which it might be addressed outlined. This work is important in order to improve understanding of how to manufacture composts of appropriate quality for use in growing media and in order to increase the use of quality composts in growing media. The project tasks are set out below. A. To interview a selection of PAS100 compost producers, professional growers, growing

media manufacturers and other relevant stakeholders in order to obtain their views and information on their experiences in making, supplying and using composts.

B. To conduct a desk-based investigation of previous trials work and research on specific aspects relating to the quality and use of green composts in growing media and to produce a short report with bibliography to provide easy access to relevant information. Aspects studied included:

physical contamination;

high bulk density;

high pH;

high electrical conductivity;

weed seeds;

sciarid flies and other pests;

compost shelf life;

compost variability; and

the presence of human pathogens.

C. To produce a hyperlinked summary of UK legislation and good practice guidance relevant to the safety and quality issues associated with using composts in growing media.

D. To complete a gap analysis to determine where additional basic research is required in order to increase the use of composts in growing media.

E. To propose mechanisms for knowledge exchange (KE) whereby practical industry experience can be shared without compromising the commercial integrity of individual businesses.


2.0 Methodology A range of issues are known - these were checked with industry stakeholders, and desk-based investigation undertaken to determine whether they had actually been addressed. Where they had been addressed, signposts to relevant research were gathered and are listed in Section 3.2. Where they have not been addressed (or only partly addressed), the gaps have been collated and presented in Section 3.4.

2.1 Interviews of industry stakeholders Industry stakeholders hold important information and opinions on the value of composts in growing media, the challenges of using them and ways to address these challenges. For that reason, a range of key stakeholders were interviewed as part of this project. A list of twenty eight interviewees was compiled including eight compost producers of whom seven also produced growing media, an additional four growing media manufacturers, ten growers and six retailers. Three different questionnaires were produced - one for composters and/or growing media manufacturers, one for growers of horticultural crops and one for retailers of growing media (Appendix 2). Each contact was phoned in advance, introduced to the project, asked if they would be happy to participate and whether they would prefer to complete the questionnaire electronically (for submission by email) or over the phone. Of those asked to participate in the project, seven of the compost producers agreed (six of which were also growing media producers) and three of the four additional growing media manufacturers agreed. Eight of the growers and two of the retailers participated in the project. Once the interviews were completed, the results were reviewed and summarised in an overview, a series of simple tables, graphs where appropriate and summary statements (Appendix 1). Most of those who responded wished to remain anonymous and so no names of individuals or companies are mentioned in this report. 2.2 Desk-based investigation The nine key topics for investigation in relation to the use of composts in growing media were: 1 physical contamination; 2 high bulk density; 3 high pH; 4 high electrical conductivity; 5 weed seeds; 6 sciarid flies and other pests; 7 compost shelf life; 8 compost variability; and 9 human pathogens. The project team compiled a list of publications relevant to each of the nine topics. They then used the references sections within them (where relevant), discussions with stakeholders, and web-based literature searches to ensure that all additional key relevant documents were identified. The search engines Google Scholar and CAB Abstracts (which includes a range of horticultural journals and conference proceedings) were used. These search engines and Google were also used to obtain final and progress reports from relevant desk-based studies and experimental projects. It quickly became obvious (as anticipated) that UK research and development reports were generally most relevant to the project, although international journals were included in the literature searches. UK journals and publications were more relevant because UK composts tend to be different from those made in Europe and the USA in terms of feedstock and product quality. For example, much of the


compost made in other countries contains sewage sludge and/or is based on non-source-segregated wastes. Literature relevant to each of the key topics of investigation was read and assessed, and a draft report for each topic was prepared, which discussed:

the background to the issue and reason(s) why it is important; and

the extent to which the issue has been partly or wholly addressed in the industry.

Each of the nine draft reports included full references to all relevant work (with web links for on-line readers where possible) including research, development and (where possible) details of methods by which individual compost producers or growers have addressed the issue (information obtained during stakeholder interviews). The draft reports, prepared by individual authors were then reviewed by the other project team members, sent to the WRAP project management team for their comments and updated prior to submission of the final version of the report (Section 3.1). 2.3 Hyperlinked summary of UK legislation and good practice guidance Several pieces of UK legislation and good practice guidance have been developed with the aim of protecting people, animals, crops and the environment from the risks and challenges associated with compost production and use. Guidance also exists to help compost producers make their products as useful as possible in the context of growing media markets. In this part of the project, a brief description was made of the main pieces of legislation and good practice guidance which aim to reduce the impact of the main issues (risks and challenges) associated with the use of composts in growing media (Section 3.3). Hyperlinks are given to the relevant legislation and good practice guidance. This part of the report can be read on paper but an internet connection is required for full functionality. 2.4 Gap analysis to determine where additional research is required Gap analysis was conducted to determine where information was lacking with respect to knowledge of techniques to minimise problems relating to the nine issues being investigated in this project. Gaps in knowledge were first identified during a “brainstorming session” by the project team members following completion of the main stakeholder interviews in Task A, along with Tasks B and C and circulation of draft reports associated with these tasks. Notes were taken during the brainstorming session and a draft gap analysis was completed and circulated to the team members for comment. This report contained the following information for each identified issue:

signposts to recent relevant research/trials work;

conclusions on whether the research report/results were visible enough

if so, are they being sufficiently used/put into practice?

if not, is more work required?

are individuals/organisations solving the issue themselves and if so, can they assist in

moving things forward (what barriers are being put in place due to commercial

sensitivities?);

current practice to minimise risk and/or maximise product quality;

has the issue been resolved or is it still an issue and if so, with which group(s) in

particular; and

work required to resolve the issue.


A limited amount of further literature searching and telephone calls to stakeholders was conducted in some cases in order to complete the final version of the Task D report. 2.5 Proposal of knowledge exchange (KE) mechanisms The project team assessed the information gained through completion of Tasks A to D, considered the options based on their experience in education, training and knowledge exchange (KE) and suggested a range of KE mechanisms for use in this challenging sector. These are outlined in Section 3.5. 3.0 Results and discussion 3.1 Interviews of selected industry stakeholders As part of the project we aimed to gather information through a survey of key players in the composting, growing media manufacturing, retailing and growing sectors. The full results of the interviews are presented in Appendix 1 and the questionnaires used as the basis of these discussions are given in Appendix 2. Of those invited, seven compost producers (of whom six also produced growing media) took part in the project, along with an additional three growing media manufacturers, eight growers and two retailers. Despite the fact that not all invited stakeholders took part, it was felt that the responses fairly represented the views of the major industry players. 3.1.1 Summary of stakeholder views The opinions of the 28 stakeholders interviewed as part of this project differed markedly from one to another in some cases, with some holding largely positive views about compost quality and the use of PAS100 composts in growing media, and others largely negative views. While all of the compost producers and growing media manufacturers were aware of the WRAP specification and guidelines (WRAP 2011a and b) the majority of the growers were not. The full results of the interviews are presented in Appendix 1 of this report. In summary:

The views of the seven compost producers (of whom six also produced growing media)

and additional three growing media manufacturers differed greatly. Some have worked

very hard to meet the needs of the CIGM market and felt that most of the nine issues had

been effectively solved, whereas others felt that none of them had. Most had some

remaining concerns, and most often, those included the presence of physical

contaminants, high compost bulk density and high compost EC;

Of the eight growers interviewed, two used CIGM to some extent, two did not know

whether their growing media contained composts, and the remaining four did not

currently use CIGM. For the growers, physical contamination and lack of consistency in

the product were the major barriers to use of growing media containing PAS100 compost.

Five out of eight growers listed physical contamination as a major barrier, and six out of

eight cited lack of consistency. However, nearly all of the factors listed were deemed a

barrier to use for one or more of the growers interviewed. The growers who had negative

perceptions of compost had either not tried CIGM themselves or had tried poor quality

media some time ago;

Of the two growing media retailers who took part in the project, one sold growing media

based partly on composts and one did not, due to concerns over all nine of the issues

under study in this project. The retailer who did sell CIGM felt that physical

contamination, high bulk density, sciarid flies, shelf life/consistency of product, and poor

customer perception limited sales; and

It is important to state that many of the negative views which stakeholders held about

composts and CIGM were based on previous bad experiences (or the experiences which


colleagues or associates had) with unsuitable PAS100 composts, non-PAS100 composts or

CIGM based on them, rather than with composts made recently according to the WRAP

Specification and Guidelines (WRAP 2011a and b) or CIGM based on these improved

materials.

3.2 Desk-based investigation Based on the feedback received from the industry stakeholders, a programme of desk-based investigation was undertaken to determine whether the nine principle areas of concern had already been addressed. The extent to which the main conclusions from these pieces of work are understood by industry stakeholders is discussed for each topic along with the extent to which each issue has been resolved. Recommendations are then made for minimising the impact of the issue in future. 3.2.1 Physical contamination Introduction Contamination of composts with glass, plastic, metal and stones remains a concern for practically all growing media manufacturers, retailers and growers. Sharps (pieces of glass and sharp metal fragments) are a particular concern due to their potential for causing injury to those handling compost or growing media. Stones are less of a problem if the amount present falls within the PAS100 limits, but visible plastic contamination is unpopular with all users of compost and CIGM. Many compost producers (including those interviewed in this project) complain about the amount of physical contaminants within the feedstocks which they are expected to compost. Several of the growing media manufacturers contacted in this project complained that green composts typically contain too many physical contaminants. Some retailers and most of the growers interviewed also complained about the amount of physical contaminants typically present in CIGM, and writers in the gardening press often complain about physical contaminants present in bags of reduced peat and peat-free growing media (e.g. Colborn, 2011). Whether these complaints were due entirely due to recent experience, to historical experience or even to perceptions based on the bad experiences of others was sometimes difficult to discern. Previous and current relevant work Researchers worldwide have cited the presence of physical contaminants in composts and have outlined or discussed the problems which these contaminants can pose when seeking appropriate markets for contaminated composts (e.g. Brinton, 2000; Dimambro et al., 2007; Ostos et al., 2008). Most of the composts considered as potential constituents of growing media in the USA or in mainland European research were based on non-source segregated wastes, and for that reason were likely to contain much higher quantities of physical contaminants than those principally under discussion in this report (i.e. composts accredited under the UK compost quality standard, BSI PAS100). Given that the long term aim of this project is to help improve the quality of UK PAS100 composts, this review will consider mainly composts made from source segregated feedstocks which do not include sewage sludge. No scientific publications (other than one by WRAP [2002] and that by Dimambro et al., 2007) have reported the percentage of physical contaminants found in UK composts since BSI PAS100 was first published in 2002. In the former report (which is the only one to have tested a relatively large number of samples), monthly samples were taken from each of nine compost sites which were either PAS100 accredited or had been working towards accreditation for a period of 5 months. The quantities of glass, plastic and metal contaminants found in composts were extremely low (generally below 0.1%).


No published studies have dealt with the impact of feedstock collection and composting methods on contamination levels in finished compost. This is probably because many of the methods which could (and should) be employed to minimise contamination in the finished product are rather obvious and research is not thought to be necessary. If the feedstock going into the composting process is free from contamination, then it is logical that the finished product will also be free from contamination. However, it can be very difficult to ensure that feedstock is clean, particularly when the composter does not have full control over the collection process. In reality, a combination of measures aimed at reducing physical contamination in the finished compost are used in practice on composting sites, including steps taken to reduce the presence of physical contaminants:

in incoming feedstocks;

in feedstocks on site, prior to shredding;

in compost during the composting process; and

in the finished product(s).

ORG and REAL (which owns the only UK compost quality certification scheme, BSI PAS100) has been aware of the problem of physical contamination of composts for many years and has prepared several templates which provide guidance to help compost producers to consistently achieve at least the standards required under PAS100:2011. These are available to new applicants and members on the scheme. The current (PAS100:2011) standards for maximum levels of glass, plastic, metal and stones represent a tightening of the rules (from those last published in PAS100:2005) in response to industry pressure for better quality composts, and the ability of compost producers to meet these quality requirements. The standards are shown in Table 3.

Table 3 BSI PAS100:2011 standard for physical contaminants. Parameter Test method Unit Upper limit

Total glass, metal, plastic and any

other non-stone fragments > 2

mm

AfOR MT PC & S* % mass/mass of

“air dry” sample

0.25 of which

0.12 is plastic

Stones > 4 mm in grades other

than “mulch”

“ “ 8

Stones > 4 mm in “mulch” grade “ “ 10

*This method instructs laboratories to determine and report sharps as part of the reporting on

each type of physical contaminant (glass, metal, plastic, stones and other non-stone fragments)

The Organics Recycling Group recognise that the quantity of physical contaminants in composts remains a problem for some compost producers and users, and has formed a special interest group on feedstock quality and contamination in order to develop long-term solutions. They (under their previous name, AfOR) have published a series of template documents aimed at helping composters tackle feedstock contamination with a view to reducing the amount of physical contaminants in finished composts. For example, they have recently updated their template for the standard operating procedure of composting sites, which includes sections on “Contracts/agreements/communication with waste suppliers”, “Rejection or acceptance and storage of input materials” and “Traceability of input materials”. All of these sections aim to help composters design procedures which will minimise the presence of physical contaminants in feedstock and therefore in the finished product. In March 2012, ORG (then AfOR) released two input specification schedule templates that enable composters and their suppliers to define a standard for the quality and types of input materials delivered to their composting sites. Versions are available for green waste and for co-mingled food and green waste composting systems. The templates can be adapted to


include any other biodegradable wastes that are allowed under contractual arrangements between the composters and their waste suppliers. This input specification template also provides guidance on how the input materials delivered to the composting facility should be compared to the input quality standard and defines the actions to be taken if it is established that the material does not meet the required standard. Use of the templates is not mandatory under the UK Compost Certification Scheme but ORG recommends that this, or an equivalent template, is used by the composters and their suppliers when signing up new contracts or reviewing existing contracts. BSI PAS100:2011 was developed as a baseline standard. Compliance with PAS100 was never intended to mean that composts were suitable for all markets. The minimum quality values stated within PAS100 are simply not high enough for some markets, including growing media manufacture, although the standard does stipulate that composts must be fit for purpose for the markets for which they are intended.

In recognition of this, WRAP developed additional specification guidance for specialist end-uses of composted green materials in 2004 (WRAP, 2004a). The guidelines aim to assist producers of composted green materials to better understand and meet the specific requirements of growing media manufacturers and growers who mix their own growing media. The guidelines also help provide these customers with a framework for the establishment of appropriate purchasing specifications as part of supply contracts. They were developed in partnership with the Growing Media Association, with input from ORG (then the Composting Association) and other experts. The guidelines were thoroughly revised and re-published in 2011 following extensive consultation with industry experts and other stakeholders and were published in two parts. To help composters use the ‘Guidelines for the specification of Quality Compost in growing media’ (WRAP, 2011a, Section 3.3.4), WRAP also produced the ‘Good Practice Guide’ (WRAP, 2011b, Section 3.3.5). Amongst other things, the guide aims to inform compost producers about opportunities in the growing media sector. It also aims to help compost producers understand the need for measurement of specific quality parameters in green and green/food derived composts intended for use as constituents of growing media and helps them achieve the more stringent requirements in terms of compost quality. It also aims to help growing media manufacturers understand more about composts, how to specify them and how to use them as constituents of growing media. These two documents have great potential to help improve the quality and consistency of compost products in terms of their use as growing media constituents, and there is some evidence (from the survey conducted in this project) that both compost producers and growing media manufacturers are aware of them and are using them to good effect. Compost made according to the Good Practice Guide aims to solve the majority of the issues under study in this report. The guidelines recommend that compost producers should aim to eliminate all physical contaminants from their composts, and that growing media manufacturers set lower limits for the permitted quantities of physical contaminants in composts than those in PAS100:2011 (Table 4). The good practice guide provides advice on how compost producers might achieve these more stringent specifications. Two of the leading experts in growing media manufacture (who wished to remain anonymous) felt strongly that some of the problems with physical contaminants in composts and growing media in the industry today were perceived, rather than real. They felt that many growing media manufacturers, CIGM retailers and growers had had bad experiences with poor quality composts/CIGM in the past and had decided, based on these experiences that these products were not for them. Those who decided against composts have since been unaware (and in many cases, unwilling to be made aware) of the significant


improvements which have recently been made in the quality and potential performance of composts and CIGM. In some cases, these individuals continue to speak out against composts and CIGM at public meetings and in the press, which may be limiting market development. The compost producers who have succeeded in largely solving the physical contaminants problem have spent considerable amounts of time and money on it. In particular, they:

have worked with their suppliers in order to reduce the volumes of physical contaminants

coming in with the feedstock;

have set up manual picking lines (and similar) to remove physical contaminants prior to

shredding;

have purchased sheds and fences to minimise air-blown contamination of windrows (from

plastics) during composting; and

employ manual labour to remove contaminants from windrows following turning and

employ a range of mechanical means (e.g. magnets, air density classifiers and screens) to

remove physical contaminants toward the end of the composting process.

These compost producers admit that it costs much more money to make “clean” compost than compost which contains unacceptable quantities of physical contaminants. However, this extra cost can be balanced by extra revenue from the more demanding markets, such as growing media.

Table 4 Recommended targets and limits for the main quality parameters of composted material that is to be used as a growing medium constituent. (Values obtained from WRAP, 2011a). Parameter Test

method Unit Target Upper limit Comments

Sharps AfOR MT

PC & S*

Present

or absent

Absent Zero Physical contaminants that

are sharp are unacceptable in any application where

compost is handled and/or

used in growing media.

Stones “ % w/w

dry matter

retained on lab

sieves

Absent 2% stones of >

4 mm, no stones

> 8 mm

None > 4 mm shall be

found on visual inspection

at delivery.

Metal, glass

and plastic

> 2 mm*

“ “ Absent 0.2% metal

0.05% plastic

0.1% glass

None > 2 mm shall be

found on visual inspection

at delivery and a single presence suggests non-

compliance.**See note below for overall PAS100

total limit for glass, metal

and plastic and any “other” non-stone fragments.

*This method instructs laboratories to determine and report sharps as part of the reporting on each type of physical contaminant (glass, metal, plastic, stones and other non-stone fragments)

**Despite the individual limits above, the overall limit in PAS100:2011 that must be adhered to for

“Total glass, metal, plastic and any “other” non-stone fragments > 2 mm is 0.25%. PAS100 also requires the total level of plastic > 2 mm to be no more than 0.12%. However, this guide

recommends that plastic > 2 mm should be no more than 0.05%.


Recommendations for minimising the impact of the issue in future The best way to continue to reduce the concentration of physical contaminants in composts is to ensure that all of those involved in the sector are aware of all relevant best practice guidance, which details the necessary steps for them to take. There are existing, well-documented solutions to the problem of physical contamination in composts and some of the leading compost producers and growing media manufacturers interviewed as part of this project have said that these solutions, when implemented in full, can be sufficiently effective, though they take time to implement to the full and do cost money. Of those consulted as part of this project, all compost producers and growing media manufacturers were aware of the two recent WRAP publications (WRAP, 2011a and b). However, those consulted represent the industry leaders, many of whom were involved in the stakeholder consultation process undertaken during production of the publications. In short, they would be expected to know about the publications and would be more likely to put the recommendations within them into practice. On the other hand, members of the project team working with smaller or newer composters wishing to start supplying composts into the growing media or other high value sectors have found that managers on these sites are frequently not aware of recent improvements to the AfOR PAS100 templates (these have very recently been re-branded as the Renewable Energy Assurance Ltd. (REAL) templates) or the relevant WRAP publications (2011a and b). For this reason, promotion of the revised and updated REAL templates within and relating to PAS100:2011 and the WRAP publications (2011 a and b) through articles in the trade press, targeted emails to members of the PAS100 scheme and cost-effective training courses are recommended as the most effective way of continuing to reduce physical contaminant levels in composts. It is important to note that the margins for cost-effective production of quality composts from green and food wastes are tight. Not all compost producers can be convinced of the need to invest in their production systems if the prices that they are achieving for their compost products remain uneconomic due to poor feedstock quality or distance from markets.

3.2.2 High bulk density Introduction A major constraint to the use of compost at high inclusion rates in growing media is that it has inherently higher bulk density than most other ingredients, with the exception of sterilised loam, when used in growing media. The reason for the high bulk density is that compost typically contains around 25% mineral material associated with 75% organic matter, the mineral fraction being much denser (Schmilewski, 2008). WRAP guidelines (WRAP 2011b) propose that the maximum bulk density of compost for inclusion in growing media should be no higher than 550 g/l and preferably within the range of 400-500 g/l. High bulk density will increase the cost of transport of growing media and may also increase handling costs at the nursery. Consideration needs to be given to the maximum size of bags containing compost for both professional and retail customers as well, as bags must not be too heavy to lift. In the questionnaires one major retailer saw customers having to handle heavy bags as a major problem. There are however advantages to growing media with higher bulk density, for example container nursery stock pots are less likely to blow over in exposed windy sites, and Rainbow (2009) has reported that less firming in of liners was required when potting in peat-free growing media containing around 33% green compost compared to standard peat-based mixes. Previous and current relevant work Inclusion of high volumes (by percentage) of compost in growing media may also impede drainage of crops, the main reason being that the mineral material in compost, having a low particle size will fill in the gaps between particles within the mix and thereby reduce the


volume of pore space. These gaps can contain either air or easily available water depending on the saturation of the growing medium. Prasad et al. (2001) looked at increasing the ratio of green compost to peat from 20 to 50% inclusion by volume, and measuring bulk density and easily available water content. Increased compost inclusion rates increased the bulk density of the mixes and reduced the pore space of the growing medium. Inclusion of up to 20% green compost produced only small effects on easily available water content (that is water which can be easily taken up by growing plants without reaching wilting point), but when increased to 50% green compost, the easily available water content dropped significantly (from 25% to 19% easily available water with the reduction of pore spaces). This is very important when considering crops which stand outside for long periods e.g. container nursery stock. Blending materials which are lightweight and very free draining will provide a solution to the problem of excess water retention. Schmilewski (2008) postulated that to keep the same air capacity (25%, which would be the target for containerised nursery stock), this could be achieved either using 0 – 20 mm peat grades alone or a peat-free blend of 40% green material, 30% composted bark and 30% wood fibre. The air capacity was identical for both growing media, but the wet bulk density was doubled for the peat-free mix due to the presence of the compost. Variability of bulk density between green compost samples is mentioned by many authors (for example Surrage and Carlile (2008) who sampled 15 sites in Nottinghamshire and found that bulk density of composts (only some of which were PAS100 accredited) varied fourfold between 243 and 837 g/l). In work conducted on behalf of WRAP, composts from nine sites were sampled over a period of 12 months and it was found that the mean bulk density varied little during the year, with typical average bulk density values ranging from 480 to 620 g/l (WRAP, 2005). These composts were all from PAS100-accredited sites or sites who were working towards PAS100. Bulk density was consistently higher for some composts than others, with two of the nine products tested averaging 675 and 629 g/l over the year (respectively) and a further two products averaging 442 and 444 g/l respectively. There has been no work conducted to determine the range of bulk density values obtained from composts produced according to the WRAP Specification (WRAP, 2011a). The resultant problem of high weight deterring manufacturers of growing media from including compost in mixes and the public’s reluctance to buy based on heavy bag weights has also been noted. To illustrate the typical bulk density of a range of products used in peat-based and peat-free growing media the data in Table 5 have been derived from a number of sources:

Table 5 Bulk densities of several potential growing media constituents and soil Product Bulk density g/l Product Bulk density g/l

Irish moss peat 200 - 300 Composted bark 380

Coir (rewetted) 250 - 350 Aged pine bark 380

Wood fibre 50 - 150 Aged conifer bark 390

Wood fibre (Germany) 160 Bark fines 360 - 420

Shredded chipboard 350 Sterilised loam 1200 - 1300

From the above table it can be seen that the addition of green compost with a typical bulk density of 450 – 550 g/l could increase the final bulk density of mixes considerably. Examples of mixes containing green compost (which has an assumed bulk density of 500 g/l for this purpose) and the effect on bulk density of peat, coir and composted bark mixes are shown in Table 6. A value of 500 g/l for the bulk density of compost was used here because


several of the surveyed composters who were also growing media manufacturers indicated that it was an achievable target value.

Table 6 Percentage composition (by volume), bulk densities and weights of a range of typical growing media mixes Product/bag

(volume)

% green

compost

% other Final BD

(g/l)

Wt pack mix

(kg)

Wt. Pack (kg)

100% peat

Retail MP (60 l) 25 75 (peat) 313 18.8 15

Retail MP (60 l) 25 75 (coir) 350 21.0 15 Retail MP (60 l) 25 75 (comp. bark) 410 24.6 15 Growbag (30 l) 50 50 (comp. bark) 440 13.2 7.5

MP – multipurpose retail growing medium, 60 litres is a typical pack size Growbag – 30 litres is typical volume for a number of manufacturers of retail growing media

A 60 litre retail multipurpose growing medium (using for example 25% green compost and 75% bark) has a weight of almost 25 kg, which is the maximum weight of, for example, bags of fertiliser used in the horticulture industry. There is no maximum weight for lifting defined by HSE, but an average retail customer might well have difficulty lifting a 60 litre peat-free mix with the above formulations; a lower volume would need to be used for a peat-free mix or the amount of green compost in the mix reduced. In the second example, 50% green compost could be used in growbags for retail salad crop production in a peat-free mix. Compared to the equivalent volume of a 100% peat product it is double the weight and would cost a lot more to transport, with fewer bags per pallet. Traditional loam-based products such as the John Innes range, which must contain a mix of sterilised loam, sand and/or grit and peat, have considerably higher bulk density values than standard growing media. The bulk density of such mixes is quoted by the John Innes Manufacturers Association (JIMA) as typically 800-950 g/litre (JIMA, 2010), which is higher than mixes listed in Table 6. For that reason, following a study of most of the JIMA members’ 2013 catalogues, typical John Innes mixes are sold in 25 litre bags, compared to standard peat-based or peat-free mixes of typically 50-60 litres. There is a case for marketing growing media containing higher amounts of green compost. Such material would contain more mineral material and would have to be sold in smaller bags due to the higher bulk density. Product buyers would have to be made aware of why the bags are heavier and the advantages of adding the green compost (more mineral material means greater buffering capacity, better water retention etc.). Adding further amounts of sterilised loam and grit/sand will give characteristics similar to traditional JI mixes but without the peat content and such mixes are already available for retail sales. It should be emphasised that no reference can be made to John Innes on the labels of bags containing compost and no peat, since John Innes mixes must contain peat, and under current rules inclusion of green compost is not allowed. Extent to which issue has been resolved Most of the professional nurseries and at least one major retailer surveyed in this project see high bulk density as a factor which either prevents or would limit the use of compost in their growing media. However, two producers of compost who also manufacture growing media stated that with attention to feedstock management, problems with bulk density can be overcome. They did accept that high bulk density would generally limit inclusion rates due to the fact that mineral material was always going to be present, even in well managed feedstocks. Likewise, growing media manufacturers who used PAS100 composts in their mixes made the same point.


Matured compost stored under covers (rather than in the open) stays drier and several growing media manufacturers made the same point that compost needs to be covered during the maturation stage to ensure it does not get wet, which would increase bulk density. Due to the nature of compost, unless the mineral fraction can be reduced, the bulk density will always be high compared to many other potential ingredients in growing media, such as bark, wood fibre and coir. Soil and small stones may be present in householders’ green bins for example. These often form part of rootballs of dead or unwanted plants. Soil has a high bulk density (see Table 5, sterilised loam) and won’t be screened out using 0-10 mm screens at the start of the composting process (soil by definition is material below 2 mm). Educating the public as to what can go in to green bins may help here, together with vigilance at the reception point for green waste before composting. Recommendations for minimising the impact of the issue in future Keeping compost as dry as possible during the maturation stage, when higher moisture levels aren’t required for rapid biological activity will undoubtedly help, either by using buildings for maturation or covering windrows to minimise rain ingress. It is possible that green material from certain sites e.g. parks, cemeteries and landscapers is “cleaner” with less mineral matter present. If such material can be segregated and used specifically for compost destined for the growing media market, there would be more chance of a lower bulk density material. In-vessel composting allows air to be blown into the bottom of the vessel which will help to aerate the material which in turn will be lighter (comment from one compost producer in the survey). In an idealised world, educating the public to avoid putting small stones and soil in their green bins would also help. Such guidance might involve encouraging householders to shake and knock off as much soil from roots and rootballs as possible before putting dead and unwanted plants into recycling bins. However, to what extent local authorities can enforce this is open to debate. Vigilance at the reception points of green waste before composting may help if it can be seen that quantities of soil are present in a load. WRAP produces guidelines to local authorities for managing garden wastes at Civic Amenity sites (WRAP 2005d), which includes having dustbins for the public to deposit plastic bags used to transport the garden waste and trained site operators to explain what can and cannot go into the waste skips. Walsall Council has written a leaflet which says what can and cannot go into green waste bins, which can be seen on the WRAP website (Walsall Council, 2008). WRAP’s link for local authority advice on collections can be found at: http://www.wrap.org.uk/category/sector/local-authorities. The WRAP Specification and Guidelines (WRAP, 2011a and b) provide clear information as to target values for compost bulk density and on methods for achieving these values. It is important to ensure that compost producers producing, or interested in producing composts for use in growing media know about these publications and have read and understood them.

3.2.3 High pH Introduction The pH of a growing medium refers to its acidity or alkalinity and is very important as it has a major impact on nutrient availability (Bunt, 1988). Peat is naturally quite acidic (its pH is around 4.0), hence lime can be added to raise the pH to the desired level for the type of plants being grown (generally 5.5-6.0 for general species and 5.0-5.5 for acid-loving ‘ericaceous’ species). High pH in a growing medium commonly causes deficiencies of manganese and iron and also reduces the availability of phosphorus. It is very difficult in practice to lower the pH of a growing medium as addition of acid can create toxicities. For growers in areas of ‘hard’ water (high bicarbonate content), the pH of the growing medium

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will rise over time anyway, so for longer-term crops it is sometimes recommended to start with a slightly lower pH to allow for this (Holmes & Hewson, 2005). Green compost naturally has a relatively high pH compared with peat (typically 7.0 – 8.5), and when it is used as a growing medium component, even at modest percentages, it results in a higher pH than is recommended for peat-based growing media. This has caused concerns to growers and growing media manufacturers in the past, although it is generally recognised now that a peat mix with a pH of 7.0 (achieved by addition of lime) is not the same as a peat/green compost mix with a pH of 7.0 because the latter behaves more like a soil than a soil-less growing medium and has greater ‘buffering’ (that is, it holds and subsequently releases nutrients on the surfaces of organic particles). A growing medium containing green compost can therefore have a higher pH than a peat-based one and still have good availability of phosphorus and trace elements. It is not the actual pH that is important for plants, but the effect it has on nutrients and their availability to plants. There is a significant difference in the effect of pH on nutrient availability between soils and peat-based growing media (Bunt, 1988). A growing medium containing green compost is more similar chemically to a loam-based medium than a peat-based one. Less mature composts contain more ammonium N and therefore have a higher pH than mature composts, because a higher proportion of ammonium ions in solution will make the pH more alkaline. This is another reason for only using stable, mature composts in growing media.

Previous and current relevant work Many trials have demonstrated the increased pH in growing media containing green compost when compared with peat-based media (for example Maher et al., 2001). However, at typical inclusion rates (10-30%) this pH increase does not cause problems for most plant species. Most growers of ericaceous crops that require more acidic growing media have reservations about the use of green compost, but such crops also need a lower electrical conductivity so only low rates of green compost would be used anyway. The ‘Peatering Out’ trials commissioned by WRAP (STA0013) demonstrated that, despite growing media containing green compost having a higher pH than standard peat-based media, the normal problems associated with high pH (such as iron deficiency) did not occur (only non-ericaceous plants were included in the trials). Other WRAP growing trials have also demonstrated this at Ness Botanic Gardens (WRAP project ORG033-14) and at Aldingbourne Nurseries (WRAP project ORG0033-18). The WRAP guidelines for compost for growing media specify a pH of 6.0-8.0 as being acceptable (WRAP, 2011a). Most green composts have a pH of between 7.0 and 8.0, which is within the acceptable range. Composts with a very high pH are probably not mature enough to use in growing media anyway. Extent to which issue has been resolved Growing media manufacturers using compost who responded to the questionnaire commented that the pH of compost is related to stability/maturity and high pH readings are associated with immature composts. Compost pH is not a barrier to the use of composts at typical rates in a growing medium for most species. Factors other than high pH (such as high compost salt concentrations) are barriers to the use of green compost in media for ericaceous plants. Most growing media manufacturers do not consider pH in itself as a barrier to the use of compost in growing media products but half of those surveyed in this project said that the high pH of compost limited the amount they would use in a mix.


Recommendations for minimising the impact of the issue in future If mature composts are used in growing media, the issue of pH will not be a factor for most plant species at typical compost inclusion rates. The WRAP guidelines include information on compost maturity and how to measure it (WRAP, 2011a). 3.2.4 High electrical conductivity Introduction High electrical conductivity (EC) in a growing medium can be a problem, especially for young plants and salt sensitive species. High EC damages plants because when the concentration of salts in the soil solution around the roots is higher than the concentration of salts within the root cells the roots can no longer take up water effectively, causing stunting of growth and eventually plant death. High EC can be particularly damaging to the roots of young plants and salt sensitive species, for example ericaceous plants. Certain salts can also be toxic to plants at high levels (known as the ‘specific ion effect’) and this will also damage plants (Handreck & Black, 2010). Peat has a naturally low EC which means that fertilisers can be added to raise the nutrient status with minimal risk of increasing the EC too much. Green compost has naturally high concentrations of salts such as those of potassium and chloride, which results in a high ‘background’ electrical conductivity (EC) compared with peat. Composts using food waste as well as green waste as feedstocks tend to have a higher EC than those just made from green waste. When composts are blended in a mix with materials of low EC, such as peat or bark, this issue can be managed, but it is one of the reasons why optimum rates of inclusion of compost in growing media are generally below 50%. The effect of high salt levels from higher inclusion rates of compost have been demonstrated in many studies (e.g. Maher et al., 2001). Variations in EC between batches of compost are a particular problem for growing media manufacturers who need to amend fertiliser additions based on the contribution of nutrients and salts from the compost used. As with pH, growing media containing green compost have a higher chemical buffering capacity, i.e. the ability to hold and subsequently release nutrients from exchange sites on particle surfaces. EC levels that would be considered potentially damaging in peat-based media are therefore less likely to be damaging in a mix containing compost. For example, an EC of 600 µS/cm (1:5 extract) would be of concern in a peat mix but could be acceptable in a peat/compost blend. Previous and current relevant work Maher et al. (2001) researched the use of compost in growing media and found that the rise in the EC of a growing medium from the addition of compost could largely be off-set by reducing the potassium fertiliser addition to the peat it was blended with. Other work (Mazuela et al., 2012) has shown that the EC of a growing medium containing compost in grow bags can be reduced by saturating with a nutrient solution which has a lower EC than the compost does, before using it to grow crops. The above mentioned studies were the only ones relevant to this report, but neither study was conducted on PAS100 composts, let alone composts produced according to the WRAP Guidelines for the specification of quality compost for use in growing media (WRAP, 2011a). Their conclusions therefore have limited relevance to this project. Extent to which issue has been resolved Nearly all the growing media manufacturers surveyed in this project thought that the inherent high EC of compost was an issue that restricted their use of some composts and also restricted the amounts that they could safely use in growing media products. They deal with the problem of high EC in compost by avoiding composts with an EC greater than 1000 µS/cm and limiting the inclusion rate of compost in the mix. One compost and growing


media producer said that avoiding too many grass clippings in the feedstock helped to reduce the EC of the compost. It was noted by a further manufacturer that minimising the amount of food waste in the feedstock helps to control high EC in the compost. Guidance to this effect is given in WRAP 2011b. The WRAP Specification (2011a) recommends that compost for use in growing media ideally has an EC of less than 600 µS/cm with an upper limit of 1500 µS/cm (1:5 extract). In practice, not many composts have values of less than 600 µS/cm. A commonly quoted solution to compost with high EC is dilution with low EC materials such as peat, coir or bark when formulating the growing medium. Recommendations for minimising the impact of the issue in future The impact of EC is minimised in practice by limiting the rate at which compost is used in growing media and using low EC materials as diluents. The impact of EC can more easily be reduced during manufacture of growing media if the EC is consistent between batches of compost so that growing media manufacturers can make easy, small adjustments to fertiliser additions. Green/food composts tend to have higher EC values than green composts and for this reason, they may have to be included at lower rates. The two WRAP guides (WRAP 2011a and b) provide clear information as to target values for compost EC and on methods for achieving these values. It is important to ensure that compost producers producing, or interested in producing composts for use in growing media know about these publications and have read and understood them.

3.2.5 Weed seeds Introduction One issue of concern raised by the Sustainable Growing Media Task Force was the possibility of weed seeds from the input materials remaining viable after composting. BSI PAS100 and the WRAP Good Practice Guide (WRAP 2011b) states that weed seeds and propagules should be absent and a weed test is part of the suite of analyses for PAS100. Generally the composters’ response to the questionnaires was that the presence of viable weed seeds in compost was not an issue. Growing media manufacturers who used green compost in their mixes generally also said that weed seeds were not an issue. Manufacturers who don’t use green compost however did feel that weed seeds were an issue. Of the professional growers who replied, all felt that the presence of weed seeds was an issue which would prevent or may limit their use of green compost. If it can be clearly demonstrated that weed seeds are killed at or below temperatures achieved during the composting process, then this will go a long way to reassuring prospective purchasers of compost that weed seeds have been eliminated. Previous and current relevant work Researchers from many countries have studied the viability of weed seeds in relation to temperature; for example in Japan, Nishida et al. (1999) studied the survival of ten upland weed species at 55 and 60oC and found that nine of the species were killed by exposure to 55o C for 72 hours and at 60o C for 24 hours. The remaining weed species was killed after exposure for 120 hours at 55oC and 30 hours at 60oC. Egley (1990) at the Weed Science Laboratory at Stoneville, Mississippi, USA heated a range of eight weed seeds in soil in pans using a range of temperatures between 40 and 70oC for up to 7 days in either dry (2%) or moist (19%) soil. In moist soil there was enhanced kill of seeds with practically all seeds non-viable after 3 days at 60oC. It took up to 7 days at 700C for complete kill of the seeds in dry soil. Soil moisture content clearly influenced weed seed kill: under dry conditions seeds can survive better. Green compost after maturation typically has a moisture content of around 40% and it almost always has a higher moisture content (typically 50-65%) during the active composting process, during which time the majority of pathogen and weed seed kill will take place.


In Canada there have been a number of studies which added weed seeds in nylon bags to cattle manure composts in windrows at different depths and looked at seed viability after different time intervals. Tompkins et al. (1998) placed seeds of 12 weed species in muslin bags at either 0.3 or 1.0 metre depths in windrows of cattle manure being composted. After 2 weeks composting, most seeds were non-viable and after 4 weeks’ composting at 55-650C the viability of all seeds was zero. Weed species used were common and included wild oat and hemp-nettle. The authors recommended sheeting the composted manure with tarpaulins to stop weed seeds from blowing on the weed-free composted manure. Larney and Blackshaw (2003) studied five weed species, again using bags placed in beef cattle manure compost in open air windrows. A temperature above 60OC was required to kill all weed species, although some were non-viable above 390C. They concluded that factors other than temperature may play a role in eliminating weed seeds, for example, chemicals present in the compost. In Florida, Ozores-Hampton et al. (1999) studied immature municipal separated solid waste composts of varying ages from 3 days, 4 weeks, 8 weeks and a matured one year old compost. Extracts were taken using distilled water and added to Petri dishes with seeds of both weed species and maize. The greatest decrease in seed germination was noted with 8-week old compost and the least with the 1 year old compost extract. Further work with 8 week-old compost using 14 weed species was undertaken and the petri dishes incubated in the dark at 27OC for 8 days. Seeds of nine of the fourteen weed species studied were either unable to germinate, or showed very low germination. The authors concluded that chemical exudates from the immature compost, particularly volatile fatty acids such as acetic acid, were responsible for lack of seed germination. The concentration of acetic acid reduced a hundredfold between 8 weeks and 1 year. This suggests a further means by which composting can reduce the viability of weed seeds present. Finally, Grundy et al. (1998) at Wellesbourne, studied the seeds of eight weed species, which were buried in moist compost in mesh bags at three different temperatures for 3, 21 and 84 days. This work was done specifically to address concerns of potential contamination by weed seeds either wind-blown from nearby fields or coming in via the plant material in feedstocks. Mature compost was placed in 80 litre bins controlled at 35, 45 or 55oC. Moist air was blown in to stop the composts drying out and moisture content was kept around 40% (a typical value found in composts during the maturation stage). Eight weed species, including annual meadow grass, black nightshade, prickly sow-thistle, chickweed and common speedwell, were mixed with compost and placed in the mesh bags in the composts in the bins. Samples were removed at intervals as above and seeds placed in petri dishes, sealed and incubated. Germination was compared with seeds which had not been placed in contact with the compost. At 55oC, none of the eight weed species germinated or appeared to be viable even after just 3 days. The authors concluded that as long as all parts of the windrow reached 55oC for three days all weed seeds from the range studied would be destroyed, assuming no influx of seeds after the windrow has started to cool. Some of the weed species in the trial germinated at 35oC even after storage for 84 days. It was concluded that any viable weed seeds found in compost are likely to have survived due to insufficiently high temperatures in the windrows or may have blown in on the wind after the compost has begun to cool. Extent to which issue has been resolved Results from many studies around the world have shown that weed seeds will not germinate when exposed to temperatures of 55-60oC for as little as 3 days. Temperatures during the sanitization phase of composting typically reach levels of at least 60oC. Turning the compost will allow all parts from the hot core to the cooler outer extremities to mix and enable the whole windrow to reach the desired temperature as required by the composter’s Standard Operating Procedure. PAS100 guidelines recommend that a temperature of 65oC should be


achieved for 7 (not necessarily consecutive) days throughout the compost in order to eliminate pathogens and weed seeds. It is also recommended that compost moisture content is maintained at or above 51-65% (m/m) during the sanitisation phase and 40-65% (m/m) during the stabilisation phase to maximise kill of weed seeds, human and plant pathogens. In addition, there is evidence that chemicals such as volatile fatty acids released by immature composts can impact (along with high temperatures) to further reduce the viability of weed seeds. Providing maturing composts are covered as they cool down or composting is enclosed, weed seeds should not be a concern when using green compost to make growing media. In-vessel composting and maturation in buildings would go a long way to eliminate the likelihood of weed seed contamination. Likewise at delivery to the growing media manufacturer, green compost, just like any other material should be stored under cover and surrounding areas kept weed-free. Data collected by ORG between 2004 and 2008 showed that in a survey of 130 samples in excess of 90% were free of weeds, indicating that composting at the correct temperatures will eliminate weed seeds (K Zennaro, personal communication). It is important to note that some instances of contamination of compost by weed seeds are thought to result from weed seeds blowing on to the compost after it has been sanitised. Compost producers must consider all possible reasons for weed seed contamination of composts when they are developing their standard operating procedures for PAS100. The compost producers who were also manufacturers of growing media and who replied to the questionnaire all said that weed seeds were not a problem in the production of growing media that included green composts due to the temperatures achieved during the composting process. Some of the manufacturers who would not use compost in their growing media said that the possibility of viable weed seeds being present prevented them from using green compost. However, they also said the same about most of the other potential issues raised in the questionnaire. Professional growers were divided over the issue of weed seeds, some seeing this as an issue which prevented them using green compost and others saying that it was not an issue. Recommendations for minimising the impact of the issue in future Standard composting times and temperatures are sufficient to render weed seeds non-viable. Contamination of compost could still occur from wind-blown seeds as the compost cools down during stabilisation and maturation. To minimise this possibility, composts should either be matured under cover or at the least outdoor windrows should be sheeted for the composts used to supply manufacturers of growing media. Windbreaks placed upwind of the prevailing wind (or winds from directions likely to blow seeds in) may reduce the inflow of seeds to the composting site. All compost sites should control weeds as far as is practicable and in any event they should prevent weeds from producing seeds that could be blown onto compost windrows. The two WRAP guides (WRAP 2011a and b) provide clear information as to how to eliminate weed seeds from composts. It is important to ensure that compost producers producing, or interested in producing composts for use in growing media know about these publications and have read and understood them. A further option would be to require compost producers to actively demonstrate the phyto-sanitary robustness of their composting processes. This could be achieved by introducing ‘captive’ indicator organisms (such as weed seeds or selected plant pathogens) at the beginning of the composting process, and retrieving them for testing at the end of the process. The Animal Health and Veterinary Laboratories Agency (AHVLA) adopt a similar


approach for demonstrating pathogen kill when composting processes seek approval to handle animal by-products such as household food waste.

3.2.6 Sciarid flies and other pests Introduction Sciarid flies (Bradysia difformis), also known as fungus gnats, and shore flies (Scatella tenuicosta) are widespread and important pests of protected ornamental and bedding plants, herbs and nursery stock propagation (Chandler, 2007; Sumption and Lennartsson, undated). The larvae of sciarid flies feed on organic matter in the growing medium (such as wild fungi and decaying plant material) but they also feed on plant roots and inside stems, which can cause plant death and reduces crop quality. The adult flies can also act as vectors of plant pathogens such as Pythium and Phytophthora species. Shore flies feed on algae and can also transmit plant diseases and are a particular problem on potted herbs, causing supermarket rejection as well as nuisance to workers in the nursery. Biological control of sciarid flies has been successfully used in the mushroom industry for many years by using agents such as Hypoaspis species mites and the nematode Steinernema feltiae. Neither of these biocontrol agents is effective against shore flies. The predatory rove beetle Atheta coriaria has been found to be effective against the eggs and larvae of both sciarid and shore flies but require breeding boxes to release them, and close control of feed in the boxes. The three biocontrol agents are available to professional growers and the mites and nematodes are also available to amateur gardeners by mail order. Lindquist (1992), cited by Chandler (2007), found that sciarid flies occurred at their highest numbers in growing media with high microbial activity such as green compost, and at lowest numbers in older peats, with low microbial activity. Binns (1977) found that sciarid flies prefer fungal material and also high levels of nitrogen (including ammonia) from organic fertilisers. Organic slow release fertilisers such as hoof and horn meal are frequently added to peat-free growing media, which is likely to further attract sciarid flies. Previous and current relevant work Replies to the questionnaire from several professional growers indicated that sciarid flies are attracted to growing media containing green compost and this would prevent them from using the material. Manufacturers of growing media either felt that this issue limited inclusion or prevented them using green compost. One growing media manufacturer cites sciarid flies being the main complaint (from amateur gardeners) about their range of peat-free products, and they provide specific watering advice (on the bags) to keep the surface dry, and not overwater. Producers of compost generally felt that this was either not an issue or it had been in the past but now was not. At least two compost producers have successfully used Hypoaspis species mites at the end of the composting process as a control measure before delivery to the growing media manufacturer. Some commented also that it was important to keep the compost dry and under protection and ensure that it wasn’t immature (since ammonia, which is present at higher concentrations in immature composts, is a known attractant of sciarid flies). One manufacturer who uses a lot of green compost in their mixes felt that part of the problem was overwatering from above (by retail customers) which would encourage flies to come in and lay eggs in the damp surface. Another manufacturer who uses considerable amounts of green compost felt that research is required to develop techniques or products to make green compost less attractive to sciarid flies.


A search of the literature has come up with a small number of references which may be of help regarding discouraging sciarid flies from growing media in general, including media containing green compost. Olson et al. (2002) in the USA studied the emergence of sciarid flies in sterilised and unsterilized coir and peat at a range of moisture levels between 15 and 90% and also amended the two growing media components to produce fine, medium and coarse mixes. The work showed that sciarid flies did not emerge from either coir or peat unless an attractant (yeast) was present. Sterilising the growing media did not make any difference either. Moisture content did not affect emergence in coir across all rates of moisture content and for peat the 15% and highest moisture contents produced fewest flies, the 52% moisture content producing most. The authors suggested that manipulating the texture and moisture content of growing media may be a means of slowing down the build-up of sciarid flies. Plant growth was not affected by the treatments which minimised sciarid fly emergence.

Cloyd et al. (2010) studied the repellence of commercial fabric softener dryer sheets (Bounce® Proctor and Gamble) to sciarid flies under controlled conditions in compartments. It had been observed that carrying the dryer sheets in a top pocket repelled mosquitoes and was used by professional gardeners in the USA for that purpose. Five experiments were undertaken, using compartments with and without sheets present; some experiments included a commercial growing medium with and without sheets present. Overall, sciarid flies were reduced by two thirds across all treatments which showed the repellency effect. Analysis of the sheets showed the presence of Linalool (3,7-dimethyl-1,6 octadien-3-ol) a monoterpene alcohol used in the perfume industry. This chemical is found naturally in plants such as lavender, marjoram and basil and is known to be toxic to some mites and insect pests. The second chemical found was citronellol, (3,7-dimethyloct-6-en-1-ol) another monoterpene alcohol which produces a lemon scent and is known to be repellent to mosquitoes. This chemical is found naturally in a number of plants. The authors suggested that sheets of the fabric softener could be placed in containers near plants in glasshouses in order to deter sciarid adults and thus stop egg laying and reducing larval populations. The above two potential control measures could be studied in the future, looking at growing media texture and moisture, and looking at certain chemicals of plant origin which may be help to deter sciarid flies. Due to the rapid breeding cycles of sciarid and shore flies, total elimination of these pests is unlikely to be feasible. Extent to which issue has been resolved Two of the compost producers surveyed have successfully added Hypoaspis species mites to green compost before despatch to growing media manufacturers, and they have reported that this has been a successful control measure. However, absence of sciarid flies at manufacture and delivery to the nursery or garden centre will only be sufficient for initial potting of plants, and further applications of biocontrol agents would need to be made for ongoing control, which is not a cheap option. Hygiene at the nursery and attention to watering will also be required in order to keep this pest to a minimum. One compost and growing media producer stated that sciarid flies were an issue in the past but were now no longer an issue, and they were one of the composters who added Hypoaspis species to some of their professional growing media mixes. One UK producer of both composts and growing media felt that sciarid flies were at least an occasional problem which may be due in part to using not fully matured compost. Another stated that sciarid flies were not a problem provided that the compost was fully stabilised and that tighter standards than PAS100 for sampling and checking maturity needed to be in place - see WRAP (2011 b) for additional maturity requirements. Certain chemicals in green compost,


e.g. ammonia, are known attractants of sciarid and other flies, so ensuring maturity before use will undoubtedly help. Instructions to growers and advice on retail bags regarding watering would also help by ensuring that the surface of the pot or seed tray is kept dry by using smaller amounts of water more often and allowing the surface to dry out between waterings, and watering from below if possible (reply by a compost manufacturer who also produces growing media). Recommendations for minimising the impact of the issue in future Compost producers need to consider covering windrows, which would help to keep compost dry and not exposed to sciarids. Maturation under cover in buildings would be a better option. Shore flies live on algae, so keeping the composting site free from standing water is important. Dosing matured compost with Hypoaspis mites as a biocontrol measure will control sciarid fly larvae and eggs, but not shore flies. Professional growers and also amateur gardeners could adopt the following measures to minimise sciarid and shore fly breeding:

Keep areas under benches and gutters free from algae and puddles;

Don’t water plants from the top; watering pots and trays from below will keep the

growing medium surface dry;

A layer of sand or fine vermiculite on top of the growing medium will help to discourage

egg laying by sciarid flies (Binns 1977); and

Applications of biocontrol agents Hypoaspis species and Steinernema feltiae will destroy

larvae. These products are also available for retail purchase but price may be a limiting

factor. Atheta (rove beetle) is also effective, but due to requirements to inspect breeding

boxes and replace pelleted feeds this would currently be suitable only for professional

growers.

The following future work should be considered:

Investigate the interaction of growing media, particle size and watering regime to control

flies.

Determine the effect of attractants e.g. yeasts, organic fertilisers impregnated on sticky

traps to lure flies.

Further study of natural plant products such as Linalool and Citronellol to repel sciarid flies

from around plants and suitable delivery systems including impregnated tissues.

3.2.7 Compost shelf life Introduction The shelf life and storage characteristics of growing media containing green compost are very important because products, particularly retail growing media products, may be stored for up to 12 months between manufacture and use. Changes to the physical, chemical or biological properties of the products during storage can have negative effects on plant growth (Surrage & Carlile, 2009). Retail products may also be rejected by consumers if they appear to be contaminated with fungal growth (even if the fungus is actually harmless to plants). The basic requirement for good shelf life is for the product to be chemically stable/mature. If active composting occurs after a compost has been incorporated in a growing medium, it will have a negative effect on plant growth (Raviv, 2011a). Biological processes occurring in a growing medium after manufacture can cause various problems (Verhagen, 2007) including:

loss of volume and particle size change (reduction in air-filled porosity, which can lead to

a lack of air around plant roots);

nitrogen immobilisation (which will results in less nitrogen for crops);


formation of phytotoxic compounds;

formation of water repellent colloids;

increase in pH (leading to decreased plant availability of most trace elements and

phosphate);

change in Cation Exchange Capacity (CEC, which may mean that nutrients are held less

strongly within the medium and are more easily leached);

increase in salinity due to mineralisation (which can adversely affect plant roots); and

reduced shelf-life due to the above phenomena.

There is some contradiction between different requirements because composts with high biological activity are undesirable for use in growing media, due to competition with roots for oxygen and possible nitrogen immobilisation, yet compost disease suppressiveness is a biological phenomenon and requires microbial activity (Boulter-Bitzer et al., 2006). Most growing media manufacturers currently using compost in their products do not regard shelf life as a barrier to the use of compost in growing media (some have never considered it a problem), although it was cited as an issue by the manufacturers who are not using it. Previous and current relevant work Early research by WRAP (WRAP, 2005) indicated some problems with storage of non-peat growing media but these have largely been overcome. In the above project, the storage stability of retail growing media based on green compost was evaluated in a 12 month storage trial. The trial simulated commercial conditions as closely as possible: treatment mixes were prepared and bagged using modern production facilities, then palletized prior to storage outdoors. The project compared peat-free, peat-reduced and all-peat mixes, included two peat types (Irish and Finnish), two alternative substrates (matured forest brash and matured bark fines) and two rates of mature PAS100 certified green compost (20% and 33% v/v). Representative, replicated samples were taken at bagging (time 0) and after 1, 3, 6 and 12 months of storage. Samples were tested for ammonium nitrogen, nitrate nitrogen and other water-extractable nutrients, and were subjected to two stability tests: nitrogen drawdown index (NDI) and the Dewar (self-heating) test. At sampling, no bad odours, flies or weeds were encountered in any treatment and obvious fungal growth, although occasionally observed in all treatments, was insignificant. All mixes started with a similar amount of nitrogen (N) fertiliser. The key change observed was immobilisation of water-soluble N (also known as ‘lock-up’ or ‘drawdown’), as evidenced by reductions in levels of ammonium N and nitrate N, which varied markedly with treatments. Losses of available N were highest in green compost-based mixes, especially in the peat-free formulations, where both bark fines and brash were present, and almost as high in the two Finnish peat plus green compost mixes. By contrast, even at 12 months, N losses in the 100% Irish peat mix were virtually nil. Where Irish peat was mixed with 20% v/v green compost, losses were small but, where mixed with 33% v/v green compost, they were marked. After 12 months, only three of the eleven mixes evaluated were considered fit-for-purpose, namely, 100% Irish peat, Irish peat plus 20% green compost and 100% bark fines. The project recommended the evaluation of the use of slow-release N sources in growing media containing green compost and the inclusion of such sources is now common practice. In a separate trial, the storage properties of peat-free growing media containing green compost were studied in the UK by storing media with increasing percentages of green compost for 12 months under different conditions (Surrage & Carlile, 2007). These trials showed that the bulk density, organic matter content, pH, electrical conductivity,


ammonium-N, magnesium, calcium, zinc and manganese concentrations remained fairly constant over 6 months, with some variation in nitrate-N levels and an increase in available phosphorus concentration (presumably due to release of available phosphorus from the mineral component of the green compost over time). A dehydrogenase activity assay indicated some activity in the mixes containing green compost in the initial month but then a decline in microbial activity during the 6 month trial. Work in Ireland (NiChulain & Prasad, 2007) looked at different methods of evaluating the stability of green compost intended for use in growing media. The three methods tested were the Dewar self-heating test, the ‘Solvita’ TM test (which is based on the evolution of CO2 and free ammonia) and a pressure sensor method (OUR/Oxitop) which measures the uptake of oxygen and hence the biological activity of the material. The Dewar self-heating test only really distinguishes between very mature and very immature compost so was not considered precise enough. The research recommended the use of the oxygen uptake rate (OUR) method for determining the stability of compost for use in growing media. The standards body in The Netherlands (RHP) has also researched stability (and hence shelf life) of growing media and the OUR method has been adopted. The standard for respiration of green compost for use in growing media in The Netherlands is <15 mmol of oxygen per kg of organic matter per hour. WRAP published guidelines for compost to be used in growing media (WRAP, 2011a), which include guidance on compost maturity and stability. A C:N ration of 15 (not greater than 20) is recommended and a Nitrogen Drawdown Index of 1 (not >0.7 ideally). In addition to this, some growing media manufacturers use the ‘Solvita’ test for maturity and specify a score of 7 for compost to be used in growing media products, which is the score typically achieved by mature compost. Extent to which issue has been resolved Storage characteristics and shelf life do not appear to be a major barrier to the use of green compost in growing media at current inclusion rates (typically 10-30%). Respirometric methods have been shown to be good for assessment of biological activity and a CEN (European Committee for Standardisation) method using CO2 evolution/O2 uptake is proposed as a European standard. The storage conditions under which composts and growing media are kept (both composts prior to incorporation into growing media and post-manufacturing) are important, however. Shrink wrapping pallets is not recommended since this can restrict the amount of oxygen which can get into the compost or media and storage conditions must not be too cold (not below freezing) or too hot (e.g. storage within glasshouses is not ideal [anonymous industry expert, personal communication]). Screened compost must be turned prior to bagging to prevent it becoming anaerobic and the finer the grade of compost the higher the risk of anaerobic conditions occurring.

One of the growing media manufacturing respondents to the questionnaire did not consider shelf-life of compost a problem as long as the storage conditions of the end product were right. They also commented that incorporation of an appropriate slow release nitrogen fertiliser avoids the problem of depletion of nitrogen reserves in the product during storage. Recommendations for minimising the impact of the issue in future Shelf life is not a major issue if strict quality control measures are followed in relation to compost stability, so that only mature composts are used and they are consistent from batch to batch. Details on how to achieve good compost shelf life are provided in WRAP, 2011a and b. It is important to ensure that compost producers producing, or interested in


producing composts for use in growing media know about these publications and have read and understood them.

3.2.8 Compost consistency Introduction Several authors have reported that lack of consistency of composts is a key/major problem in relation to their use in growing media (Carlile, 2008; Mazuela et al., 2012; Prasad & Maher, 2001; Surrage, 2007; Surrage & Carlile, 2008). Some of this work was undertaken prior to the widespread accreditation of composts to PAS100 (e.g. Prasad & Maher, 2001), but most of it does relate to PAS100 composts. Composts have been reported to vary both within UK sites (between batches) and between UK sites (Wallace, 1999, WRAP, 2005) and consistency of composts does remain a barrier – whether perceived or not. Several of those who responded to the request for their views in this project felt that lack of compost consistency either prevented them from using composts in growing media at all, or prevented them from using more of it than they did in manufactured growing media. Compost characteristics can vary both within a particular composting facility (for example, between batches across the course of a year) and between composting facilities. The former is of concern to users requiring small quantities of compost from a single site, as they cannot be sure that compost performance will be consistent. The latter is of concern to users requiring larger quantities, who may source compost from more than one supplier. There is an acknowledgement amongst some scientists and growing media manufacturers that with careful choice of feedstocks and process control, compost producers can maximise the quality and minimise the variability of their products in order to satisfy the requirements of growing media producers (Surrage, 2007; Raviv, 2011a). Relevant work, the current situation within the industry in relation to this topic and recommendations to minimise the impact of the issue in future are discussed in the following sections. Previous and current relevant work Shortly after the BSI PAS100 specification for composts was first produced in 2002, the DETR cited that compost variability was a key barrier to widespread use of composts in the horticultural sector (DETR, 1998). For this reason, WRAP commissioned a study in 2003 to examine the nature and extent of compost variability over a 12 month period (WRAP, 2005). Finished compost and feedstock from nine composting sites were sampled and tested for a range of quality parameters monthly for 12 months. Most of these composts were PAS100, whereas others were working towards PAS100 accreditation.

Feedstocks were tested for dry matter content, chloride, total potassium (K), carbon (C), nitrogen (N) and C:N ratio. Finished composts were tested for a wide range of parameters including:

Physico-chemical parameters:

Bulk density

Dry matter and moisture content

pH

Electrical Conductivity (EC)

Chemical parameters

Water extractable

Chloride

Nitrate-N (NO3-N), Ammonium-N (NH4-N) and the ratio between them, total N, total

C and C:N ratio


Phosphorus (P), K, Magnesium (Mg), Sodium (Na), Boron (B), Manganese (Mn)

CAT extractable

P, K, Mg, Na, B, Mn

Total N, C, P, K

% Loss on ignition

Volatile solids content

Physical contaminants

Plastic

Glass

Metals

Stones

Microbial parameters

Carbon dioxide (CO2) evolution.

The total weight of stones (> 2 mm) was reported for the months March to July inclusive; from August onwards, stones from 2-4 mm and stones > 4 mm were reported separately. Physical contaminants were only reported for the first four months. The project showed that there were some pronounced seasonal variations in the characteristics of the feedstocks tested. Nitrogen and K concentrations were higher during spring/early summer, when greater quantities of green, leafy materials were accepted for composting. Carbon concentrations were higher during autumn/winter when a greater proportion of leafless, woody materials were accepted for composting. There were no great differences between different green waste feedstocks (i.e. kerbside v civic amenity site). Seasonal variations in feedstocks did not necessarily translate into variations in compost quality. Total C and N concentrations were consistent within sites over the course of the year, despite there being pronounced seasonal variability in these parameters in feedstocks. Potassium levels did show a degree of variation, but local climatic factors may have played a role in this. Many compost parameters showed no significant geographic variation across sites or seasonal variation within sites. Site specific factors, such as screen size, maturation period and storage arrangements were thought to have had the greatest impact on compost variability. Having looked at all of the processes from which samples were taken during the project, the authors of the study felt that compost producers who maintained a consistent composting process regime produced more consistent composts. Process management was thought to play a critical role in reducing product variability. The following practices were reported as likely to help maintain product consistency:

increasing the length of time that composting is actively managed;

increasing maturation period;

storing finished compost under cover;

using microbial respiration assay to ensure composting is complete; and

ensuring composting process parameters (turning regimes, active composting periods

etc.) are consistent over the whole year.

In general, the composts tested in the WRAP project were found to have performed well against the growing media specifications of the time (WRAP, 2004a), particularly those composts aimed at the growing media market. All composts met the guideline value for pH, and most of the composts were within or close to the guideline values for EC. Extending the maturation period was thought likely to result in composts with lower EC. All of the composts


met the guideline values for contaminants and most also met with guideline values for chloride, sodium, stone content, moisture content and bulk density. There was no evidence of significant geographical differences between composts made from green wastes. There were slight differences in the levels of a few elements (including Cl and Mg), but this variability was no more than that found in different batches of composts made at the same site. The composts tested were largely from composters supplying other, less stringent markets such as agriculture. Variation in composts working to the WRAP spec guides is unknown but may be less. More recently, Surrage and Carlile have conducted work, based at Nottingham Trent University, to investigate the variation in quality of composted green wastes and to suggest ways by which the consistency and quality of composts can be improved. The work is reported in greatest detail in Surrage’s PhD thesis (Surrage, 2007). This comprehensive piece of work included studies on the nature of green waste treatment/recycling in the UK, the storage properties of peat-reduced media, and the performance of peat-free growing media as well as work on the variability of composts. It is important to place the work in context: it was conducted during the years 2004 to 2007 (as was the WRAP project discussed above), during a period when the UK composting sector was still in a phase of fairly rapid development. The study tested 15 samples of green compost, but there was no indication of how many of these were PAS100-accredited or working towards accreditation, and limited information was provided on the feedstock collection method, the exact list of feedstocks from which each was made, or the composting system by which each was produced (e.g. process duration, sanitisation criteria etc.). The fifteen samples came from twelve different compost producers (including both local authority and commercial producers) located throughout England. Samples were tested for: bulk density, organic matter content, ash content, moisture content, pH, electrical conductivity and total N, P and K content. Considerable variation was found between samples for every parameter tested. This variation was thought to be due to wide variations in feedstock types, feedstock collection methods and to differences in composting processes. Surrage pointed out that the quality of one of the products tested was particularly high and that this quality was likely to be due to the care taken to select appropriate feedstocks and to design and manage an appropriate composting process. She suggested a range of measures which could be taken in order to improve the consistency of all composts intended for the high value growing media market, where both quality (in terms of both safety and useful horticultural characteristics) and consistency is vital. The measures suggested included:

development of best practice guidance in composting (e.g. the Composting Association

Code of Practice, 2005) and dissemination of best practice guidance amongst

practitioners. This guidance should include information on:

source segregated green waste collections (essential in PAS100 composting

processes);

blending of feedstocks in order to obtain an appropriate C:N ratio for optimal

composting; and

longer composting processes for composts intended for use in growing media;

standardisation of best practice throughout the composting industry including:

adherence to the requirements of appropriate best practice guidance;

adherence to the requirements of and accreditation to PAS100:2005 (which has since

then been superseded by PAS100:2011).


In his work at Horticulture Research International (HRI) at Warwick on the RECOVEG project (Recycling horticultural wastes to produce pathogen suppressant composts for sustainable vegetable crop production), Noble showed that the results of scientific work to determine composting best practice could be applied to industrial scale processes in order to produce commercial quantities of high quality composts with predictable characteristics (Noble, 2005). In his recent review, Raviv (2011a) felt that the variability of both nutrient content in composts and nutrient availability from composts merited further scientific study, since better understanding of the subject would help growers to optimise plant nutrition and minimise nutrient leaching. He also recommended the formulation of rigid quality control measures for composts intended for use in growing media. There are a number of controls in place to ensure that compost ‘quality’ and safety are high in the UK. Similarly, there are several controls in place to make sure that composts are applied in order to provide benefits to agriculture, soil-grown horticulture and landscaping without harming humans, wild or domestic animals, crops, amenity vegetation or the environment. These controls, which take the form of legislation and guidance, are summarised in Section 3.3. In fact, most of the controls documented in that legislation and guidance relate to safety rather than quality (as defined by compost users). Compost producers must therefore find ways of maximising all aspects of product quality and must document the results from testing appropriate parameters additional to those required by PAS100 in order to satisfy customer requirements. For example, parameters such as total nutrient content and nutrient availability are of interest to growing media manufacturers but are not required under the PAS100 specification. ORG (under their old name, AfOR), has worked hard to improve the quality and consistency of composts during the past decade. In 2002, the first version of BSI PAS100 was produced (see Section 3.3). The scheme provided a baseline quality standard for compost and ensured that compost producers certified through the scheme manufactured a product that was consistent, safe and reliable to use. It also provided a foundation upon which producers could further develop their compost products. It was revised and republished in 2005 and again in 2011, when the upper limits for physical contaminants were reduced in response to requests from some industry stakeholders, and the increased ability of compost producers to meet these lower limits. The quantity of feedstock recycled through composting and accredited through the UK compost certification scheme is steadily increasing and it is estimated that in 2010 48% of feedstock which was treated through composting was treated by sites compliant with or having applied to join BSI PAS100 (WRAP, 2010). The percentage of feedstock treated in Scotland at sites compliant with or having applied to join BSI PAS100 is thought to be much higher, due to work by Zero Waste Scotland to reduce volumes of organic waste to landfill and encourage PAS100 certification of Scottish composting sites. In Scotland, compost produced to BSI PAS100:2011 is considered a product rather than a waste and is therefore not subject to waste management licensing regulations. In England, Wales and Northern Ireland, compliance with the Compost Quality Protocol (CQP) is also required if compost is to be classed as a product (rather than a waste). The CQP builds on BSI PAS100:2011 and clarifies which waste materials can be used in quality compost production, reinforcing traceability throughout the production process by ensuring accurate record keeping. Together, the BSI PAS100 standard, the CQP and the requirements of the Animal By-Products Regulations (all described in more detail in Section 3.3) have helped to improve considerably the safety and quality of composts since their initial publication (starting in 2002) (K Zennaro [ORG], personal communication). Although there have been no


further published studies on the consistency of UK compost products in terms of their variability within and between sites, there is clear evidence that increasing numbers of producers are achieving the revised (stricter) standards for physical contaminants set out in PAS100:2011. In 2005, The Composting Industry Code of Practice was published (The Composting Association, 2005). It dovetailed with the requirements of PAS100 and amongst other things, it aimed to:

identify good site management practices that could act as a benchmark for industry and

regulatory authorities; and

provide greater confidence in the composting process and end product (presumably since

it aimed to help compost producers develop effective, consistent composting processes).

Whilst it was recognised during the first few years of the 21st century that the BSI PAS100 specification, the CQP (in England, Northern Ireland and Wales) and the Animal By-Products Regulations were all helping compost producers to focus on the development of composting processes which could result in the production of safe, quality, general purpose products, there was still a lack of guidance for compost producers as to how best to produce specialist composts for high value markets such as growing media. The WRAP specification and guidelines are therefore of particular value in this respect (WRAP 2011a and b). Extent to which issue has been resolved The stakeholders interviewed as part of this project were divided on whether they felt that consistency of PAS100 composts was an issue for them. In brief, of the ten responses obtained from compost producers and growing media manufacturers (some of whom were also compost producers), one said that compost consistency had never been an issue for them, three said that it had been an issue but was not any more, two said that it limited their use of PAS100 composts for growing media production and three said that it prevented them from using composts in growing media (one did not respond to the question). Of the eight growers interviewed, six said that lack of compost consistency was a key reason why they did not want to use growing media based partly on composts in their production system. The remaining two growers interviewed did not respond to the question. Of the two major retailers interviewed, one said that their company did not sell growing media containing green compost, because they believed that all nine of the issues addressed in this project (including consistency of composts) remained a problem. The other simply did not have confidence that CIGM could perform as well as other types of amateur growing media. The second felt that compost consistency was one of the issues which continued to limit their sales of (CIGM). One compost producer and growing media manufacturer who felt that his company had largely solved the issue of compost consistency had strong opinions on the subject. He felt that it was perfectly possible to make good, consistent compost products for use in CIGM providing the entire process from feedstock selection and preparation to product preparation was managed with care and attention to detail. He felt strongly that some compost producers could improve the consistency of their products through more careful management of their processes and that the perception of poor consistency of both composts and CIGM related more to earlier bad experiences (their own or those of colleagues) than to experiences of the best recently produced composts/CIGM. It is clear that although some stakeholders felt that the issue of poor compost consistency has been solved, many do not, and there is a widespread perception amongst both growing media manufacturers and growers that compost consistency (and therefore the consistency of CIGM) remains an issue. More work therefore needs to be done to address the issue.


Recommendations for minimising the impact of the issue in future Between them, four major growing media manufacturers said that the following were particularly important when trying to improve consistency of composts for use in CIGM:

careful selection of input materials; for example, tightening of control over the C:N ratio

in feedstocks going forward for composting (by mixing of green and woody substrates to

get an ideal blend with appropriate moisture content);

Very careful management of the composting process in line with best composting

practice, to ensure good aeration, appropriate moisture content and perhaps more

frequent turning;

Effective screening, using good quality machinery at the end of composting to remove

large woody fragments;

Investment in frequent testing (both during AND after the composting process) and

blending facilities to allow mixing of different batches of compost in order to improve

characteristics of batches and consistency of batches throughout the year; and

Investment in a longer composting process than that required for composts intended for

use as soil conditioners, with covered composting areas for sanitisation, stabilisation,

maturation (and storage prior to sale if required), better management, greater scale of

production.

If compost producers were to implement all of the points listed above in order to maximise compost consistency, they will clearly spend more money than they would operating a basic process intended to make good quality, safe composts for use as soil conditioners. However, some compost producers and growing media manufacturers have said that it is possible to balance this extra cost through extra revenue gained from sales. Although there is some evidence that the above points will help compost producers make better, more consistent products, and there is good guidance available to help them achieve best practice (WRAP, 2011a; 2011b), there is still a serious problem in terms of the perceptions of both growing media manufacturers and growers that composts and CIGM are not consistent. For that reason, several approaches are recommended. Firstly, the WRAP good practice guidance (2011a; 2011b) should be promoted more widely. Rather than only being available online, it should be printed and sent to all compost producers who are known to sell into high value markets (e.g. turf production, turf management and growing media) with a covering letter. It may also be a good idea to run two dedicated seminars (in both the North and South of the UK) for compost producers interested in selling to the growing media market. The WRAP guidance could be promoted, and the difference in mindset required for top quality compost production explained in detail. It is worth noting that only half of the growers who responded to the survey were aware of the WRAP guidance. Whilst most growers now buy in their growing media and rely to a large extent on their growing media supplier to recommend the best products for them, several were interested to learn about the guidance and were interested to hear of the significant improvements currently being made in the quality of both green compost and CIGM. For the above reason, there is also a need for further work to demonstrate the performance of CIGM on nurseries. Although there has been a considerable amount of (mainly WRAP-funded) work (e.g. WRAP, 2005c; 2006a; 2006b; 2007; 2008; 2009) done on nurseries in the past, some of it has been conducted over relatively short time-scales with limited technical input from those (trained in experimental work using growing media on nurseries) who really understand growing media, CIGM in particular and how to use CIGM to best effect. There is a clear need for simple trials to be conducted on the nurseries of growers


who are genuinely keen to try CIGM again, or for the first time, using the very best CIGM products and the help of trained horticultural scientists/growing media professionals who understand both the science and practicalities of using growing media on nurseries. These individuals should work with the growers and the growing media manufacturers during the trials to identify and solve challenges relating to the use of the media (e.g. watering issues, sciarid fly problems, and nutritional difficulties) as they occur. The two WRAP guides (WRAP 2011a and b) provide clear information as to target values for compost parameters and on methods for achieving these values. It is important to ensure that compost producers producing, or interested in producing composts for use in growing media know about these publications and have read and understood them. 3.2.9 Microbiological safety Introduction Under the requirements of PAS100, producers of both green and green/food composts are obliged to run processes that achieve defined thresholds for indicator organisms. Producers of green/food composts (whether accredited to PAS100 or not) are also legally obliged to achieve limits for indicator organisms (under the terms of the Animal By-Products Regulations [ABPR], see Section 3.3.3). This means that the absence of Salmonella must be demonstrated, whilst E. coli (or enterobacteriaceae in the case of ABPR-approved facilities) are permitted below a limit of 1000 colony-forming units per gramme of material tested – which is line with other European approaches to compost quality. The conditions present within PAS100 (and ABPR-compliant) composting processes are sufficient to minimise risks from human pathogens – not only as a result of thermal inactivation but also due to the chemical and microbiological environment during composting (Gale, 2002, WRAP, 2003, 2004b). There have been recent concerns with a specific group of human pathogens, namely Legionella species, and L. longbeachae in particular. This review summarises earlier work to determine recommended sanitisation limits for PAS100 composting processes and more recent developments in relation to the issue of Legionella species in growing media. Previous and current relevant work Much previous work has looked at the effect of (non-PAS100) composting processes on human pathogen numbers, including coliforms and indicator pathogens, in materials other than green waste (for example, sewage sludge or animal manures, which tend to contain much greater numbers of human pathogens prior to composting [WRAP, unpublished]). Physical and chemical conditions in heaps or windrows of composting materials are generally unsuitable for the growth of enteric (gastro-intestinal) bacteria, although growth has been reported in some wastes (Wichuk & McCartney, 2007) including green wastes (Brown et al., 2000; WRAP, 2003). Where such growth occurs, it tends to occur prior to the hottest (thermophilic) phase of the composting process (Brown et al., 2000). In general, sustained temperatures of more than 55oC will kill off most enteric bacteria (WRAP, 2003; Wichuk & McCartney, 2007) and it is likely that this temperature regime should kill off many other pathogens too (Gale, 2002, WRAP, 2003). Studies looking into the presence of microorganisms in growing media were undertaken at Nottingham Trent University from 1995 until (at least) 2008 (Carlile & Hammonds, 2008). Work showed that peat-based media tended to contain fewer coliform bacteria than peat-free media but pathogen numbers were low in both cases and would present a very low risk to human health, especially when compared with coliform numbers considered to present a risk when found in food (Forsythe, 2005). Following extensive literature searching, the


authors of this review could find no reports of people suffering ill effects due to the presence of enteric bacteria in PAS100 composts or in CIGM. Bearing in mind relevant experimental work and the conclusions of the authors considered in this report, the probability of human illness caused by Salmonella species, E. coli. or other enteric bacteria present in composts or CIGM is thought to be very low. Whilst the problem with salmonella and E. coli in CIGM may be perceived (by a limited number of stakeholders) rather than real, the issue with L. longbeachae in composts and CIGM is a real one. However, given the underlying presence of the organism in the wider environment, there are questions about how common the bacterium is in growing media and how serious an issue its presence actually is. Legionnaires’ Disease was originally named after the outbreak in Philadelphia 1976 when a type of pneumonia affected a large number of members of the American Legion, a military veterans association, which held a gathering at a hotel there (De Jong, 2010). Legionella species – the bacterium causing the disease – was identified several months after this outbreak for the first time. Now we know that there are around 50 different species of Legionella and that many are not pathogenic to humans. The great majority of reported cases are a result of infection by L. pneumophila through inhalation of aerosols (water droplets) containing the bacteria. However, some cases are a result of infection by other Legionella species, for example, L. longbeachae, which is well recognised in Australia and New Zealand, and where cases have been epidemiologically associated with the use of growing media (termed ‘potting compost’, Pravinkumar et al., 2010). In a soil survey performed in 1989 to 1990 in Australia, 33 (73%) of 45 ‘potting soil’ (growing media) samples tested positive for Legionella species; 26 (79%) of the 33 contained L. longbeachae (Steele et al., 1990b). For a long time, contamination of growing media by Legionella species bacteria was considered largely to be limited to Australia. For example, Steele et al. (1990a) found that more than two thirds (33 out of 45) of Australian samples and no samples (out of 19 tested) of European growing media tested positive for Legionella species. However, during the past 13 years, associations between Legionnaires’ Disease cases and gardening or use of potting mixes have been reported from a range of countries other than Australia, including New Zealand (Whiley & Bentham, 2011), Japan (Koide et al., 2001), USA (Anon., 2002, cited in Casati et al. (2009a), The Netherlands (den Boer et al., 2007) and more recently the UK (Lindsay et al., 2012). L. longbeachae has only recently been detected as a cause of respiratory illness in the UK. Pravinkumar et al. (2010) and Lindsay et al. (2012) suggested a possible association between handling ‘potting soil’ (growing media) and infection with L. longbeachae in three Scottish cases. Two of these three cases had underlying health problems which were thought to predispose them to infection by L. longbeachae. A more recent Health Protection Scotland report (Health Protection Scotland, 2013) provides a useful overview of the underlying incidences of Legionnaires’ Disease in Scotland, and examines the potential relationship between nine cases of L. longbeachae and gardening activities. It reaches the following conclusions over risk: However, the incidence of L. longbeachae infection in Scotland is very low: less than one confirmed case per million total population per year since 2008 with only one death in a confirmed case in the same period. There is no evidence from Scotland of horticultural workers, who have continuous workplace exposure to compost and growing media, suffering from legionellosis caused by L. longbeachae. Most cases are aged over 55 years of age and most have underlying, chronic diseases. In population terms, the burden of disease (i.e. years of expected life lost, years of life with added disability and years of poor quality of life)


resulting from the infection is comparatively small. Given the volume of growing media products and compost sold and the number of gardeners in Scotland, the risk of exposure to this organism resulting in diagnosed, severe disease appears to be very low. A major difficulty with much of the published research on L. longbeachae is that it rarely states whether or not the organism has been related specifically to one or more ingredients within the tested growing media. In addition, the terms ‘potting soil’, ‘potting mix’, compost and growing media are often used interchangeably, making interpretation tricky. Similar difficulties are encountered in another report from 2013 (Currie et al., 2013), although this clearly states that no Legionella species were isolated from the one sample of PAS100 green compost tested. Further research in this area would be helpful, particularly as there are precedents for (non PAS100) green compost containing Legionella species elsewhere: Hughes & Steele (1994) isolated several Legionella species (including L. longbeachae and L. pneumophila) from six commercial composting facilities (33 samples) and private garden compost heaps (80 samples) in Australia. Casati et al., (2010) isolated six Legionella species (not including L. longbeachae.) from samples of green compost taken during and after composting from compost sites in Switzerland. The question of L. longbeachae is certainly not confined to green composts and CIGM though. It has been detected in other types of growing media including those based on coir, wood fibre, composted bark and more rarely peat (Casati et al., 2009; Whiley & Bentham, 2011). While growing media (including CIGM) are now thought to be a potential source of L. longbeachae bacteria, the exact mechanisms whereby infection takes place are not as yet clear; it may be as a result of aerosols being created during gardening or watering of the growing medium, perhaps most likely in an enclosed space. Other modes, such as ingestion via contaminated hands, have also been postulated (Steele et al., 1990b). It is very important to place in context the risk of human infection from Legionella species bacteria present in CIGM. Evidence shows that it is not specific to CIGM and, in fact, most commonly used types of growing media could potentially contain Legionella species bacteria. Extent to which issue has been resolved The representative of the company interviewed which produced composts for the growing media sector (but did not themselves manufacture growing media) had no problems in achieving the PAS100 limits for indicator pathogens. This company had not been given other, stricter criteria (by their customers) with which to comply and they did not feel that pathogens of relevance to human health were an issue for them, since their customers were happy with their products. The six companies producing both composts and CIGM were divided. Three complied with the PAS100 standards by following the recommended sanitisation criteria in PAS100:2011 (and no additional higher standards), had no problems in doing so and felt that pathogens of relevance to human health were not an issue for them. A fourth had had problems in the past with elevated levels of pathogens of relevance to human health in their composts, but no longer did. That company complied only with the PAS100 standard (i.e. no additional, higher standard) and also felt that pathogens of relevance to human health were no longer an issue for them. The fifth company which complied only with the Dutch RHP standard (the Dutch compost quality accreditation scheme, which has similar limits to those in PAS100:2011) had no problems in achieving the standard, but felt that the issue of pathogens of relevance to human health in composts was one reason why they did not sell more CIGM than they did. The sixth company worked with the PAS100 limits only, but said that they felt that the issue of pathogens of relevance to human health was one reason why they did not sell CIGM into the professional sector at all and sold less CIGM into the retail sector than they might do.


In summary, there was no evidence that any of the companies interviewed as part of this project had trouble reaching the standards for numbers of indicator pathogens in their national compost quality certification scheme (PAS100:2011 for all of the UK companies). Nor was there any evidence that any of the companies were requesting (or aiming for) compliance with a higher standard for human pathogen content. None of the companies mentioned testing for Legionella species either in compost or in CIGM and none said that they had had any problems with incidence of Legionella species in their products. However, despite the above, several growing media manufacturers acknowledged that potential presence of pathogens of relevance to human health was one reason why they did not sell more CIGM. Of the growers interviewed, almost all were concerned about the potential presence of these organisms in CIGM and several cited it as one of the reasons why they did not use it. In summary, the issue of pathogens of relevance to human health in CIGM has been resolved as far as some companies are concerned and they do not cite these organisms as a problem for them. Others feel that the issue has not been resolved, although they did not state whether they were concerned about specific pathogens or pathogens in general. Some questions remain around Legionella, although the growing media sector has recently agreed to standard handling advice on bagged product, following the recommendations of Health Protection Scotland (2013): Health and Safety Advice:

Use in a well-ventilated place and avoid breathing in dust

Always wear gloves when gardening and then wash hands after use

The same report (cited above) suggests that risks from Legionella are very low. Recommendations for minimising the impact of the issue in future Given that there have been no human health questions due to the presence of microorganisms other than Legionella species in CIGM, and that PAS100 composts should contain no Salmonella species and low numbers of E. coli, it can be concluded that the problem (for pathogens other than Legionella species) in CIGM is mainly perceived rather than real (and it is only perceived by some, but not all, of those interviewed). For those who perceive that enteric human pathogens still are a problem, the main challenge will be to improve confidence in CIGM through provision of clear information to stakeholders, rather than to set stricter limits for sanitisation of compost or for numbers of enteric pathogens in compost or CIGM. Given that Legionella species can potentially be present in all types of commonly used growing media, is native to the UK and may be present naturally in soils and on plant material, worries about limiting any impact of the pathogen apply to all growing media (not just CIGM) and potentially to gardeners with compost heaps and workers on compost sites. General (common sense) warnings that users of growing media should wear gloves and wash hands afterwards should certainly remain on all bags of growing media, and compost producers should consider Legionella species in their risk assessments, particularly with regard to bioaerosols. It is important to conduct further research in order to gain a greater understanding of the sources, life cycle and epidemiology of Legionella species (and in particular L. longbeachae). Studies of the incidence and behaviour of Legionella species in green waste during and after the composting process will be particularly valuable. Only then can judgements be made as to how best to minimise the already very small risk to those handling composts and CIGM.


It would also be wise to ensure that those researchers working on Legionella bacteria fully understand the relevant legislation, rules and working practices relating to the manufacture of composts and growing media: some clearly do not. For example, Lindsay et al. (2012) state that there has been a move to “replace peat (in growing media) with green waste” (PAS100 compost is, of course, not a waste). They also state that “Multipurpose Compost (by which they mean multipurpose growing media as defined in this project, although it is often called multipurpose compost in the UK) in the UK is subjected to the PAS100 standard, which involves a sanitisation phase”. In reality, generally only the PAS100 component of growing media will have been sanitised, and many growing media do not contain that component at all. Lindsay et al. (2012) also use the term “compost” without defining it, although they appear to be referring to growing media which may or may not include PAS100 compost. 3.3 Hyperlinked summary of UK legislation and good practice guidance 3.3.1 The UK Compost Certification Scheme and BSI PAS100:2011 The UK Compost Certification Scheme aims to independently certify compost producers who are producing compost according to the BSI PAS100:2011 specification. PAS100:2011 is a baseline quality standard, which ensures that compost is consistent, safe and reliable to use in a range of markets. The UK Compost Certification Scheme is an independently-certified scheme, which is aligned to the requirements of the PAS100:2011 standard. http://www.wrap.org.uk/category/materials-and-products/compost BSI PAS100 specifies the minimum requirements for the process of composting, the selection of input materials, and the quality of composted materials, as well as for the marking and information labelling of the product. In countries, such as the USA, sewage sludge is used in compost, and is largely accepted by the public. In the UK, sewage sludge in not an allowable input under the CQP and is not allowed in PAS 100 compost. Certification involves a series of steps. In January 2013, the Association for Organics Recycling (AfOR) became the Organics Recycling Group (ORG) within the Renewable Energy Association (REA). AfOR’s Compost Certification Scheme and the partnership certification services it provided are now operated by Renewable Energy Assurance Limited, a wholly owned subsidiary of the REA. Advice and assistance on gaining certification can be sought from ORG, the contracted independent certification bodies and approved consultants.

http://www.wrap.org.uk/category/materials-and-products/compost


Further information can be found at the ORG website for more detail. http://www.organics-recycling.org.uk/category.php?category=991&name=Certification 3.3.2 The Quality Protocol for Compost The Compost Quality Protocol (CQP) was launched in England and Wales to provide a clear framework for the production and supply of quality compost; it was updated August 2012. https://www.gov.uk/government/publications/quality-protocol-for-the-production-and-use-of-compost-from-waste The Protocol clarifies the point at which waste regulatory controls on composted source-segregated biodegradable waste are no longer required. The compost producer must demonstrate compliance with the Protocol and approved standard (currently only PAS100:2011 is accepted as a standard). Compliance with the Quality Protocol means that quality compost can be used without the need for waste management controls from the point at which it is dispatched to the customer. The Quality Protocol does not change the regulatory requirements that apply to the manufacture of compost from waste materials. The production and storage of compost can take place only with an environmental permit. 3.3.3 The Animal By-Products Regulations Animal by-products (ABPs) can present a risk to human and animal health if not used or disposed of safely. The type of ABPs used in composting is restricted and the way in which they are processed (in more specialised, contained systems than those permitted for non-ABP materials), is tightly controlled. ABPs are classified into three categories based on their potential risk to animals, the public or to the environment https://www.gov.uk/using-animal-by-products-at-compost-and-biogas-sites . Only the lower risk material (Categories 2 and 3) can be used within an in-vessel composting process. (Categories 2 and 3 cannot be used within open windrow composting). 3.3.4 Guidelines for the specification of Quality Compost used in growing media (2011) In addition to these regulatory requirements for the production of compost used in growing media, WRAP has produced a guidance document to help compost producers who want to supply the horticultural growing media market meet the quality standards required by this sector (WRAP, 2011a, updated 2014). The WRAP guidelines are an update of those

http://www.organics-recycling.org.uk/category.php?category=991&name=Certification

https://www.gov.uk/government/publications/quality-protocol-for-the-production-and-use-of-compost-from-waste

https://www.gov.uk/government/publications/quality-protocol-for-the-production-and-use-of-compost-from-waste

https://www.gov.uk/using-animal-by-products-at-compost-and-biogas-sites

https://www.gov.uk/using-animal-by-products-at-compost-and-biogas-sites


previously published by WRAP in 2004 (Guidelines for the specification of composted green materials used as a growing media component) and are designed to assist producers of composted green materials to better understand and meet the specific requirements for composts to be used in growing media. They are not intended to be prescriptive; the actual detailed specification for compost will need to be agreed with the growing media manufacturer or grower who is purchasing the compost, and will depend on the types of plants to be grown in the mix it is used for. http://www.wrap.org.uk/sites/files/wrap/Growing_Media_Specification.pdf 3.3.5 Compost production for use in growing media – A good practice guide (2011) To help compost producers to use the ‘Guidelines for the specification of Quality Compost in growing media’, WRAP has also produced a ‘Good Practice Guide’ (2011, updated 2014). http://www.wrap.org.uk/sites/files/wrap/Growing_Media_Good_Practice_Guide.pdf The guide covers key areas on feedstock mixes, monitoring and acceptability for inclusion of compost to be used within growing media. It explains process control and screening additional requirements for specific markets such as long term containerised stock or ericaceous media. There is also guidance on testing requirements both broadly for inclusion within growing media, and for specific end uses. Concerns over legionella and herbicide residues are also discussed. 3.3.6 Microbiological safety of pot-grown fresh herbs The use of fresh herbs (loose, pre-packed or grown in a pot) is becoming increasingly popular and is covered by Regulation (EC) No 2073/2005 amended 2007 on the microbiological safety of foodstuffs: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:322:0012:0029:EN:PDF Strategies to prevent fresh vegetables including herbs from being contaminated with microorganisms of concern (e.g. Salmonella spp.) during production are based on control measures taken during production, harvesting and processing. When used as a constituent in growing media for pot production of herbs, the risks of pathogen transfer from the medium itself (rather than just the compost fraction) must be considered. As outlined above, risks from pathogens of relevance to human health are considered acceptably low in PAS100 composts. 3.4 Gap analysis to determine where additional research and development is required Work conducted during this project has led the authors to conclude that several gaps still exist in the knowledge of how to produce top quality composts for use in growing media, and how best to use CIGM in horticultural production systems. However, a general problem is that the few stakeholders who have achieved partial or whole success with one or more of the issues under discussion are unwilling to divulge their findings. With the severe reduction in government funding for horticultural research that has happened over the past 20 years the research is now largely done by commercial companies and, understandably, those who have spent the money achieving success want to keep their valuable knowledge to themselves. The requirements that have, nevertheless, been identified for literature reviews, laboratory work, replicated trials and simple development/demonstration work are summarised below.

Study on the effect of management practices on compost consistency

Some compost producers/growing media manufacturers felt that they had solved the

problem of lack of compost consistency, but many others felt that it had not been

http://www.wrap.org.uk/sites/files/wrap/Growing_Media_Specification.pdf

http://www.wrap.org.uk/sites/files/wrap/Growing_Media_Good_Practice_Guide.pdf

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:322:0012:0029:EN:PDF


solved. It may be possible to find a compost producer (or more than one) who is keen

to improve product consistency and work with them over a period of 12 to 18 months

to implement known best practice in terms of feedstock choice, feedstock management

and process management in order to develop a process which will minimise variation in

compost products. The resulting case study and documented best practice could help

many more compost producers improve the consistency of their products. Provision of

one-to-one technical support for these compost producers may help them improve

their products more quickly and to a greater extent.

Comparison of UK and Dutch composts

It would be useful to compare the properties of RHP-accredited (Dutch) ‘humic

composts’ with the best UK PAS100 composts which are being produced for the

growing media market. UK growers often trust Dutch growers and Dutch compost

products and some view their “humic composts” as superior to composts produced in

the UK. A short project could usefully:

conduct a short literature review comparing the Dutch RHP standard with PAS100; compare existing data (chemical, physical and biological compost parameters) from

Dutch RHP accredited ‘humic composts’ with the best UK PAS100 composts intended for growing media;

compare (if data permit) the consistency of RHP-accredited composts throughout the year and between suppliers and determine whether (and if so why) the RHP composts are superior to UK PAS100 composts;

(where data are lacking) test a range of recent samples of both RHP accredited and PAS100 accredited composts for key parameters (not only parameters which are known to be critical to the performance of composts as components of growing media – e.g. conductivity, stability, pH – but also microbial respiration, the presence of specific microbial species, microbial diversity and other parameters which might make RHP composts superior to UK PAS100 composts in terms of their suitability for use in growing media); and

report on key differences between RHP accredited (‘humic’) and PAS100 accredited composts and determine whether these differences are likely to result in real differences in performance when the two differently accredited composts are used as components of growing media.

Replicated experimental trials at research facilities These should be conducted at research facilities where genuine expertise in growing media and/or container-based crop production exists. In some cases, trials could be conducted on professional nurseries where the grower understands the need for replication and standardisation of management across the trial (other than for the differing treatments). Key challenges needing to be addressed include: Development of methods to reduce salt concentrations in composts (experiments to

test leaching/flooding techniques which do not adversely affect compost properties); Trials to demonstrate that the higher pH values found in CIGM (as opposed to

traditional peat media) do not necessarily cause problems. Some or all of this work could be conducted on professional nurseries, as outlined in the second major bullet point below; and

Development of methods to prevent and control sciarid (and other) flies in both amateur and professional situations. Although some growing media manufacturers felt that this problem had been solved to some extent, several growers disagreed and there is little doubt that some work remains to be done on this subject, Some work should focus on biological control agents, attractants and repellents, but work must


also address the impact of management practices (in particular with regard to irrigation practices) on the incidence and severity of sciarid fly attack. It must be realised that different production systems may require different solutions (e.g. depending on the size of the container, type of irrigation systems available and physical/chemical properties of the growing medium). Some of this work could be conducted on professional nurseries, as outlined in the second major bullet point below.

Validation of composting system sanitisation regime for kill of plant pathogens

of importance Some growing media manufacturers felt that some plant pathogen species may be

able to survive the composting process and that this was a key reason why they chose not to include composts in their growing media. Although plant pathogens were not a key issue under study in this programme, some growing media manufacturers wished to see further work done to show that named plant pathogens of concern were reliably killed under the commonly used time/temperature/turning regimes commonly used in UK PAS100 composting systems.

Nursery-based comparison trials and demonstration of best practice on

professional nurseries These are needed in light of the general issue of ownership of research and the need

to demonstrate and disseminate good practice for use of CIGM. Ideally this should follow completion of essential work in the previous major bullet point. Simple trials should be conducted on the nurseries of growers who are genuinely keen to try CIGM again, or for the first time, using the very best CIGM products and the help of trained horticultural scientists/growing media professionals who understand both the science and practicalities of using growing media on nurseries. These individuals should work with the growers and the growing media manufacturers during the trials to identify and solve challenges relating to the use of the media in ways which are appropriate to the growing systems in place (e.g. watering issues, sciarid fly problems, nutritional difficulties) as they occur;

The main aim would be to demonstrate the benefits of compost, such as nutrient supply and chemical buffering (e.g. it would be useful to prove that growers can use a lower rate of controlled release fertiliser if compost is used in the growing medium and hence money can be saved during the production of longer term crops like nursery stock); and

Choice of participating grower(s) would be key to the success of this work, since the growers chosen must be prepared to share the results widely.

Studies on disease suppression Several growers said that if certain composts or CIGM could be shown to suppress

disease then they would be interested in trying these products again, since the number of pesticides available to professional growers continues to diminish year on year and there is a pressing need to develop effective alternative disease prevention and control strategies. There is clear evidence that composts and CIGM can suppress disease in container-grown crops: both are widely used in the USA for this purpose, but are not currently used in the same way in the UK. Whilst compost teas have become popular on many ornamental plant nurseries in both the UK and Holland and many growers believe that they help to suppress disease, very little work has been done to develop disease suppressive composts for use in ornamental UK container production systems. Detailed work is required to identify the characteristics of disease suppressive composts and to develop methods for producing reliable and consistent products.


Sampling and laboratory testing - further study on Legionella species bacteria The GMA considers (probably correctly) that Legionella species pose an extremely

low risk and are therefore best not mentioned at all on bags of growing media. However, we do not really know for sure whether PAS100 composts contain Legionella species, whether they can survive and proliferate in CIGM and whether they can then go on to cause infection and disease. Further information will almost certainly be called for if further outbreaks of Legionnaires’ disease are associated with growing media. In that case, independent research will be required to gain a greater understanding of the sources, life cycle and epidemiology of Legionella species (and in particular L. longbeachae). Studies of the incidence and behaviour of Legionella species in green waste and during and after the composting process will be particularly valuable. Only if further scientific work is done can judgements be made as to how best to minimise the already very small risk to those handling composts and CIGM.

3.5 Proposal for knowledge exchange (KE) mechanisms It became clear when working on this project that many of the issues under study have been resolved, at least in the minds of some stakeholders. Effective knowledge exchange is vital in order that mechanisms for minimising the impact of the issues under study are disseminated and fully understood. Knowledge exchange mechanisms are therefore proposed as follows.

Development of new or revised template documents, information pamphlets

and guidance Review the ORG templates on minimising physical contamination in feedstocks and

composts to ensure that they cover all relevant points; Develop a simple, detailed guide for local authorities, waste handlers/suppliers and

compost producers on why contamination in feedstocks and composts must be minimised and how to achieve composts which are consistently free from contamination. The guide could be produced in the traditional leaflet/pdf file but also as a more interactive, simplified, web-based decision tree. A short video clip of a leading gardener who is pro green compost inclusion could also be produced, but showing the technical aspects of the composting process;

Review good practice guidance (WRAP 2011a and b) to ensure that the latest and best information is included on the issues discussed in this report;

Produce a user-friendly, practical grower fact-sheet on using compost in ‘own mix’ or ready-mixed professional growing media (similar to other WRAP fact-sheets). Several of these could be produced following completion of grower trials on different plant types. They would include information on sourcing the best quality compost, reference the WRAP guides for specifying compost, and detail what to ask for; and

Improve the labelling and product information on growing media bags and product information/dispatch sheets. There is still a widespread lack of understanding of the difference between a growing medium (often labelled compost in the UK) and PAS100 compost (which will never on its own make a suitable growing medium for young plants). This is without doubt the reason behind some amateur and professional growers’ mistrust of PAS100 composts.

Promotion of new and existing information relevant to increasing the use of

quality composts in growing media Promotion of relevant (new and old) templates and guidance aimed at solving the

challenges (real and perceived) which high value compost producers and growing media manufacturers have in relation to the use of composts in growing media: Topical, colourful, easy-to-read, short trade press articles (production horticulture,

garden centre/retail) drawing attention to relevant (new and old) templates and


guidance aimed at high value compost producers and growing media manufacturers;

Targeted emails to compost producers’ known to (or likely to) want to reduce contamination in their products. Aim: to draw attention to the latest ORG recommended procedures and rules for reducing contamination in feedstocks and to recent new and revised publications on how to optimise compost properties in composts intended for use in growing media; and

Trade stands at key shows including Four Oaks (http://www.fouroaks-tradeshow.com/) and the IPPS conference (http://www.ipps.org.uk/).

Improve confidence in CIGM through provision of clear information to stakeholders (particularly growing media manufacturers and growers): on the safety of current PAS100 composts (rather than to set stricter limits for

sanitisation of compost or for numbers of enteric pathogens in compost or CIGM); by drawing attention to the latest ORG recommended procedures and rules for

reducing contamination in feedstocks and to recent new and revised publications on how to optimise compost properties in composts intended for use in growing media;

by drawing attention to future project reports/case studies where compost producers had greatly improved their products through careful management regimes or where compost products had been used successfully on professional nurseries;

by ensuring that researchers working on Legionella species bacteria fully understand the relevant legislation, rules and working practices relating to the manufacture of composts and growing media. This will require a short study to determine who is working on the issue, followed by a simple targeted letter explaining the facts.

Two key methods are suggested for the above confidence-building: A telephone/e-mail ‘campaign’, which could be launched with an invitation to

come and discuss issues in an open forum, with three technical experts providing talks on the main issues of concern.

Provision of an internet discussion forum (for use only by invitees). In Year 1, the title page could provide links to important technical information. Individuals would be able to post questions to at least three technical experts who will provide evidence-based answers to discussion points. In Year 2, the knowledge exchange could be summarised from the discussion traffic to produce improved answers and technical information.

Tailor-made training courses/presentations based on existing information Provision of training courses on production of high value composts for use in growing

media. Courses should be tailored to the target audience and could use video clips, online training or in-house training as vehicles to get the message across. The training could be built into existing training platforms rather than be stand-alone. BASIS (registration) Ltd are working with the Horticultural Trades Association

(www.the-hta.org.uk/) and have a dedicated training Continual Professional Development (CPD) registered course for garden centre staff called ‘Guardian’. This is largely pesticide use information. They plan to migrate this short course to a web-based training module with a multi-choice questionnaire. A member of this project team discussed with BASIS whether they would be happy in principal to host a similar style training module on CIGM. BASIS are very amenable to progressing this. Garden centre staff are often very negative about reduced peat and peat-based media (including CIGM). If they better understood the advantages and disadvantages of using CIGM and knew how best to use them, they may be more likely to sell them with enthusiasm;

http://www.fouroaks-tradeshow.com/

http://www.fouroaks-tradeshow.com/

http://www.ipps.org.uk/

http://www.the-hta.org.uk/


Producers: Courses should explain how producers can overcome all of the major issues, with reference to the most recent and best information and guidance. Training should concentrate on how to overcome the genuine issues associated with production of composts for growing media (e.g. physical contamination, bulk density, consistency of composts), but other (to a large extent perceived) issues which remain a concern for some compost producers, growing media manufacturers and retailers should also be discussed;

Growing Media Manufacturers: Development and delivery of a dedicated seminar or slot within a seminar for growing media manufacturers on the key chemical, physical and biological aspects of using composts in growing media. It is acknowledged that some may be reluctant to take part for reasons of commercial confidentiality; and

Commercial Growers: Development and delivery of a dedicated seminar for growers wishing to use CIGM. This course should be developed and delivered following completion of the simple development work and nursery-based trials outlined in Section 3.4 and would cover solutions to the main questions/issues which growers currently have relating to the use of CIGM, including all nine of those addressed in this project. These training courses may be localised but could also be filmed in a series of short clips to make them more accessible to a wider audience.

Demonstration days/grower walks Grower walks/demonstration days should be organised either as standalone, short

events, or in association with dedicated events (for example in association with existing trade shows or conferences/seminars of membership organisations such as the International Plant Propagators Society) in order to explain how to overcome the major issues associated with using CIGM in theory and in practice;

Grower advocate days could be hosted at RHS sites around the country as they have good geographical distribution (Yorkshire, Essex, Surrey, and Devon) and have excellent facilities. These events would be similar to the “Farmer to Farmer” events currently being organised by WRAP. Speakers might include growing media technical experts and/or senior gardeners from the Royal Horticultural Society (RHS), who could be trained up to spread the message. Well-respected horticulturists/growing media specialists must be used for this work and it is likely that their ability as both speakers and advocates will be critical to success;

The Horticultural Trades Association (HTA) National Plant Show - This takes place annually in June in the Midlands. It showcases the very best of British plant suppliers all under one roof and would therefore be a good opportunity for producers of CIGM to reach nursery stock growers (and potential users of CIGM); and

Engagement with key partnership organisations such as the RHS, the National Trust or The HTA should be considered. For example: our survey indicated that the RHS were in favour of the use of CIGM and they may be prepared to run events for growing media retailers and/or gardeners to publicise their views and methods for using CIGM in practice. Both the RHS and the National Trust already run programmes of events and talks and may be prepared to consider running events on the subject of CIGM.


4.0 Conclusions and recommendations 4.1 General points Nine issues of concern have been addressed in this project: physical contamination, high bulk density, high pH, high electrical conductivity, weed seeds, sciarid flies and other pests, compost shelf life, compost variability and the presence of human pathogens.

A review of relevant literature including peer-reviewed papers, conference papers and

current legislation and guidance documentation showed that a significant amount of

(mainly UK) work has been done in efforts to solve these nine issues. In most cases,

evidence from the literature suggested that it was possible to minimise the impact of

these issues in composts and compost-included growing media (CIGM) to levels which

were likely to be acceptable, at least for some stakeholders.

However, in two instances, further research may be warranted. In the case of sciarid

flies, available evidence suggested that further scientific work was required in order to

address the issue effectively (for users of growing media). Further work may also be

required in future to determine the frequency and typical distribution of Legionella species

in PAS100 composts and CIGM.

A range of twenty eight stakeholders were interviewed as part of this project, in an effort

to determine the extent to which the nine issues of concern represented problems for

them in terms of their sales or use of growing media. A broad range of views was

obtained (and listed in Appendix 1) and it was clear that there were strongly opposing

views on whether each issue remained a barrier to sale/use.

Seven compost producers (of whom six also produced growing media) and an additional three growing media manufacturers participated in the study. Their views differed greatly, with some feeling that most of the nine issues had been effectively solved, and others feeling that none of them had! Most stakeholders had some remaining concerns, and most often, those included the presence of physical contaminants, high compost bulk density and high compost EC.

Of the eight growers interviewed, two used CIGM to some extent, two did not know whether their growing media contained composts, and the remaining four did not currently use CIGM. The survey clearly showed that physical contamination and lack of consistency in the product were the major barriers to growers using growing media containing PAS100 compost. Five out of eight growers listed physical contamination as a major barrier, and six out of eight cited lack of consistency. However, nearly all of the factors listed were deemed a barrier to use for one or more of the growers interviewed. It is fair to say that the views of some respondents were based on preconceived ideas rather than on actual experiences of using CIGM.

Six growing media retailers were contacted, but only two replied. Of these, one sold CIGM and one did not, due to concerns over all nine of the issues under study in this project. The retailer who did sell CIGM felt that physical contamination, high bulk density, sciarid flies, shelf life/consistency of product, and poor customer perception limited sales.

The great majority of the compost produced in the UK is made for and sold into the

agricultural market, which is considerably less demanding than the growing media

market. It is important to note that much of the bad press which composts have received

in relation to their potential for use as growing media constituents and many of the poor

reports from growers and growing media manufacturers relates to non-PAS100 composts

or PAS100 composts produced for the agricultural market, rather than those produced


specifically for higher value markets according to higher standards (such as those

recommended in the WRAP Guidelines for the specification of quality compost for use in

growing media, WRAP, 2011a). It is therefore vitally important to inform growing media

manufacturers, growers and retailers of growing media of the great strides which have

been made in recent years in improving compost quality and consistency through

effective knowledge exchange, in addition to conducting relevant research and

development. The most important knowledge exchange, research/development and

demonstration requirements for each of the major stakeholder groups in the context of

the subject of this report are summarised below.

The extent to which the nine issues of concern have been solved for stakeholders in the

growing media sector and the further work and knowledge exchange required (based on

both a study of relevant literature and stakeholder opinions) are summarised in Table 7

and in the following sections.

4.2 Compost producers It is clear that some compost producers felt that they have solved the nine key

issues addressed in this project through hard work, attention to detail and investment in their systems and processes, whereas others still have concerns about some or all of them, particularly physical contaminants and high compost bulk density.

The most pressing need for compost producers in relation to the issues raised in this project is for effective guidance documentation, effective distribution and promotion of this guidance documentation and appropriate knowledge transfer. These are outlined in more detail in Section 3.5.

Compost producers would also benefit from publications released following completion of recommended research and development outlined in Section 3.4.

Most compost producers will continue to prefer to produce composts for less demanding

markets (e.g. agriculture) or may be forced to do so due to inappropriate feedstock

quality or a lack of growing media manufacturers local to them. However, some are well

placed (both geographically and in terms of their composting systems) to supply high

quality products for growing media manufacture. Dialogue should be encouraged between

growing media manufacturers and compost producers new to that sector or considering

involvement in it, with a view to setting up new working relationships between the two

groups. It is important that compost producers understand that additional investment in

procedures and infrastructure is likely in order to satisfy the demands of this sector.

However, it is also important for the growing media manufacturers to understand that

compost producers must be paid a viable price for an improved product;


Table 7 The extent to which the nine issues of concern have been solved for stakeholders in the growing media sector and whether further work and knowledge exchange is required for each issue.

Does literature suggest that:

No. of stakeholders (out of the total contacted) who felt that issue has been resolved (though it

still may limit % inclusion of compost in growing media or sales of compost or growing

media)1

Stakeholder opinions

Issue partial or complete solutions

exist?

further R&D

required?

Compost producers and growing media manufacturers

Growers Retail Further R&D

required?2

KE required

?3

Physical contamination

Yes

no

8/11

2/8

2/2

no

yes

High BD Yes no 8/11 4/8 2/2 no yes

High pH Yes no 8/11 5/8 1/2 yes yes

High EC Yes no 8/11 3/8 1/2 yes yes

Weed seeds Yes no 7/11 4/8 1/2 no yes

Sciarids etc. Yes yes 8/11 5/8 2/2 yes yes

Shelf life Yes no 8/11 6/8 2/2 no yes

Consistency Yes yes 7/11 0/8 2/2 yes yes

Human pathogens Yes possibly 7/11 5/8 1/2 possibly yes 1NB: Ten compost producers and growing media manufacturers, eight growers and two retailers provided their views during the stakeholder interviews. 2For details, see Section 3.4 (or summary of gap analysis above) 3For details, see Section 3.5 (or summary of priorities for knowledge exchange below)


Compost producers interested in supplying composts for use in growing media could

benefit greatly from forming a group or co-operative, in order to share knowledge and

promote their products in a cohesive way to potential buyers;

ORG has expressed a strong interest in providing certification (for PAS100 compost

producers through REAL) to a higher specification for composts intended for growing

media. A standard equivalent to PAS100 would be prohibitively expensive to run.

However, it would be possible to certify PAS 100 accredited producers to additional

criteria such as those set out in a specification such as the WRAP one (WRAP, 2011a).

Compost producers interested in supplying composts for use in growing media could

benefit significantly from such a scheme. If there is sufficient demand, REAL could

extend the scope of the compost certification scheme to include assessment for

conformance with the WRAP specification for compost use in growing media. On

composters’ request and at an additional fee, REAL’s certification bodies could check

compliance with the WRAP specification for compost use in growing media in addition to

PAS 100 and the Compost Quality Protocol. This will only be possible if REAL’s

Certification Bodies agree to provide this service; and

Compost producers must be prepared to develop a close working relationship with the

growing media manufacturer(s) to which they supply. Only by working closely together

can both parties develop a profitable, successful partnership.

4.3 Growing media manufacturers

It is clear that some growing media manufacturers felt that they have solved the nine key

issues addressed in this project, whereas others still have concerns (in some cases serious

concerns) about some or all of them, particularly physical contaminants, high compost

bulk density and lack of consistency amongst composts and produce no CIGM or limited

amounts of CIGM as a result.

There is a clear need to ensure that growing media manufacturers understand the great improvements in compost quality which have been made in recent years. Many of them have considered using or have used composts in the past which were not even PAS100-accredited, let alone produced according to a modern, higher specification such as that produced by WRAP (2011a). Some leading industry players have formed very poor opinions of composts which are evidently deeply ingrained.

Growing media manufacturers would benefit from publications released following completion of recommended research and development outlined in Section 3.4.

It may be possible to improve the understanding which growing media manufacturers have about composts as constituents of growing media through improvement of and promotion of the latest guidance documentation as outlined in Section 3.5.

4.4 Growers

Most of the growers contacted in this study had serious reservations about the use of

CIGM and most had a poor understanding of its characteristics and how to use it to best

effect in their cropping systems. Some of the growers have used (or have heard about

colleagues using) CIGM in the past which was of poor quality. There products were

unlikely to have been based on PAS100 composts, let alone on composts produced

according to a modern, higher specification such as that produced by WRAP (2011a).

However, some leading growers have formed very poor opinions of CIGM, which are

evidently deeply ingrained.

Nursery stock growers are the most relevant target grower group, since the crops they

grow tend to be less sensitive than those produced in other sectors (e.g. pot herbs,


bedding plants and vegetable transplants). Nursery stock growers could provide a

significant market for CIGM and are worth working with in order to increase use of CIGM

in professional horticulture.

There is a clear need to ensure that growers understand the great improvements in the quality of CIGM which have been made in recent years, though that may be difficult to achieve. Some of the reservations which growers have over the use of CIGM for some of the more sensitive ornamental crops may be justified.

Limited research and development work (including work to look at potential benefits of using CIGM) and considerable efforts in relation to demonstration and knowledge exchange are recommended if UK nursery stock growers are to comprehend the recent improvements in CIGM and consider using them in their production systems. Recommended research, development, demonstration and knowledge exchange mechanisms are outlined in Sections 3.4 and 3.5.

4.5 Retailers of growing media

Only two of the six retailers contacted took part in the project, therefore it is difficult to

provide a balanced view of what UK retailers feel in general. The views of the two

retailers who did take part differed greatly, with one cautiously positive about the use of

composts in growing media and sales of CIGM and the other whose company was not

prepared to sell CIGM at present due to concerns about its quality, consistency and

safety.

There is a clear need to ensure that retailers of growing media understand the great

improvements in the quality of CIGM which have been made in recent years, though

that may be difficult to achieve before the recommended research, development,

demonstration and knowledge exchange have been undertaken;

Reports from the recommended research, development and demonstration activities

set out in Section 3.4 may encourage retailers of growing media to increase their

purchase of CIGM;

Updating, publication, distribution and promotion of guidance documentation and

appropriate knowledge transfer as outlined in Section 3.5 will also help retailers realise

the potential for CIGM sales; and

Challenges remain, but if the above recommendations are implemented there should

be greater success with CIGM.


5.0 References AHDB: HDC (2013) Tracking Peat usage in Growing Media Production. Grower Summary CP100

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Appendix 1- Interviews of selected

industry stakeholders

A.1.1 BSI PAS100 compost producers and growing media manufacturers Seven compost producers (of whom six also produced growing media) and an additional three growing media manufacturers participated in the study. All of them supply to the UK market and one of them is based in Germany. They are either PAS100 compost producers who supply to the growing media industry or use PAS100 compost within their growing media mixes or are both a PAS100 compost producer and a growing media manufacturer using their own composts in their growing media production. The exception is the German company, which produces composts to the Dutch RHP specification and is a major supplier of growing media to the UK professional grower market. (It does not use UK PAS100 composts in its media). The Environment Agency accepts that imported waste derived compost may cease to be waste provided it has been produced in compliance with:

a relevant standard or code of practice of a national standards body or equivalent body of

any European Economic Area (EEA) State; or

any relevant international standard recognised for use in any EEA State; or

any relevant technical regulation with mandatory or de facto mandatory application for

marketing or use in any EEA State.

These must give levels of product performance and protection of human health and the environment, equivalent to those required by the Compost Quality Protocol. All respondents who expressed an opinion felt that their sector was undergoing expansion and provided valuable insights into their views on the questions posed; though almost all preferred not to have their views directly attributed to them. Factors which affect the sales/use of PAS100 compost in growing media production The ten compost producers and growing media manufacturers who took part in the project were asked to indicate the extent to which the nine issues considered affected their sales or their use of PAS100 compost in growing media. Responses were rated in terms of the extent to which each issue remained a problem for the interviewees and these responses have been summarised in Figure A.1.1


Figure A.1.1 The extent to which compost properties affect sales and use of PAS100 compost in growing media

A broad range of views was obtained and it was clear that there were strongly opposing views on whether each issue remained a barrier to sale/use. Some growing media manufacturers/compost producers felt that they had resolved most of the issues of concern, whereas others felt that most of the issues listed above remained a problem for them. The issues of greatest concern included physical contamination, high bulk density, high EC and customer requirements which preclude or limit the use of green compost. Some of those interviewed also felt that fungi and pesticide residues were potential barriers to the use of PAS100 compost in growing media. The markets for the growing media produced have differing sensitivities. Professional growing media is the most demanding market, followed by retail growing media, whereas the use of PAS100 compost for inclusion within landscaping projects is, broadly speaking, deemed the least demanding market. Extent to which issues are perceived to have been resolved Opinions as to whether the issues of concern had been resolved varied amongst stakeholders. One compost producer and growing media manufacturer felt that they had put a number of measures in place throughout the compost production process to resolve the issues of concern, but would like to see:

removal of aminopyralid & clopyralid from the supply chain, starting with the removal of

retail approvals for clopyralid;

improvement in understanding of best practice with regard to contaminant removal and

screening techniques at compost sites; and


more compost producers keeping maturing and finished composts dry and ready for

effective screening.

Others felt that the perceived issues were unlikely to be overcome. Perception of potential benefits from inclusion of PAS100 compost in growing media The nine respondents were also asked to review a list of potential benefits of including PAS100 compost within growing media and to rate their responses from the following choices: agree, disagree, neither agree nor disagree. Figure A.1.2 shows the results compiled from these responses.

Figure A.1.2 Stakeholder opinions on the potential benefits of PAS100 compost inclusion within growing media mixes

Range of values sought for key parameters The characteristics of PAS100 compost can vary between suppliers and a stakeholder’s perception of PAS100 compost might be affected by the particular supplier they use or have encountered in the past. We were therefore keen to identify the range of values our stakeholders expect from PAS100 compost that they would consider to be suitable for use in growing media. Seven of the stakeholders replied to this question in detail (five produced both compost and growing media and two produced only growing media). The responses are provided in Table A.1.1.


The BSI PAS100:2011 limits relevant to this project are:

Physical contamination:

total glass, metal, plastic and any other non-stone fragments > 2 mm must not be

present at more than 0.25% (mass/mass) of ‘air-dry’ sample.

plastics must make up not more than 0.12% (mass/mass) of ‘air-dry’ sample.

stones > 4 mm must make up not more than 8% (mass/mass) of ‘air-dry’ sample in

compost grades other than mulches.

Weed propagules must not be present in 1 litre of compost;

Salmonella species must be absent and E. coli numbers must be ≤1000 cfu/g fresh

compost.


Table A.1.1 Stakeholder (S) specifications for parameters of concern

Parameter Units S 1 S 2 S 3 S 4 S 5 S 6 S 7


% m/m expect lower than PAS100 specification.

< 10 mm. No sharps.

PAS100 for stones and plastic. Glass trace specified by

internal method 0.1 piece /litre max. Zero preferred

zero nil (further screening is carried

out prior to inclusion in growing

media) <8 mm screen but still get occasional glass contamination

zero (RHP norm) low but not too low to achieve

<0.01

pH pH Units 7 – 8 7 - 9 <7.5 <8.0 <8.0 <7.0

High bulk density

g/l hope to get 450 g/l max

450 - 550 <500 g/l fresh

<550 <700 <500 <500

Electrical conductivity

EC µS/cm <1000 µS/cm <1000 (Target 600)

<1500 <2500 <1200 <1500

Weed seeds % 0 0 (Fungal spores

more of a problem than weeds)

0 0 0 (RHP norm) 0 0

Sciarid flies and other pests

Present/ absent

absent ideally absent absent absent absent absent absent

Compost shelf life

Months almost indefinite 6 Stable (RHP norm) 12 12

Consistent product?

yes/no No (not deemed necessary)

yes (Solvita used)

yes yes yes yes always

Microbiological safety

no. of CFU/ml

No 1000 PAS100 limits Salmonella & Camphylobacter

species nil E.coli <1000

Enterobacteriaceae <10,000

<1,000 None (?)

Other (if named

above)

Odour low – an

earthy rather than putrid smell. No

smell of ammonia

particle size <10mm nitrate >50 mg/l

NH4 to NO3 ratio (no ratio given)

NB: where boxes have been left blank, the stakeholder did not provide a response for the parameter in question.


It is clear from the compost producers’ answers that the expectation is for a lower physical contamination level in compost destined for inclusion within growing media than that required by the PAS100 standard, with zero or nil often stated as a requirement. The microbiological safety levels for indicator pathogens (E. coli and salmonella) seem adequate within PAS100 and match user expectations, as does the weed seed limit of 0%. One growing media manufacturer’s representative indicated in some detail whether he felt it was achievable to source compost which would meet market needs for all nine parameters of concern. This representative has a thorough knowledge of the physical, chemical and biological properties of composts and a comprehensive understanding of the needs which plants have with regard to growing media. He is well-respected within the growing media sector, is arguably one of the most technically able practitioners in the field and his views are thought to represent those of the industry as a whole. His views are summarised in Table A.1.2.

Table A.1.2 Comments of one stakeholder about the potential for sourcing compost for use in growing media which satisfied the requirements for parameters of concern

Parameter Comments on the growing media manufacturer’s ability to source compost with appropriate value for the parameter

Physical contamination Whatever the limits set, it only takes one object, e.g. a biro top or bottle top, to convince the consumer that they have purchased rubbish.

pH Always high, impossible to reduce.

High bulk density Inevitably high, an issue because of the carbon footprint.

High electrical conductivity Not just high EC, but certain salts such as chloride.

Weed seeds Very few samples reach specification and it is evident from trials with competitor products that this is an issue.

Sciarid flies and other pests If not already present they will “join the party”.

Compost shelf life This is not defined in PAS100a; most manufacturers will be looking for 6-12 months storage stability. The WRAP storage trial showed poor results with growing media containing green compost that did not contain a high percentage of peat.

Consistent product? There is no consistency in PAS100 composts; this is inevitable, given the material used.

Microbiological safety An area of great concern when supplying food retailers. aShelf life is not defined in either the PAS100 standard or in the WRAP specifications or guidance (WRAP 2011a and b). Shelf life would depend on the conditions under which compost is stored, therefore if composts are to be compared and/or the shelf-life defined for specific products, the storage conditions under which they were to be kept would also have to be defined.

This producer felt strongly that very few suppliers can currently achieve the necessary high standards in order to supply large manufacturers. He didn’t dismiss the possibility of using compost in the future, but at present the PAS100 compost on offer is in small quantities, of mediocre quality and variable consistency, which requires excessive quality control procedures on each batch. Discussion points on using PAS100 compost in growing media Finally, discussion points were raised by the PAS100 compost producers and growing media manufacturers. These have been summarised below:


Should standards for production have been focused on the end product (market

requirements) rather than the requirements of organics recyclers?

Has the BSI PAS100 standard encouraged the government and other bodies to have too

much faith in the ability of green compost to fill the gap in the market caused by the need

to stop using peat?

Recent publicity relating to the presence of herbicides in composts has not helped the

case for using green compost in growing media. If anything, this publicity has

strengthened opposition from the professional growing sector.

Is there enough green compost of sufficient quality to justify the use of such material in

UK growing media and would effective quality control measures render their use non-

cost-effective?

Current growing media production has complete traceability and is supplied to high

auditing standards. Could this be achieved with compost-included growing media?

The Defra SGMTF determined that reduced peat and peat-free growing media must be “fit

for purpose” if consumers were to be convinced of their usefulness. However, tests

conducted by some growing media manufacturers showed that compost-included growing

media was not fit for their purposes.

Asked what would be required to encourage further inclusion of PAS100 compost in growing media, the following comments and suggestions were raised from several stakeholders:

Reduction of soluble salts, particularly Na, K, Cl, in the compost media;

Reduction of contamination, particularly glass contamination, to virtually zero;

Consistency in the output of [each] composting site and less variation between sites;

Improved control on particle size;

Publicly available growing trial data is useful but of more use would be to get the basics

right;

Guidelines are of no use and should be changed to requirements;

Compost bulk density should be lower;

Trials carried out through the new Growing Media Panel. Work should be conducted

according to the new trial protocols, developed by this group, firstly to prove that BSI PAS

100 composts can be part of growing media that are fit for purpose and secondly that

there will be a sustainable source of sufficient quantity of this material available; and

Education, since management of compost-included growing media is different to peat-

based, and users (whether amateur or professional) need to understand how to use it in

order to gain from their advantages and minimise their disadvantages.

A.1.2 Growers who may use growing media containing PAS100 compost Eight leading growers were interviewed to gain their views on using growing media containing PAS100 compost. All of the growers interviewed obtained growing media from named manufacturers, which they then used ‘straight’ or mixed with additional materials on site. Factors which might affect the use of growing media containing PAS100 compost Growers were asked to indicate the extent to which the nine issues considered in this project affected whether they would use growing media containing PAS100 compost growing media. Their responses are summarised in Figure A.1.3. The results of the survey clearly showed that physical contamination and lack of consistency in the product are the major barriers to growers using growing media containing PAS100 compost.


Extent to which issues are perceived to have been resolved Responses varied considerably. One grower said that his supplier currently does not offer growing media based on composts and that in any case, they did not want it. He felt that PAS100 standards are not stringent enough for growing media for commercial production and to some extent are questionable even for amateurs. Other growers said they would consider the inclusion of compost in their growing media if quality could be improved, if there was a guarantee of sufficient supply and if it did not entail additional cost. Another grower commented that they were currently using a medium which included 10-20% compost by volume. They went on to comment that the compost-included mixes were useful to them.

Figure A.1.3. The extent to which listed factors affect whether growers use growing media which contains PAS100 compost.

Perceived benefits of including PAS100 compost within growing media The growers were also asked whether they agreed, disagreed or neither agreed nor disagreed with a list of potential benefits to including PAS100 compost in growing media. Their responses are summarised in Figure A.1.4. Range of values expected within the growing media used All growers were asked to list the range of values required for key parameters in the growing media they use. Seven out of eight growers provided these details, with the eighth grower relying on the technical knowledge of his supplier to provide the correct characteristics. The information is provided in Table A.1.3 below. Discussion points on using growing media containing PAS100 compost In summary, of the eight growers (from nine nurseries) interviewed, two used growing media containing PAS100 composts (although one used only a very small amount in large containers). Two growers did not know whether their growing media contained composts or


not, and the remaining four clearly stated that the growing media they used did not contain PAS100 compost. To encourage them to use compost within their growing media, reassurances on compost traceability, safety, consistent quality, lack of physical contaminants and acceptable price are needed. Good technical trials were also requested.

Figure A.1.4. Benefits (perceived by growers) when PAS100 compost is included in growing media


Table A.1.3 Characteristics required in growing media (as recorded from grower responses to survey)

Characteristic Units Grower 1 Grower 2 Grower 3 Grower 4 Grower 5 Grower 6 Grower 7


% m/m

0

0

Nil

Nil

0

negligible

pH pH Units 5-6.25 (depending on mix)

5.8 5.0-6.0 3.0-5.0 5.5-6.5 5.0-6.5

High bulk density

g/l 250-500 200-300 low 500

High electrical conductivity

EC µS/cm or mS/cm

<550 0.5-1 low <1000 0.7

Weed seeds % 0 nil nil 0 nil 0


Present/absent Absent absent nil absent absent Accepted but needs control

absent

Compost shelf life

Months 12 (without controlled release fertiliser)

1 3 Medium lifetime 3

Consistent product?

Yes/No Yes Yes

Yes Yes yes yes Yes


no. of CFU/ml 0 Number of standards to follow

Must be safe Safe as possible, staff use latex gloves for potting

?


A.1.3 Retailers’ perception Two major retailers responded to a survey designed to find out their views on the inclusion of PAS100 compost within growing media. The first has a significant share of the UK retail market, selling to mainly amateur gardeners. PAS100 compost is included within a wide range of growing media products blended to meet specific plant needs, at an inclusion rate of 25-90%. This retailer said that although they used PAS100 certified compost in their growing media they are still seeing too many problems with it. He felt that physical contamination, high bulk density, sciarid flies and pests, shelf life and consistency of product, and poor customer perception all limit their sales of growing media containing PAS100 compost. He also said that compost pH, high electrical conductivity, weed seeds and microbiological safety have never been an issue for them. He felt that in order to encourage further use, good price, public pressure and excellent trial results would all help with both the internal decision-making processes and eventual sales. The second retailer sells to amateur gardeners within the UK and the Republic of Ireland. Whilst their representative agreed with all the potential benefits of PAS100 compost inclusion within growing media mixes, he felt that all of the factors listed prevented them from selling such a product. He stated that they had ticked all of the issues in section 3 (of the questionnaire) as factors of concern if they were to use PAS100 compost in their own brand compost. He felt that all of the issues would need to be considered as they would with any other type of growing media sold, along with the product performance. He did understand that PAS100 production systems give an element of control over the concerns raised, but he felt that they still need to be further addressed. He said that good growing trial results and consistency of products were key factors for his company when looking at alternative growing media, and that through years of their own trials, they were simply not seeing the required quality coming through. He said that customer perception remained a concern to his company, and he felt that customers would not be able to manage such media, since they behave differently to peat and coir-based media. Another major concern was the relatively heavy weight of growing media based partly on composts, which is especially important when selling in retail bags.


Appendix 2 - Questionnaires used

A) Questionnaire on the use of BSI PAS 100 Compost in growing media for PAS 100 compost producers and growing media manufacturers

WRAP (Waste and Resources Action Programme) has commissioned a short project (Project OMK005-002) which is looking at the use of PAS 100 composts in growing media. The purpose of the work is to improve awareness in the use of composts within the growing media industry by collating and/or signposting existing information on its safe, effective use and by identifying the nature of further research action, if this is required. The work is also intended to support an increase in the use of compost as a constituent of growing media. A number of questions around compost use in growing media have arisen within the Defra Sustainable Growing Media Taskforce (SGMTF). These concern issues including physical contamination, pH, bulk density, electrical conductivity, weed seeds, sciarid flies, compost shelf life, compost consistency and microbiological safety. In addition to a short literature review, Project OMK005-002 aims to gather information through a survey of key players in the composting, growing media manufacturing, retailing and growing sectors. Each industry stakeholder interviewed will be asked questions relating to their involvement in the composting and/or growing media sector, with particular reference to their attitudes and experiences with the above issues. The results of the survey will be collated and summarised in a report which will aim to help improve the quality of both composts and growing media which contain composts (as required under the SGMTF roadmap). Availability of PAS 100 quality composts has increased in recent years as a result of government targets for landfill diversion and recycling and due to increasing pressure to reduce use of peat in their products, many growing media manufacturers use PAS 100 composts as a constituent of one or more of their products at varying inclusion rates. Although most growing media manufacturers use green composts (which have been made purely from source-segregated garden wastes) in their products, this project concerns both green composts and food/green composts which also include food wastes. Please note: if you do not want to answer one or more of the questions in this questionnaire, please leave them blank and move on to the next question. The questionnaire is designed to be completed electronically by a project team member, during or following an interview with a compost producer/growing media manufacturer, or electronically by a compost producer/growing media manufacturer. The boxes will expand as they are being completed. If the questionnaire is to be filled in on paper, then the document should be altered (boxes should be expanded by adding lines within them) prior to printing in order to allow sufficient space for writing in them.

Organisation Details

Organisation Name

Respondent Name

Contact details


Nature of business or organisation (please tick those that apply)

PAS 100 Compost producer Growing Media Manufacturer

1. Scale of Production

Cubic metres produced of PAS 100

compost (different grades) and/or

growing media (GM) types or range

Geographical supply

area

Proportion of UK market?

(%) if known

Sector:

Expanding (E)

Declining (D)

Static (S)

e.g. 11,000 m3 of 0 – 10 mm green

compost;

15,000 m3 of peat-free multipurpose

GM;

3,000 m3 of reduced peat-free

propagation GM.

e.g. UK (not

Scotland) and

republic of Ireland

e.g. ~ 5% of retail market

for bagged growing media

e.g. E

2. Do you use sell PAS 100 compost in its own right or as an ingredient in growing media, and on what scale?

(Please describe what you do briefly)

3. Please give an indication of the extent to which the following factors or issues affect your sales or use of

PAS 100 compost in growing media. Tick the box which matches your current thoughts.

This issue

prevents me

from

selling/using PAS

100 compost in

growing media

This issue

limits my

sales/use of

PAS 100

compost in

growing media

This has been an

issue for us in the

past but is not

any more

This has never

been an issue for

us


pH

High bulk density


Weed seeds


Compost shelf life

Consistency of product


Customer requirements

Other (please specify)


4. The following is a list of potential benefits of including PAS 100 compost in your growing media mix.

Please tick the one box per row to indicate which matches your current thoughts.

Agree Neither agree

nor disagree

Disagree

Source of slow release nutrients

Less moss/liverwort on pot tops

Lower cost per m3 compared to other ingredients

Soil-borne disease suppression

Better moisture retention

Lower lime and base fertiliser requirement

Better buffering of nutrients

To meet recycling targets

Carbon footprint

Other benefits, please name

5. The characteristics of PAS 100 compost can vary between suppliers. Could you please tell us the range of

values you expect from the PAS 100 compost you supply and/or use (they could be more stringent than

the requirements of the PAS 100 certification scheme). NB: If you do not have the correct figures to hand,

simply comment on any problems you have in sourcing composts with appropriate characteristics for the

parameter of concern).

Parameter Units Value you

expect for

parameter

Comments on your ability to source

compost with appropriate value for the

parameter

Physical contamination % m/m

pH pH Units

High bulk density g/l

High electrical conductivity EC µS/cm

Weed seeds %

Sciarid flies and other pests Present/absent

Compost shelf life Months

Consistent product? Yes/No

Microbiological safety no. of CFU/ml

Other (if not named above)


6. Do you have any further comments on your (or your compost supplier’s) ability to achieve the above values

7. If you have managed to resolve one or more of the key issues that were causing problems in the past OR if

you have ideas as to how they might be overcome, please comment below.

How you managed to resolve

undernoted issue (if relevant)

How do you think this issue could be

resolved in future?


pH

High bulk density


Weed seeds


shelf life of end product



Other (if not named above)

8. If you have not used PAS 100 compost and do not intend to do so please let us know why? (Please give as

much detail as possible)

9. Do you have any other comments/discussion points you would like to raise on compost use in growing

media:


10. Are you aware of the following publications (yes or no)

WRAP good practice guide (Compost production for use in growing media)


WRAP Guidelines for the specification of quality compost for use in growing media


11. What would allow or encourage you to consider recommending/using compost or more compost in growing

media? – for example, data or information on specific benefits from using PAS 100 composts, trials results

where composts have been used successfully to grow specific plant types, further details of the PAS

scheme, changes to the PAS scheme, changes to the WRAP good practice guide, improved Guidelines for

the specification of quality compost for use in growing media, recommendation from a respected authority,

or something else?

Please tick this box to indicate that you are happy for us to attribute the comments below directly to you within the final report. Please tick this box if you are happy for us to use your comments but would like to remain anonymous Thank you for taking the time to communicate your views on the use of compost within growing media. Your help is very much appreciated. Please return to [email protected]



mailto:[email protected]


B) Questionnaire on the use of BSI PAS 100 Compost in growing media (for growers)



Organisation Name

Respondent Name

Contact details


1. Nature of business or organisation

Main type of operation

Geographical spread and scale

Type of clients? (e.g. wholesale [e.g. to

multiple retailers or other nurseries] or

retail [e.g. to gardeners, landscapers etc.]

Where do you get your growing media

(GM) from (e.g. mix your own or buy from

named GM manufacturer)?

If you buy in your GM, does it contain PAS

100 compost? (yes, no or don’t know)

If it does not contain PAS 100 compost,

why not? (e.g. because supplier does not

offer it, or because you do not want it, or

because your supplies does not recommend

it to you)

If your GM does contain compost, can you

comment on why you are using this (or

these) blend(s) (e.g. because you want to

reduce peat use or because your supplier

recommended it)

2. Crops covered

No. of pot plants/plant types (e.g. propagation material

[seeds/cuttings], liners, larger pot sizes and approximate

types grown (e.g. bedding, pot plants, alpines,

herbaceous, shrubs, trees, edible crops in modules/pots)

Proportion of UK

market? (%)

Market Value if

known? (£)

Sector:

Expanding (E)

Declining (D)

Static (S)

3. Please give an indication of the extent that the following factors affect whether you use growing media

which contain PAS 100 compost. Tick the box which matches your current thoughts.

This factor

prevents me

from using PAS

100 compost in

my growing

media

This factor

limits my use

of PAS 100

compost in

growing media

This factor has

been an issue for us

in the past but is

not anymore

This factor has

never been an

issue for us


pH

High bulk density


Weed seeds


Growing medium shelf life



Other (please name)


4. The following is a list of potential benefits of including PAS 100 compost in your growing media mix. Please

tick ONE box on the right for each row to indicate that you agree, disagree or are not sure whether the

statements on the left represent genuine benefits to you when compost is included in your growing media.

Agree Neither agree nor disagree

Disagree









Improved carbon footprint

Improved sustainability of growing medium


5. The characteristics of growing media which contain compost can vary between suppliers. Could you please

tell us the range of values you expect from the growing media you use? NB: If you do not have the correct

figures to hand, simply comment on any problems you have in sourcing growing media with appropriate

characteristics for the parameter of concern).

Characteristic Units Value Comments

Physical contamination % m/m

pH pH Units

High bulk density g/l

High electrical conductivity EC µS/cm

Weed seeds %

Sciarid flies and other pests Present/absent

Compost shelf life Months

Consistent product? Yes/No

Microbiological safety no. of CFU/ml

Other (please name)


6. If you have not used growing media which are partly based on PAS 100 compost and do not intend to do

so please let us know why? (Please give as much detail as possible)

7. Do you have any other comments/discussion points you would like to raise on compost use in growing media:

8. Are you aware of the following publications (yes or no)

WRAP good practice guide (Compost production for use in growing media)


WRAP Guidelines for the specification of quality compost for use in growing media


9. What would allow you to use or encourage you to use compost (or use more compost) in your growing media

– for example, data or information on specific benefits from using PAS 100 composts, trials results where

composts have been used successfully to grow specific plant types, further details of the PAS scheme,

changes to the PAS scheme, changes to the WRAP good practice guide, improved Guidelines for the

specification of quality compost for use in growing media, recommendation from a respected authority, or

something else?

Please tick this box if you are happy for us to attribute your comments directly to you in the report of our findings which will be submitted to WRAP and the SGMTF. OR Please tick this box if you are happy for us to use your comments but would like to remain anonymous Thank you for taking the time to communicate your views on the use of compost within growing

media. Your help is very much appreciated.

Please return to [email protected]





C) Questionnaire on the use of BSI PAS 100 Compost in growing media (for retailers)



Organisation Name

Respondent Name

Contact details


1. Nature of business or organisation

Main type of operation (Single site/multi-site)

Geographical spread (county, single country UK,

multi-country UK, multi country, Europe)

Type of clients (e.g. amateur gardeners,

professional growers)

2. Growing media (containing composts) sold

Approximately what percentage of total UK growing media sales is your company

responsible for (including your own branded and independent branded products)?

%

Do you consider the market for growing media based partly on PAS 100 composts to be

expanding (E), declining (D) or static (S)?

E / D / S

Products sold (please fill in a separate line below for each product sold, and the

percentage of compost in each)

% of compost

included

3. Please give an indication of the extent to which the following factors affect whether you are prepared to

sell growing media which contain PAS 100 compost. Tick the box which matches your current thoughts.

This factor

prevents me from

selling growing

media containing

PAS 100 compost

This factor limits

our sales of

growing media

containing PAS

100 compost

This has

been an

issue for us

in the past

but is not

any more

This has

never

been an

issue for

us

Am not

aware of

the issue


pH

High bulk density


Weed seeds

Sciarid flies and other

pests

Shelf life of product



Poor customer perception

Other (please name)


4. Please give an indication if the following potential benefits might make you consider asking for PAS 100

compost to be included within your growing media mixes. Tick the box which matches your current

thoughts.

Agree Neither agree nor disagree

Disagree Am not aware of this

potential

benefit









To improve carbon footprint/sustainability of growing

media

Specific requests from customers


5. If you do not sell growing media which contains PAS 100 compost and do not intend to do so please let us

know why?

6. Do you have any other comments/discussion points you would like to raise on growing media which contain

PAS100 composts in growing media:

7. What would allow or encourage you to consider buying and selling more growing media which contain

PAS100 compost – for example, customer pressure, promotion of compost-based media from television

programmes or gardening publications, readily available information on specific benefits from using growing

media based on PAS100 composts, trials results where composts have been used successfully to grow

specific plant types or something else?

Please tick this box if you are happy for us to attribute your comments directly to you in the report of our findings which will be submitted to WRAP and the SGMTF. OR Please tick this box if you are happy for us to use your comments but would like to remain anonymous Thank you for taking the time to communicate your views on the use of compost within growing media. Your help is very much appreciated. Please return to [email protected]


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