For Peat’s Sake: Should You Be Concerned?
You probably know it as the best growing medium you can buy.Among its many benefits, sphagnum peat moss offers excellent water and air exchangecapacity; provides ideal cation-exchange capacity; enhances root growth;provides excellent buffering capabilities; saves water by retaining moistureand releasing it slowly; saves on fertilizer by reducing nutrient leaching;protects soil from hardening; adds organic material; and aerates heavy, claysoil and binds sandy soil.
U.S. peat resources have been estimated at more than 110billion tons, with more than 50 percent located in undisturbed areas of Alaska,according to the United States Geological Survey (USGS). Florida, Michigan andMinnesota are the highest peat-producing states, in order of quantity produced.In 2002, 760,000 metric tons were produced domestically, with 95 percent ofthat production absorbed by the horticultural industry. Peat produced in theUnited States is typically classified as reed-sedge Hypnum peat, which has alower market value per ton than the weakly decomposed sphagnum peat fromCanada. Ninety-nine percent of U.S. peat imports from 1998-2001 came fromCanada, accounting for 50 percent of total domestic usage, according to StephenM. Jasinski, a peat commodity specialist for the USGS.
World peat resources have been estimated at 2 trillion tons,of which the former Soviet Union has about 770 billion tons and Canada approximately510 billion tons. The development of new horticultural peat operations orexpansion of existing operations in the United States has become increasinglydifficult, as numerous federal, state and local wetlands protection regulationsapply to permitting, harvesting and reclamation of peat bogs. The cost ofcompliance and the time required to obtain the proper permits have caused somesmaller producers to stop harvesting peat. The USGS anticipates that domesticpeat demand will continue to grow at a steady rate for the near future, withCanadian peat accounting for a greater percentage of U.S. consumption.
So just what is a peat bog, anyway? In short, it is aspecial type of wetland. A “peatland” is a wetland on which extensiveorganic material has accumulated, the rate of which can be as much as 1-2 mmper year (4-8 inches per century). Peatlands are defined by a minimumaccumulation of 16 inches; as the peat layer accumulates, access to nutrientsin the underlying soil is reduced such that the vegetation must obtain itsnutrient requirements from groundwater seepage. Peat accumulation can occurwhen climatic and other physical conditions result in a rate of plant materialgrowth that exceeds the rate of decomposition. Peatlands may have trees — ornot — and species diversity tends to be low, most likely due to the acidic,low base cation environment.
Approximately 99 percent of Canada’s total nationalproduction comes from the combined operations of 20 corporate groups that formthe Canadian Sphagnum Peat Moss Association (CSPMA). The majority of theseoperations are located in southern and southeastern Quebec and eastern andnortheastern New Brunswick. Once a peatland has been selected, it is surveyedand a drainage plan is prepared. Following the completion of ditches, surfacevegetation is removed and the deposit is ready for peat production. Drying thesurface peat layer requires the sun and wind — which is why areas receivinghigh precipitation are poor selections for harvesting — and the topmost layeris typically harrowed or “milled” to enhance the drying process.After 1-3 days, the dry peat layer is collected using a large vacuum harvesteror other equipment, then is transported to a processing facility for screeningand packaging.
According to a 1999 International Peat Society (IPS) survey,Canada ranks second in global production of horticultural peat after Germany,producing approximately 22 percent of the world’s horticultural peat. InCanada, harvesting takes place on less than 17,000 of the country’s total 113million hectares of peatlands, according to the issues paper “CanadianPeat Harvesting and the Environment,” and as an overall resource there is70 times as much peat accumulating as is being harvested each year in Canada.
When harvesting is completed on a bog, it is returned to afunctioning peatland under Canadian governmental regulations. Before harvest, aproducer must take all necessary steps to Á reduce impact on theenvironment; record the flora and fauna present on the bog for restorationpurposes; and cooperate with local environmental groups. During harvest, theproducer must minimize the acreage being harvested; leave a buffer zone aroundthe bog; leave a layer of peat when harvesting stops; and design drainageditches so the water table can be restored. The primary goals after harvest areto restore the bogs to wetlands and reclaim bogs for beneficial crops.
The arguments for peat sustainability in Canada are sound,and with governmental monitoring in place, Canadian peatlands will offerhigh-quality peat to North American suppliers well into the future. In Europeand especially the UK, however, the situation is quite different. WhereasCanadian peat is used almost exclusively for horticultural purposes, in the UK,66 percent of harvested peat is burnt as fuel, while only 33 percent is usedfor horticulture, according to the UK’s Peat Producers Association (PPA). Acurrent government target requires that 40 percent of the UK market be replacedby peat alternatives by 2005, and it has been suggested that that figure beincreased to 90 percent alternatives by 2010, inciting staunch opposition bythe peat industry. At present, 40 percent of the peat used in the UK isproduced domestically, while 60 percent is imported, primarily from Ireland.
Judging from the major impact that environmental groups havehad on other industries in Europe, such as genetically modified seeds and foodproducts, there is reason to believe that in the future, the UK’s target forpeat alternatives could conceivably increase beyond the 40 percent previouslycited. Should that happen, there is the possibility that the country would haveto look beyond Ireland for peat imports. That place could be Russia, Germany orFinland, but it could also be Canada — which would drive up prices for U.S.importers as well as consumers.
Michael Evans, an associate professor at the University ofArkansas, offers a good reason to consider alternatives: increasing the arsenalof growing media. “Hopefully, we’ll find things that are locally andregionally available for growers to use effectively that are cheaper. If youlook at what goes into a greenhouse operation, growers don’t tend to havecontrol over many costs–but one of the areas they could potentially tweak isin their growing media.” Here are a few peat and perlite alternatives youmay have heard of, and some others coming down the pipeline.
Coir. Evans has donea fair amount of research with one of the most common peat alternatives, coir.Composed of coconut hulls, coir works very well as a growing media component,although it varies from sphagnum peat in some of its properties. Most notably,it has a slightly lower air-filled pore space but a higher water-holdingcapacity. It also tends to have a higher pH than peat, reaching into the5.0-6.0 range. High-quality coir should be brown, not green or yellow, whichwould indicate newer, fresher coconut; coir with a high proportion of newrather than decomposed material can cause nitrogen tie-up, according to Evans.Coir is also susceptible to higher salt levels both because coconut treesnaturally extract salt from the soil and because of low-quality processing.
There are two things that Evans advises growers to watch outfor when using coir. First, when it’s wet, it should act like a sponge, notcoffee grounds. Its consistency has to do with the compression ratio andmoisture level the producer used when the coir was manufactured; if thematerial was too dry when it was compressed into bales or blocks, the tiny,sponge-like cells will collapse, and cannot re-expand. Good coir expands andabsorbs water readily. Second, do a quick pH and EC test, in case you shouldend up with a low-pH batch.
In Evans’ coir research, everything from poinsettias tobedding plants has performed similarly to those grown in sphagnum peat; therehave even been reports of increased root growth with the use of coir and offungus gnat control. Coir does seem to exhibit disease-suppression capabilities,particularly of Pythium and Phytopthora. Evans believes that some chemicalcompound is responsible for this characteristic, as coir is loaded withphenolic compounds — the natural chemicals plants produce to defend themselvesagainst disease. Unfortunately, the suppression Evans has seen has not beenentirely consistent in experiments using ratios of 80 percent coir and 20percent perlite.
Despite its benefits, there is no cost savings associatedwith using coir because it ships from such faraway places as Sri Lanka and thePhilippines — this is perhaps the one issue that has limited the growth of thecoir industry for horticultural applications.
Compost materials. Kim Moore, an associate professor at theUniversity of Florida’s Ft. Lauderdale Research and Education Center, hasfocused on the use of compost materials, and particularly, on locally availablesewage sludge combined with yard trimmings. “Something like compost isreally a very good product — it can replace part or almost all of the peat.What I like about it is that it has a lot of the properties of peat — thewater-holding capabilities and that beginning nutrient charge — so I’ve foundI can cut my fertilization back when I use the sewage sludge-typecompost.”
While Moore believes this type of compost holds a lot ofpotential, it also poses two setbacks. First, it can be difficult to get aconsistent product every time, and second, it’s not always locally available,which means the cost could be greater. Some growers in South Florida are usingthis product as a partial replacement to peat and as a supplement tofertilizer. Moore says she’s been able to achieve plant performance of equalquality in her experiments with the sewage sludge compost compared to thosegrown in Pro-Mix or Metro-Mix.
Earthworm castings.At Mississippi State University, Associate Professor Richard Harkess has doneextensive research with earthworm castings generated from horse, cattle andsheep manure. “Some plants did fantastic; in fact, most plants with 20 percentworm castings mixed in with peat moss and perlite did wonderfully. We even grewsome poinsettias where we didn’t have to fertilize the crop for the entireproduction cycle — that was with a fairly high concentration ofcastings.”
The type of worms used for their castings are Eiseniafetida, and are capable of consuming up to their bodyweight each day. The typeof manure used does matter; for example, chicken manure is too high in ammonia,so worms will crawl out of it rather than into it, and hog manure isunpalatable for some reason — in fact, in Harkess’ studies, the worms wouldeither avoid it, or they’d die within a few days. Horse manure contains highlevels of undigested cellulose in it, which remains even after processing.”If you have a long-term crop, you’re going to see your soil shrink [withhorse manure castings],” Harkess commented.
Cattle manure is more stable than horse manure because thecellulose is thoroughly digested in a cow’s four-chambered stomach; however,because cows extract most of the nutrition from their food, the resultingcastings tend to be less nutritionally dense. Plants in Harkess’ experimentsstill grew successfully in cow manure castings despite their lessenednutritional value.
Growers can produce their own earthworm castings with thehelp of a large bioreactor designed for culturing these worms. “You putfresh manure in, usually about an inch at a time, and as the worms consume it,you add another inch, and the worms consume it, and you take the finished castingsoff the bottom,” Harkess explained. There is also the possibility of anindustry being created for these castings. Harkess says he could imagine thisbeing in cooperation with a feedlot somewhere or a local stockyard. “Thismarket is untapped and undeveloped in a lot of ways. Plants respond very wellto it, and castings fit into the whole organic gardening movement,” hesaid.
Fresh rice hulls.While you’ve probably heard of using dried rice hulls as a soil amendment andalternative to perlite, you may not have thought of fresh ones — perhapsbecause there is a standing opinion that they cause nitrogen tie-up. In Evans’trials with geraniums, tomatoes and pansies, however, there have not been anynitrogen issues. Rice hulls are almost entirely silica, with a small amount oflignan. They have a higher air-filled pore space, provide more drainage and aremuch cheaper than perlite. Aside from all that, fresh rice hulls are abundantlyavailable as a waste product, with virtual mountains of them in Arkansas,Louisiana, Mississippi, Texas and California. “We’ve replaced perlite withfresh rice hulls, and it’s working beautifully — plants do very well in it.Regardless of what they come up with in price, it’s going to be a lot cheaperthan perlite,” Evans said.
Keeping your options open
You may be more than satisfied with your crop performanceusing sphagnum peat moss products, and Canadian producers’ efforts to keep peatbogs sustainable should allay any environmental concerns you might have.Nevertheless, it’s important to remember that amid all of your fixed costs, youstill have options when purchasing your growing media. There are some viablealternatives out there that may help you save money while maintaining the samequality that peat has afforded you — and at the same time, help you turn wasteinto something useful.