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Remember to provide drainage for the extrawater coming off the roof. One option is to collect

the water for irrigation. If there is not adequateslope to move the water quickly away from thegreenhouse, provide drainage pipes. The mostcritical time will be the spring thaw, which is alsowhen the greenhouse will be full and there will belittle time to dig drainage ditches.

Biernbaum, MSU, Organic Greenhouse Transplants; 1/12/06, page 1 of 13

Greenhouse Organic Transplant ProductionJohn A. Biernbaum, Department of Horticulture, Michigan State University

IntroductionGreenhouse grown flower, herb and

vegetable transplants create a wide range ofproduction and marketing opportunities. Whetheryou are just starting with transplant production orbuilding on past experience, there are several areasof greenhouse management to consider. The firsttopic is the greenhouse structure and equipmentwhich includes planning and selecting a design thatwill provide the necessary temperature and lightintensity. The second area is the management oflight and temperature for transplant production.The third area ofroot zone management includesthe growing container, the root media, and themethod of providing water and nutrients to the rootzone. If the first three areas are properly managed,we won=t have to worry much about the fourth:

insect and disease management.The goal is to present the important

considerations related to transplant production.Many of these are the same regardless of whetherthe transplants will be certified organic. The rootmedia, fertilizer and pest control considerations aremore important for organic certification. Cropspecific schedules will not be presented.

Part I. Structure and EquipmentManaging the greenhouse atmosphere toprovide appropriate light and temperatureconditions depends on design, covering materials,heating, cooling and ventilation. For the small-scale farmer, the availability of capital to investmay limit the options.

Site Selection and LayoutLocate the greenhouse to maximize light

interception. At latitudes above 40, the standard

recommendation is to orient the greenhouse withthe ridge running east and west so that winter lightis penetrating the length of the south side of thegreenhouse, not from the end. Consider shadingfrom trees and buildings. To avoid shading, locatea distance equal to at least twice the height of theshade source. Buildings attached to greenhousesare located on the north side to prevent shading.

Design and MaterialsDuring visits to small-scale diversified

vegetable farms and CSA=s I have seen a wide

range of structures used for transplant production.Greenhouse vs cold frame, free standing vs lean-to,heated vs unheated, commercial vs home made;there are many possible options. Decision makingdepends on the monetary investment possible,

available space, and the relative dependence onhuman verses mechanical environmental regulation.Most commercial structures will be of

galvanized steel pipe or square tubing. Metal endwalls and side rails cost more but avoid the issue oftreated lumber. The use of wood is influenced bythe desire to not use treated lumber, although somecertifying agencies differentiate between wood incontact with the ground (not allowed) vs wood usedabove ground (may be allowed). For hoop housesconstructed at MSU, we avoided the use of treated

lumber by attaching end wall posts to metal fenceposts driven into the ground. We raised the 2"x4"pine baseboards off the ground and attached areadily available 24" x12' fiberglass panel so it wentinto the ground and provided a wind buffer andsomething to drop the roll down side against. Inother projects where there were more fundsavailable, we purchased and constructed all metalend walls and frames. While manufactured metalendwalls cost 3 or 4 times what wood costs, it lookslike a good investment if funds are available.

The most likely covering material will bedouble layer inflated 3-4 year polyethylene film.Plastic films must be greenhouse grade, nothardware or construction grade. The second mostcommon small farm option is a rigid, single ordouble wall polycarbonate or acrylic. While glassgreenhouses are not likely justified for on farmtransplant production, glass windows, sliding patiodoors, or glass shower doors can be used for coldframe construction for hardening transplants.


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Forced air, natural gas or propane unitheaters are the most common form of heat for smallgreenhouses producing transplants. One limitationwith this design is getting heat down near the plants.Plastic perforated convection tubes can be used toblow warm air beneath benches. Benches withplastic or solid tops and sides can also be located infront of a heater. With cold soil floors it isrecommended that flats be separated or lifted off thefloor. Bottom heat using hot water circulated

beneath the flats is a very efficient way ofmaintaining growth while keeping air temperaturescool and can be provided with readily availablewater lines, water heaters and circulating pumps.


The shape of the roof will influence lightinterception. For polyethylene covered structures,the rounder Quonset designs with a flat spot on topare being replaced by a more peaked or gothicdesign. The higher roof angle increases winter lightinterception, decreases summer light interception,often increases peak height, helps with snow andcondensate removal from the roof, and is highly

recommended. Gothic designs come in two pieceswhich makes shipping easier and less expensive.

SizeThe primary factors determining size are the

desired function, cost/budget, location or spaceavailable, method of ventilation and cooling,method of heating and fuel requirement. For thesake of providing some perspective, example sizesrelative to small farms and transplant growersmight be Asmall@: less than 1000 square feet (20' x

50'); Amedium@: 2000 up to 4000 square feet (20'or 30' x 100' or more than one); and Alarge@:

greater than 5000 square feet . In 1000 square feetat 80% growing space efficiency (a full house), atleast 400 flats (11" x 22") or 28,800 (72 cell flats) to80,000 (200 cell flat) transplants can be grown.

Ventilation

If passive (vents only) ventilation will beused instead of exhaust fans (active ventilation) thegreenhouse should be smaller to allow easiercooling. Widths of 20 to 30 feet and lengths of 40to 50 feet are common. The larger the vent area, theeasier it is to cool but usually the harder it is toclose up to keep warm when necessary. If roll upsides are used, longer structures can be cooledwithout fans. Retractable roof designs are alsobecoming more popular because of the ventilationand cooling possible.

Heating

CostsComplete commercial greenhouses

including the structure, utilities, environmental

controls, floors, benches, irrigation equipment etcrange in cost from as little as $5 per square foot upto $25 per square foot. The upper end mightinclude a glass structure with hot water heat. Thecost for the least expensive hoop structure withnothing else added can be between $1.00 and $2.00per square foot for a 30 x 100 greenhouse that is notassembled. Having something assembled orconstructed typically doubles the cost. Shippingcosts can also be significant and might be avoidedby looking for the most local source.

Greenhouse management can be very simpleand low tech or very detailed and mechanized.Take the time to learn the key concepts first andsave money both in the short and long run. If youare going to build your own greenhouse, take thetime to work out how you will integrate lightintensity control, ventilation/cooling, and heating.There are choices to be made about the level andcost of mechanization verses the level of laborinput. If you are on the farm (home) most of thetime and available to alter vents and shading by

hand, the need for automated vents and therefore thecost will be lower. If you don=t want to be tied to

the greenhouse, invest in thermostats andventilation equipment.

When planning a greenhouse for the smallfarm, it is important to take into consideration thetime and labor cost of planning and constructingpersonal plans or modifications as opposed topaying extra for a complete kit with all the parts. Ifcapital is limiting and labor is not, there are lowcost ways of building and operating a greenhouse.If however labor and time are the limiting factor,the extra cost invested in materials and havingsomeone else build it can usually be justified by thevalue of the product coming from the greenhouse.

Part II. Light and Temperature

Managing the greenhouse to provideappropriate light and temperature conditions forquality transplants depends on understanding how


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plants respond to light and temperature.

Transplant Growth StagesTransplant or plug production is generally

described in four observable stages. The first twostages account for actual seed germination andemergence. Stage one includes the starting processfrom seed sowing and medium wetting to the

emergence of the radical or root initial. Stage twocontinues from root emergence until theseed/cotyledon leaves are expanded. Stage threeoccurs when the primary growth phase of trueleaves and an extensive root system develops.Stage four is the finishing or hardening stage. Ingeneral, the recommended moisture level andtemperature tend to decrease and the amount oflight and fertility will increase with the progressionof each stage.

Light ManagementOptimal seed germination may depend on

the absence or presence of light, although mostspecies will germinate in light or dark. Only lowintensity light (50 to 100 foot candles) is necessaryfor the first stage of germination. High intensity(direct, full sun) is usually avoided because itcauses excessive heat or rapid drying of the growingmedium. Many large plug producers usegermination chambers during stage one toefficiently maintain temperatures (70 to 75 F) and

moisture levels. It is critical that light intensity beincreased during stage two to prevent the rapidelongation that occurs, sometimes in matter ofhours, as the hypocotyl (shoot) emerges from thesoil. A stretched or etiolated hypocotyl will makethe remainder of transplant production moredifficult.

The question of whether to cover or not tocover the seeds with root medium is usually lessdependent on light and more dependent on howmoisture will be maintained. Covering is notessential but helps maintain moisture. Tiny seedslike petunia, begonia or trachelium are usually notcovered. Additional germination medium is mostcommonly used when a covering is needed.

The initial stages of germination are verydependent on soil temperature (as opposed to airtemperature). Soil temperature is influenced by theamount of light and the rate of moisture evaporationfrom the root media, which is influenced by relative

humidity. Evaporation from media is significantlygreater than transpirational water loss by the plantin the early stages of germination and plant growth.Soil temperature is also influenced by the color andtype of growing container.

When considering greenhouse lightmanagement, light intensity (brightness measured infoot candles), duration (measured in hours), and

quality (color or wavelength) are all concerns.Acceptable transplants can be grown under a widerange of light intensities, but the largest (weight, notheight) transplants will be grown under the highestlight intensities. For late spring and summerproduction, shading may be necessary, not to blockan excess of light, but rather to reduce heat in thegreenhouse. If ventilation is not adequate to reducetemperatures, shading compounds can be sprayedon the covering or shade fabrics can be used outsidethe greenhouse.

The amount of plant growth will bedetermined by both the intensity of the light and theduration of time the light is available. Forexample, if light quantity were considered, theexpected result would be similar plant growth if5,000 footcandles were provided for 5 hours or2,500 fc were provided for 10 hrs. The product ofboth is 25,000-footcandle hours. This helps explainwhy good transplants can be grown under afluorescent shop light if the light is kept close to theplants and left on for 18-24 hrs/day. It also helps

explain why greenhouse plants do not grow as muchduring the winter when light intensity is low anddays are short. High-pressure sodium (HPS) lamps(400 watt) are most efficient for supplementallighting in greenhouses, and the most efficient useis in early stages of growth (stage two and earlystage three) when plants are small and many plantsare concentrated in a small area. A well placed lightwill also help increase the temperature in a smallarea of the greenhouse.

Light quantity influences the effect ofnitrogen fertilizers on plant growth. Ammonium(NH4

+) toxicity may occur under very low light and

cold soil (less than 55F) conditions. For the plant tomake use of ammonium nitrogen, there must beadequate production of sugars and carbohydratesfrom photosynthesis. Low light, together with lowtemperatures (see next section) that can occur in thewinter greenhouse combined with uniquerequirements of early seedling growth can lead to


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problems. A limited number of high intensitysodium lamps (HPS) in a walled off corner of thegreenhouse can provide the extra light and warmthneeded at a low cost.

It is generally assumed that plants get talleror stretch in lower light. For most plants, however,there is not an increase in height with lower lightintensity unless there is a change in light quality, for

instance due to crowding or shading by other plantsor the greenhouse covering. When plants are tightlyspaced, the light quality or ratio of red to far redlight changes as plant leaves absorb light. This canlead to increased plant height caused by longer stemsections between the leaves. More space betweenplants due to larger containers or more space on thebench means shorter plants.

Temperature ManagementRelationships between day and night

temperature, the 24-hour average daily temperature,and the temperature response of the plant speciesbeing grown, are important considerations to overalltemperature management.

Average Daily Temperature (ADT). Ingeneral, the 24-hour average daily temperature willhave the greatest influence on the rate of plantgrowth. Most plant species grow very little attemperatures less than 45 to 50 degrees Fahrenheit(F) and will continue to grow more rapidly up to a24 hour average of 75 to 77 F. The rate of growth

can be characterized as the rate of increase inweight of the plant, or the rate of formation of newleaves. Cool season vegetables like lettuce, spinach,cabbage, broccoli, etc will grow under temperaturesnot suitable for warm season vegetables like tomatoor vine crops. The variation in growth rate withtemperature also applies to cut flowers. An averagetemperature range for stage 3 would be 60 to 65F.

Greenhouse temperatures also have an effecton nutrient availability from organic fertilizers orcompost based media. The mineralization ofnitrogen and the conversion of ammonium nitrogento nitrate nitrogen are dependent on the activity ofsoil microorganisms. At soil temperatures of 55Fand above, nutrient and nitrogen availability areusually adequate and increase as plant growthincreases. However, the soil warms more slowlythan the air after a cold spell and the recovery timefor the microorganisms may be longer than for theplant. Bottom or soil heat is highly recommended

for seed germination and transplants if airtemperature is maintained below 55F.

Day/Night Difference (DIF). Consideringhow day and night temperatures vary can help indetermining how the plant will look. When the dayis very warm and the night is cool or cold, plantswill be taller. If the day and night temperature areboth the same, plants will be shorter than with warm

days and cool nights. If the night temperature in thegreenhouse is kept warmer than the day temperatureby using heating at night and ventilation during theday, the plants will be even shorter. Keeping daytemperatures cool (70F) will help keeptransplants shorter. The relationship is referred toas DIF, or difference between day minus night.

Relative Humidity and CondensationLight, temperature and ventilation will also

influence the moisture in the air. High relativehumidity limits nutrient uptake and increases thepotential for foliar and flower diseases.Condensation on the roof covering can alsodramatically reduce light intensity. Ventilation toremove moisture will usually precede attempts toconserve energy or heat in the greenhouse.

Hardening Finished Plants

The transition from the greenhouse to thefield involves changes in light, temperature and

wind. A gradual transition over a few days withsome protection from wind and temperature but fullexposure to light can increase the survival rate oftransplants in the field.

Part III. Root Zone ManagementIrrigation water quality, irrigation method,

root medium, and fertilizer all interact to define theroot zone. For transplant production, the usuallyvery limited root volume and the variety ofcontainer sizes and materials also play a majorfactor in managing the root zone. Rapidly growingplants with limited root volumes require carefulwater and nutrient management to provide a healthytransplant with proportioned root and shoot growth.

Growing containersTransplants can be grown in all types and

sizes of containers including no container at all ifsoil blocks are used. Before the routine availability


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But what is most economical and efficientfor the small grower producing a wide range ofdiversified crops? Efficiencies of plug production

are partially based on specialty propagatorsproducing large numbers of flats of fewer speciesand cultivars. Plug production is less an advantagewith production of smaller numbers of a widediversity of crops. Other questions to ask includewhether labor in March, April, and May will be alimiting factor for the small farm like it is in acommercial flower greenhouse? Will the

greenhouse space need to be filled and emptiedmore than once to be profitable like in a commercialflower greenhouse?


of plastics, transplants were successfully grown inwooden flats and roots were simply pulled or cutapart at transplanting. Plastic or foam trays allowfor less transplant shock and ease of handlingindividual plants with intact root balls. But theycan also add to materials cost and be a disposalproblem if recycling is not an option. Pressed peatpots are readily available in a variety of sizes but I

have not seen many specific examples of their usefor vegetable transplants. A decision will have tobe made regarding whether germination andfinishing will occur in the same container orwhether germination will be done in one containerfollowed by transplanting to a finishing container.

Seed Germination. My experience with thecommercial bedding plant greenhouse was entirelyplug oriented. Even Asmaller@ growers use some

type of mechanical seeder that individualizes seedinto cells or plugs. From hand held needle

seeders run with vacuum pumps, to inline needleseeders, to drum seeders, there is a wide range ofoptions. Plug technology is over 30 years old andhas been driven by the need to minimize labor andcrop time while maximizing space efficiency.Shorter crop time and more time at high densityplant spacing allow multiple Aturns@ of the

greenhouse which greatly increases profitability.The organic transplant producer has to considerhow critical these factors are for them.

Germination and a longer growth period insmall plugs followed by shorter finishing times inlarger cells does require more attention to detailthan germination in open flats for shorter times andlonger times in finishing flats. However,germinating and growing in 800, 600, 500 and 400cell trays is the most challenging and probably bestleft to specialty propagators. If transplants will bedirect sown and finished in 200 - 128 cell or largertrays, Aplug@ production is much easier to do and

might better be called transplant production.Plug production techniques have evolved

based on soilless root media and frequentapplications of primarily nitrate nitrogen watersoluble fertilizer. Compost based root media andless frequent application of water soluble organicfertilizers like fish emulsion can be successfullyused for plug production.

Standard flat inserts with 20 rows are oneefficient way of producing a large number ofspecies. These are used for transplant production inthe MSU trial gardens were one 48 cell flat of over1500 different crops are desired. These flats requirevery little germination root media. Crops withsimilar germination times should be grouped withina flat. If watering is a concern, or the time from

sowing to transplant will be longer, individual 4 or6 inch pots can be used for sowing seeds. Withplugs or any germination container, the smaller thecell, the more frequent the need for water.

Transplants. A review of research regardingsize and age led the authors to conclude thatinconsistencies in experimental techniques and awide range of variables resulted in no specificrecommendations to make regarding a Abest@ age

or plant size. Larger or small root balls, younger orolder transplants, there are many acceptableapproaches.

One key distinction that can be made iswhether or not the plants are stressed or treated tofavor the induction of flowering. For ornamentalbedding plant transplant production, the marketdemands miniature plants in flower even thoughlong term garden performance would likely befavored by more vegetative transplants. Droughtand low nitrogen are frequently used to controlplant size and initiate early bud set. This strategywould produce a totally unacceptable transplant forcut flower production. For field grown cut flowersit is important that growth not be checked or flowerinitiation encouraged prematurely.

What about vegetable transplants? Theanswer is most likely dependent on the market anddesired result. For early but limited yield that mightbe desired for a homeowner vegetable garden,tomato and pepper transplants in larger containerscan be stressed to induce early flowering. But for


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field production the goal will be to put a vegetativeplant out and promote rapid vegetative growth thatwill produce the largest yields.

Production costs will likely be a primaryfactor influencing transplant size. Tomatoes andpeppers in 4 inch pots do great when transplanted.But where is the greenhouse space or labor neededto handle such large transplants?

Root mediaPhysical Properties. While plants can be

grown in all types or root media, seed germinationand transplant production have perhaps the greatestrequirement for a high quality, uniform medium. Itis sometimes noted that coarse or large particle sizemedia are desirable due to the need for highaeration during germination. However, mostgermination media are actual fine with smallparticle size in order to provide uniformity for

filling small plug cells. Aeration is maintainedinstead by not over watering or saturating the rootmedium.

Chemical Properties. Nutrient levels in agermination medium need to be low but balanced.Excess soluble salts can reduce water uptake anddamage young roots. Recommended electricalconductivity values are 0.4 to 0.6 mS for a 1:2 soilto water sample or less than 1.0 for a saturatedmedium extract (SME). The root medium pHshould also be in the range of 5.5 to 6.5, although

many species will germinate over a range of 5.0 to7.5.

Biological Properties. The presence of plantpathogens is also a primary concern sincegerminating seedlings are very susceptible to rootrot fungi. This is perhaps the main reason given forusing soilless or peat-based media for seedgermination. Compost is far from sterile but can beused for seed germination. Given these basicguidelines, the selection of root mediumcomponents and amendments together with fertilizerwill likely have the greatest impact on whethertransplant production is suitable for organiccertification.

Components. Components are the materialsused to provide the base media, and are present atrates of at least 10% by volume. Commoncomponents such as peat, perlite, vermiculite,coconut coir, and bark are acceptable for organiccertification. Compost is the most renewable and a

preferred organic substrate.Peat: In my experience, peat is the leading

transplant media candidate. There are many gradesof peat and for potting media. Usually the bestCanadian sphagnum grade available is worth theinvestment (Sungro, Fafard, Premier). Limingrecommendations are different when more or lesspeat or different types of peat are added (5 to 10 lb

per cubic yard range for 70% peat medium).Coconut Coir: Another material like peat is

coir. It is a renewable substrate like peat, but it istransported much further. It does work great forgrowing plants and has good water and air holdingproperties. The level of soluble salts (EC) would beexpected to be higher than peat as would the pH.We choose between peat and coir depending on thepH of the compost.

Compost: Well made compost can havephysical properties (air and water holding) similar

to peat. However, the nutrient content would bemuch higher. It is also critical to recognize thedifference in pH. While peat is often very acidicand requires the addition of lime, compost is oftenbasic when first finished, but usually neutral whenfully mature. We choose the mixture of peat andcompost primarily based on attaining the desiredpH. For the compost I have made from gardenwaste, straw, hay and sheep/horse manure, a 50/50blend of peat and compost has yielded a pH ofaround 6.0 which is desired for a potting media. At

pH of 5.8 to 6.3, phosphorus will be much moreavailable, particularly if there is little or no soilpresent. Sieving or screening the compost helpsprovide a more uniform product. Compostfeedstocks and maturity determine pH and the pHmust be tested.

When it comes to making compost forpotting medium, one could refer to a process ofmaking designer composts. The quantity neededis not large, and the impact on the overall farmproduction can be very large. Transplants play sucha key role that making compost specifically fortransplants makes sense.

Following is an example of a non manurecompost recipe for transplant production (orcompost tea). The goal is to use readily availablematerial that would be affordable and reasonablyconstant across geographic regions.


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1 bale straw1 bale grass hay or grass alfalfa mix1 bale wood shavings for bedding1 bale (3.8 cu ft) peatmoss6 cubic feet (wheel barrow) of soil6 cubic feet (wheel barrow) of grass clippings (Ifgreen plants are not available use alfalfa hay.)6 to 12 cubic feet (wheel barrow) of green plants

like comfrey, weeds without seeds, greenmanure, etc.

We make this mixture by layering thecomponents in a small manure spreader and thenletting them come out the back in a pile. Water isadded during layering and while the material isdischarge from the manure spreader. This mixturereached over 140F in four days and held atemperature above 130 for one week or more. Thepile was put back into the spreader for mixing.

Alfalfa meal was added (25 lbs or 5 gallon bucket toabout 4 yards) to assure a rapid second heat. Thismixing was done in June and July when green plantmaterial was readily available.

The mixture was kept moist and allowed tomature through the remaining part of the summer.The piles were covered and left outside for thewinter. Ideally the material would be brought intothe greenhouse in the fall to be ready for springtransplants. Fertilizers such as rock phosphate orgreensand could be added during composting or

when the compost is brought in for the winter(although it is not likely needed). These materialshave low solubility and may not contribute much,but they definitely will not hurt things and end up inthe field with the transplant.

Perlite and Vermiculite: Coarse componentslike perlite or vermiculite are usually added becausethey help maintain airspace under conditions of fineparticle peat or compost and improper irrigation.However, with quality peat and compost, they maynot be needed for aeration. The level of soluble

salts in the compost may be high enough that perliteand or vermiculite are needed to lower soluble saltconcentrations to ranges acceptable for seedgermination.

Bark and Sand: Based on my experience todate, even aged or composted pine bark would notbe recommended because of the tendency to tie upnitrogen, which usually is in short supply withorganic fertilizers. Nitrogen tie up with bark is not

a problem with synthetic fertilizers because it iseasy to add a little more N. While sand is often stilllisted as a possible component to add aeration, itrarely contributes to adding pore space in alreadyporous media. The potential for chemical anddisease contaminants are other reasons to not usesand.

A likely problem with peat-based media is

the low nutrient content and holding capacity. Withthe addition of slowly soluble or available fertilizers(listed later), and water soluble fertilizers, organicfertilization can be accomplished. However, theaddition of compost can significantly increasenutrient retention and capacity and is highlyrecommended.

Amendments. Examples of commonamendments (less than 10% by volume) to peat-based media are lime, fertilizers (potassium nitrate,superphosphate, micronutrients), wetting agents or

other additives. Synthetic fertilizers and wettingagents routinely added to peat-based media are notacceptable for organic certification. Wetting agentsare needed primarily when peat is very dry. Oneoption is to not allow the peat to get very dry.Another consideration is that other components likecoconut coir, perlite and vermiculite wet withoutwetting agent. Sand also can help increaserewetting. If the peat is moistened with warm waterwhile blending during formulation with othercomponents, it is likely a wetting agent is not

necessary. Peat does vary in wettability.Formulations. The recommendation to date

is for a blend of peat and compost or peat-basedsoilless medium and compost. The currentgreenhouse standard unit of measure foramendments is pounds added per cubic yard ofmedium (3' x 3' x 3' = 27 cubic feet). Amendmentsare not essential but can include: blood meal(nitrogen), rockphosphate (phosphorus andcalcium), greensand (potassium and micronutrients)and other sources in the table provided. ElliotColeman recommends combining equal parts ofthese three (although he does not state equal partsby volume or weight, we assumed volume), andthen adding a rate equivalent to 14 lbs per cubicyard to a peat or peat-based medium and compost(50/50 by volume) blend. He recommends lettingthe blend sit for a month or more before using,although he does not state that this is essential.This or similar formulations were very effective for


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us with edible flowers and herbs.The cost of commercial peat-based media

typically ranges from $50 to $75 dollars per cubicyard in bags or bales ($2.00 to $2.50 per cubicfoot). Assuming peat at $1 to $1.25 per cubic footand perlite and vermiculite at $1.50 to $2.00 percubic foot, component costs alone for a 70% peatmedium would be $30 to $40 dollars per cubic yard.

To add the Coleman recommended organicnutrients assuming bloodmeal @ $28/50 lb,greensand @ $6.75/50 lb, and rock phosphate @$7.50/50 lb would cost $5 per cubic yard (plus thecost of lime). Additional costs would be equipmentand labor. What is the cost (or value) of qualityhome made compost?

Coleman mentions mixing the media andfertilizers in the fall which results in allowing themixture to sit for some time before use. During thefall of 1999 we grew poinsettias with several

organic fertilizers in comparison with syntheticfertilizer. Poinsettias transplanted into media withsoybean or alfalfa based fertilizer were initiallystunted or killed. Fresh plants replanted into thesame medium which was remixed after two weeksgrew fine. After incorporating plant derivedfertilizers (soybean meal, alfalfa meal) there is anoticeable amount of fungal growth during theinitial breakdown. Our recommendation is to addadequate moisture for decomposition to occur andallow the medium to sit for 2 to 4 weeks before

planting. Soak amendments like pelleted alfalfaprior to adding to insure adequate moisture.

Bradfield Alfalfa Fertilizer. Based on anumber of greenhouse studies, Bradfield NaturalFertilizer (www.bradfieldind.com) can be added topeat-based soilless media or potting mediacontaining compost or soil at a rate up to 10 to 20lbs/yd3 to add complete nutrients that last over 2 to3 months. The alfalfa based fertilizer also suppliescarbon based compounds that can stimulatemicrobial activity in the root medium.

For alfalfa-based pellets like BradfieldFertilizer (3-1-5), the nitrogen/nutrient availabilitymight be in the 15% to 30% over the first twoweeks but there is not good data to know for sure.The continued availability would depend onmicrobial activity in the potting media, moistureavailability, and temperature. There might begreater nitrogen availability in a medium withcompost or soil at 10 to 30% by volume (usually

increased microbial activity) compared to a peat-based medium.

In our research we started with a high rate of40 lbs Bradfield Fertilizer /yd3 of root medium (24oz or 672 gram per ft3). Assuming 3% nitrogen,this rate would provide about 10 times the amountof total nitrogen as the potassium nitrate rate (1lb/yd3) given above. We are assuming that about

10% of the nitrogen is immediately available. Thisrate was not used for seed germination but for atransplant medium for growing impatiens and otherbedding plants. We had good results with this rateand grew impatiens for up to 12 weeks withoutadditional fertilizer. We did not add other fertilizersfor phosphorus or micronutrients. We did add limeto peat-based soilless medium but not the compostmedium.

There are a number of factors that caninfluence results and nutrient availability as

mentioned above. We did see greater nitrogenavailability in a medium containing compostcompared to a peat-based soilless medium. We didnot do rate comparisons with Bradfield Fertilizer.A comparison of our rate to the manufacturers rateindicates that we were much higher than therecommended rate. A rate of 4 tsp/gallon asrecommended in the literature is approximatelyequal to one gallon (5 lbs) of fertilizer per cubicyard. A garden rate on the bag is 25 lbs per 1000ft2which would equal 2.5 lbs per 100 ft2 or cubic yard.

(Similar rates are often recommended for 100 ft2 or1 cubic yard of medium.) Our rate of 20 to 40lbs/yd3 is almost 10 times the manufacturesrecommended rate. A rate of one-half of the rate weused might be a better starting point 20lbs/yd3 or12 oz per cubic foot or even 10lbs/yd3. Based onthe density of Bradfield fertilizer (5 lbs/gallon), thiswould equal about 1 pint fertilizer in volume percubic foot root medium.

The cost of a quality peat-based pottingmedium is in the range of $40 to $80 per cubic yard.At $15 per 50lb bag, the addition of Bradfield at the20 lb/yd3 rate would add about $6 per cubic yard.(At 480 6 azalea pots/yd3, the cost per pot is 1.25cents per pot.) This is much more expensive thanpotassium nitrate, but what is achieved is a muchlonger term dose of nitrogen and other beneficialeffects on microbial activity. When organiccertification of the root medium is required, theBradfield fertilizer is a valuable addition. The
http://www.bradfieldind.com/http://www.bradfieldind.com/


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Bradfield fertilizer also provides adequate P and K

Water Soluble FertilizersWith the use of synthetic water-soluble

fertilizers and mechanical injection devices(proportioners), fertilization is one of the easiestaspects of large scale greenhouse production. ForOrganic certification, there are materials available

but few specific, published recommendations. Witha well prepared root medium, only nitrogen (N) willlikely require management during production.While some phosphorus (P) and potassium (K) canbe added, it is N that has the greatest effect on plantsize. (Assumes calcium (Ca), magnesium (Mg) andsulfur (S) are in the root medium or water.

Fish Emulsions. We have used soilless peat-based medium and coconut coir without syntheticfertilizer added and only fish emulsion (5-1-1) usedas fertilizer for periods of several months up to

almost a year without any apparent nutrientdeficiencies. Use of fish emulsion as a solefertilizer for potted plant production has been welldemonstrated by others, many years before we tried.Although I did not expect it to work due to the lowP and K content.

For a 5-1-1 liquid formulation, a dilutionrate of 1 to 100 (1 gallon in 100 gallons or 6.4ounces in 5 gallons) will provide 500 ppm. (1%liquid equals 10,000 ppm) A dilution rate of 1to1000 will provide 50 ppm N. The best rate is in this

range and will be determined by the N levels in theroot medium, the desired growth and the frequencyof application. When a fertilizer injector isavailable and rapid growth is desired, fertilization atevery irrigation with low rates like 50 to 100 ppm Nis common. However, with products like fishemulsion that have a fragrance to contend with,fertilization at biweekly or monthly frequency ispreferred. Interval fertilization also prevents overfertilization. Fertilization can be delayed until theplants show signs of lower leaf yellowing or slowedgrowth that indicates more N is needed. A finalshot of N just before transplanting may bebeneficial.

Omega 666. We have also worked withOmega 666, a water soluble blend of digestedorganic fertilizers purchased from Harmony Farmsin California (also available from Peaceful ValleyFarm Supply (www.groworganic.com) . While thecost for 5 gallons of 6-6-6 was over $200, the

material could be diluted as much as 1000 times tomake 60 ppm N which would cost 4 cents pergallon. At 600 ppm applied every two or threeweeks, the cost would be 40 cents per gallon dilutedmaterial. By comparison, synthetic water solublefertilizer like 20-10-20 @ $20/25lb bag applied at600 ppm N would cost 2 cents per gallon dilutedsolution. Buying small quantities at $2.00 per pint,

fish emulsion costs 19 cents per gallon to apply at600ppm N (1.5 fluid ounce per gallon water). A 5%N solution at 1:100 will provide 500 ppm N.

All the organic nitrogen applied is notreadily available as with synthetic fertilizers. Theproper rate to apply must be based on looking at theplant and considering the temperature andbiological activity of the root medium. Nitrogenavailability from organic fertilizers is expected to bequicker with compost and soil containing mediacompared to peat-based soil-less medium.

Applications of organic fertilizers are not expectedto show the rapid 1 to 2 day growth response seenwith synthetic fertilizers. Synthetic fertilizers areprimarily nitrate nitrogen which can be immediatelyused by the plant. Organic fertilizers are primarilycomplex nitrogen like protein which must first bebroken down to ammonium nitrogen(mineralization) or ammonium nitrogen which ischanged to nitrate nitrogen by bacteria(nitrification). Ammonium can be used by theplant directly, particularly rapidly growing plants in

high light. But most nitrogen is taken up as thenitrate form. Too much ammonium nitrogen in lowlight (February, March) or cool soil conditions(


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necessary, components are reasonably available butexpensive in small quantity.

#3. Peat lite media as above with lime, blood mealor alfalfa meal for nitrogen, rock phosphate forphosphorus and green sand or organic approvedpotassium sulfate for potassium. Rates asrecommended by Eliot Coleman. . Or consider

Bradfield Alfafa Fertilizer. Water soluble organicfertilizer, usually fish emulsion, applied as needed.This method adds some nutrients to the rootmedium so everything is not dependent on liquidfertilizer application. Requires purchasing theorganic nutrient sources and making sure the rateand method of application are correct.

#4. Mature, well-balanced on-farm compostblended with peat, (and possibly perlite and orvermiculite if aeration needed) to provide a medium

with good aeration and water retention and all thenutrients to grow and finish the transplants (andperhaps help in the field also). Nutrients such asalfalfa, alfalfa meal, any organic approved nutrientsource can be incorporated during the compostingprocess. Lime is generally not necessary withcompost but check the pH. Requires makingcompost the summer before transplant production.Compost will mature during the fall and then can bestored for use in the spring. Compost must havegood physical, chemical and biological properties.

Irrigation

Water Quality. For a detailed discussion ofwater quality issues related to greenhouseproduction, refer to the chapter 5 in the bookTips ofGrowing Bedding Plants published by the OhioFlorists Association. Water quality refers to theconcentration and species of chemical elementsfound in water that make it suitable or unsuitablefor irrigation. In general, the shorter the crop time,as for transplants, the less effect water quality willhave on plant growth. However, it is also true thatthe smaller the growing container and the morefrequent the irrigation, the greater the effect ofwater quality. It is important to have your wateranalyzed and to know what desired or undesiredelements are present and how they will effect yourchoice of root media and fertilization.

Method of Application. The success orfailure of plants in a greenhouse is most often

attributed to the person handling irrigation. Theprimary questions to be addressed are When towater, How much or what volume to water, andWhat method of application to use.

When to water will change over time. Inearly stages of seed germination it is critical thatmoisture availability be very high. Once rootgrowth begins, moisture levels are gradually

reduced over time. In finishing stages transplantsmay be wilted on purpose.

How much to water refers to whether or notto partially moisten the root media, thoroughlymoisten the root medium, or water enough so excessdrains from the root medium (leaching). Standardrules of watering to thoroughly saturate or leach atevery irrigation do not apply to seed germination ortransplant production. Root medium air space inshallow containers is maintained more by howmuch water is added than by the particle size of the

root medium. Leaching is also not recommendedunless soluble salt levels are excessive. Usually theintent is to retain as much of the nutrients in the rootmedium as possible, particularly with organicproduction methods and the small root mediumvolume.

Choices of how to water include overheadwatering using hose and breaker or sprinklers versessubirrigation by flooding from below. Making surethe foliage is dry at the end of the day is importantin the later stages for disease control. The best

system may be one that combines overheadirrigation in the early stages and subirrigation in thelater stages.

If water is going to be used to regulate plantsize, it is important to recognize that there is morethan one way to grow plants dry. One way is towater plants thoroughly and then allow them to dryuntil wilting occurs. This method does not reduceplant height nearly as much as frequent, lightapplications that do not saturate the root mediumand keep the plant under a constant low level ofdrought stress.

Part IV. Pests and Diseases

It is totally within the realm of possibilitythat if your farm or greenhouse is relativelyisolated, the greenhouse has been empty and at lowtemperatures over the winter, you have not overwintered plants in the greenhouse, you start strictlywith seeds, as opposed to purchased cuttings, your


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In the first year of our research with edibleflowers and herbs, we battled the white fly andthrips primarily by releasing purchased predators orparasites. The second year we used what welearned previously to keep the whitefly and thripwithin acceptable levels, but the aphids were amajor problem. We used more predators andoccasional sprays, which were suitable for organiccertification but were as hard on the purchasedpredators as they were on the pests. The third yearwe did not have any major outbreaks but we hadsome problems with spider mites and potentiallydevastating problems with mealy bug. For the

previous mentioned research, we were located in alarge greenhouse range of over one acre with manydifferent research projects and crops. In general allthe pests were present and chemical applicationswere heavy. We were an island in the middle andfairly constantly under scrutiny as a source of pestsbecause we were not spraying chemicals. Cropswere in the greenhouses year round.


potting medium doesn=t harbor any noxious pests

and diseases, you don=t over water or over fertilize

your transplants, and you minimize crop time in thegreenhouse, that you could never see or experienceany of the following pests and diseases. The bestinsect and disease management program in thegreenhouse is based on a strong defense and a wellthought out plan. A good starting place for basic

information about integrated pest management inthe greenhouse is the article available on theATTRA web site (attra.org).

A good starting recommendation is to usethe best cultural methods as outlined in the previoustwo sections and grow a healthy transplant. Themuch published and referred to pest and diseasecontrol triangle includes the environment, the hostand the infesting or infecting agent. Start with agrowing environment providing proper light andtemperature conditions that favor growth of the

plant and minimize the growth of the insect ordisease. For example, warmer temperatures meanfaster growing transplants, but will also meangreater potential for pest populations to develop.The third part of the triangle is knowing as much aspossible about the pest or disease.

PestsIdentification. Based on experience with

large, commercial greenhouse operations the tenmost common greenhouse pests could be rated thisway. The three that present the largest, routineproblems are white fly, thrip, and fungusgnats/shore flies. The next three that are occasionalproblems or more crop specific problems are aphid,spider mite, and leaf miners. Less common but stilla problems with certain crops are mealy bug, scale,chewing caterpillars and slugs.

In years since the experience describedabove, working in three separate greenhouses thatwere more open to the outside and not surroundedby other greenhouses being sprayed, insectproblems have not been a major concern. We havediscontinued all work with releasing predators. Forthree years we have been able to manage withminimal applications of soap to wash plants with ahose end sprayer and the occasional application ofneem or Pyganic for aphids, whiteflies or thrips.Improvement in our fertility management may have

something to do with the reduced insect problems.Management. Perhaps one of the best

recommendations is to minimize transplant croptime. Schedule carefully so plants are not in thegreenhouse any longer than necessary. The longerthe production and or holding time, the greater theprobability for uninvited guests to move in.

An option in the greenhouse, particularly forshort term crops like transplants, is to use eitherprotectant or biorational pest control sprays: (spraysbased on naturally occurring control agents or

competitors). Examples of sprays acceptable fororganic certification by at least some certifyingagencies include insecticidal soap (Ex. M-Pede),Buavaria fungus (Ex. Botanigard), neem basedproducts (Ex. Neemx, Azatin ), garlic or hot pepperbarriers, compost teas and herbal or mineralpreparations.

We have experimented with most of theseoptions. Effective timing and methods ofapplication that allow thorough coverage are veryimportant for success. Repeated applications atappropriate intervals are almost always necessary toreduce or eliminate a developing pest population.

Diseases

While healthy growing transplants are oftenresistant to infection by the ever present root rotfungi, the initial phases of seed germination and theearly stages of seedling growth are perhaps the mostsusceptible parts of the plant life cycle. If root rot


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pathogens are present at high levels, plant lossescan be complete.

Root rot pathogens potentially present inroot media in conventional greenhouses aregenerally controlled by careful selection of the rootmedium, watering practices that minimize over orunder watering, and use of selective fungicides thattarget a fairly narrow range of fungi. The use of

selective fungicides is very important in routinelarge scale greenhouse production and widelypracticed. This practice is not acceptable fororganic transplant production. The techniques ofsteam or chemical sterilization (kill everything) oreven pasteurization (kill most of the bad guys) areno longer commonly practiced in most commercialgreenhouses. While there are authors thatrecommend baking or heat treatment of seedgermination media, the practice is not practical toaccomplish and of questionable value.

Germination and transplant mediaformulated from sphagnum peat, perlite andvermiculite will generally not require any additionaltreatment. The level of innoculum present in peat istypically low and perlite and vermiculite are sterileas a result of the manufacturing process. If compostis to be added, the composting procedures should betested for the suitability to clean the compost ofseed (root rot) pathogens. When the heat ofcomposting (130-150 F) is maintained for adequatetime (2 to 3 days) and the entire pile is heated at

some time via mixing and reheating, the resultingcompost should be fine for germination mediaassuming the quality and maturity are satisfactory.

Identification. The most commonrecognized greenhouse root rot pathogens arePythium andRhizoctonia. Also problems at timeswith specific crops are Phytophthora, Fusariumand Theleviopsis. The most common recognizedgreenhouse foliar fungal pathogens are powderymildew andBotrytis. The most common bacterialpathogens in the greenhouse are Erwinia,Pseudomanas and Xanthomonas. The mostcommon viral pathogen in commercial greenhousecurrently is impatiens necrotic spot virus (INSV)which is transmitted by thrips. When soil is used inthe greenhouse, nematodes could also be a concern(not likely).

Management. As previously stated, the bestcontrol for root rots is proper formulation of theroot media, proper watering, and fertilization

practices that favor healthy, undamaged roots.Foliar fungal pathogens are best minimized bykeeping relative humidity in the greenhouse low(


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water carefully. Add more fertility if needed, butdont add too much. Keep an eye out for pests andproblems and handle them quickly.

References and Sources of InformationOrganic Plug and Transplant Production. ATTRA HorticultureProduction Guide.

The New Organic Grower. Elliot Coleman. Published byChelsea Green. Cost $24. Contact Chelsea Green PublishingCo. PO Box 428, Gates-Briggs Bldg #205, White RiverJunction, VT 05001. 800-639-4099.

Byczynski, Lynn. 1993. Growing great transplants. Growingfor Market. February p. 1-4.

National Greenhouse Manufacturers Association.http://www.ngma.com Provides contacts and links for mostmajor North American greenhouse manufactures.

Planning and building a greenhouse. Center for Agriculture

and Natural Resources Development. West Virginia University

Extension Services.

www.wvu.edu/~agexten/hortcult/greenhou/building.htmGreenhouse Operation and Management (5th edition). l998.Paul V. Nelson, Prentice Hall, Inc., Upper Saddle River, NJ07458 (SB 4l5.N44).

Greenhouse Engineering. 1989. Robert Aldrich and JohnBartok. Northeast Regional Agricultural Engineering ServiceNo. 33

Appropriate Technology Transfer for Rural Areas (ATTRA),

PO Box 3657, Fayetteville, Arkansas 72702. Phone: (800)346-9140. http://www.attra.org

Parnes, R., 1990. Fertile Soil, A growers guide to organic andinorganic fertilizers. AgAcces, Davis, CA. 190 p.

John BiernbaumDepartment of HorticulturePlant and Soil Sciences Building

Michigan State UniversityEast Lansing, MI 48824Not for publication.

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