Slide 1

Using woody garden waste to create seed compost (and other composts) Peter Harper CAT (by kind permission of Nerds Anonymous) Daft jokes by Adam Harper

Slide 2

What for? Dealing with your own organic waste is a significant contribution ordinary householders can make to sustainability Soft garden wastes and kitchen wastes are easy to compost, but woody wastes are not Some gardens produce an awful lots of awkward woody material Bonfires are not cool I thought that perhaps woody waste compost would have distinctive and useful properties So I undertook a long-term programme of research and observation on the breakdown of woody wastes, and how to use the resulting material

Slide 3

First trial Two adjacent open bunkers filled identically with randomly arising woody waste. Topped up and jumped on for four years. Urine added on one side but not the other.

Slide 4

Intermittent inspections Archaeological tunnels dug into each bay At year 4 very little humification Dry conditions Water added at top either runs straight through or is shed off the sides Additions of urine seem to make no difference.

Slide 5

Section and detailed inspection at year 6 Humified zones Zone still unhumified

Slide 6

Three composts compared for seed germination Woody waste compost was easily the best Paper-mill de- inking sludge Seived woody waste Commercial John Innes Seed compost

Slide 7

Trial of pure woody waste as a general garden compost

Slide 8

Courgettes as test crop: rapid growth, good yields, healthy plants

Slide 9

Analysis of 7-year-old woody waste compost Determinand ValueUnitRemark Density500kg/m 3 Light pH7.1 Slightly high for some purposes Conductivity97S/cm Very low good! Dry matter31.9% Organic matter*66.3% High NO3-N29.4mg/l Low NH4-N1.5mg/l Low Total N *2.1% w/w Surprisingly high Total K*0.16% w/w Surprisingly low Total P*0.26% w/w Surprisingly low * Dry matter basis

Slide 10

But who cares about the analysis? It works It is the most brilliant lovely material Like fine malt whisky it is worth waiting for But if we could make it quicker, wouldnt that be nice? Lets think about why it takes so long

Slide 11

A Harpothesis Loose piles of woody material resist breakdown because they are too dry They are too dry because Excessive drainage (rain runs quickly through) Thatched roof effect (rain is shed on outer layers) Open texture allows ready evaporation Therefore decomposers (especially fungi) cannot boot up Therefore there is a long stuck phase that might go on for years

Slide 12

continued Eventually a focus of humification develops that can Hold moisture Act as a refugium and breeding-ground for decomposers A wave of humification propagates from that focus Thereafter, breakdown proceeds relatively quickly

Slide 13

Humified zones Zone still unhumified

Slide 14

Apparent progress of humification in an open woody heap 0% 100% Humification Time in years 13524 Initial phase of bacterial decomposition Stuck phase Adventitious formation of humification focus Rapid spread of humification

Slide 15

How to avoid getting stuck Compress to reduce voids Shredding Vertical stacking Prevent moisture escaping enclosure Add moisture-retaining materials Soft wastes Soil

Slide 16

Adam always loved Shreddies

Slide 17

Shredding produces some usable compost in 18 months An unseived mixture of all these grades has grown potatoes with good yields for four successive years But dreadful for slugs!

Slide 18

The Stack Principle 2 x 0.75 x 0.751.5 x 1 x 1

Slide 19

Design and function of the stack Solid plastic sides Opening at bottom Fresh material Fine material ready for use Open top >1.5m 1m Coarse pieces back to top

Slide 20

Trial of simple stack principle, using pure woody waste Woody waste added for one year till full, then left without further treatment for three further years Volume reduction Dismantling upper parts of container Builders bottom

Slide 21

Appearance of surface Surface removed

Slide 22

Results This supports the theory that compression and reduced moisture loss will accelerate humification. What about adding moisture-retaining materials?

Slide 23

Trial of stack principle plus addition of moisture-retaining materials Materials added randomly at top Green/woody Brown/woody Leaves Weeds Sods Spent composts Grass clippings (occasionally)

Slide 24

Results after two years Appearance of surfaceAppearance just under surface

Slide 25

Progressive removal of material Homogeneous breakdown right to the bottom

Slide 26

Close-up of texture Texture is less peaty, much more earthy

Slide 27

Conclusion This result supports the theory that adding certain extra materials further accelerates humification of woody wastes It also provides a no-hassle approach to composting all but soft wastes However.

Slide 28

We have two types of compost to test Pure woody material, peaty and springy Call it woody waste compost or WWC Mixed garden wastes with soil Call it soil stack compoist or SSC Trials are under way to compare them with each other and with high fibre compost, made with soft wastes at low temperatures (HFC)

Slide 29

Growing trials HFC wwc SSC

Slide 30

One rather clear result SSC is very weedy. WWC is remarkably unweedy. HFC is in between

Slide 31

Other early results SSC and WWC performed equally on potatoes and kale SSC outperformed HFC on cucumbers WWC was best for cabbages and lettuce HFC was best for leeks and winter onions SSC can propagate clubroot, WWC and HFC would not. WWC is especially attractive to mice and birds, who dig up newly-planted crops

Slide 32

IMPLICATION FOR HOUSEHOLDERS Households with larger gardens could benefit from at least two compost streams with different qualities All are simple to operate with low maintenance

Slide 33

Possible tests of Ingham hypothesis Elaine Ingham of soilfoodweb.com claims that composts based on woody materials would give better results on perennials, while cellulose-based composts are better for annuals So far, results do not support these hypotheses

Slide 34

Kitchen waste Grass clippings High Fibre method Fast, fine compost Other Garden wastes: Weeds Autumn leaves Spent composts Turf and sods Slow Stack method Slow, coarse compost for general purposes, Urine (optional!) Heavy woody waste Export to CA site for thermophilic composting Landfill Energy-from- waste Non- recyclable paper and cardboard Slow stack method with woody materials only Slow, fine material for seed compost and potting mixtures High-nitrogen wastes High-carbon wastes Principal pathways Variant pathways Woody wastes: Prunings Hedge trimmings Twigs Lignified stalks

Slide 35

THE END Centre for Alternative Technology