For Peat's Sake: Should You Be Concerned?
There are now readily available waste products at our disposal that can not only expand your substrate options, but help make use of materials that might otherwise plague the environment.
You probably know it as the best growing medium you can buy.
Among its many benefits, sphagnum peat moss offers excellent water and air exchange
capacity; provides ideal cation-exchange capacity; enhances root growth;
provides excellent buffering capabilities; saves water by retaining moisture
and releasing it slowly; saves on fertilizer by reducing nutrient leaching;
protects soil from hardening; adds organic material; and aerates heavy, clay
soil and binds sandy soil.
U.S. peat resources have been estimated at more than 110
billion tons, with more than 50 percent located in undisturbed areas of Alaska,
according to the United States Geological Survey (USGS). Florida, Michigan and
Minnesota are the highest peat-producing states, in order of quantity produced.
In 2002, 760,000 metric tons were produced domestically, with 95 percent of
that production absorbed by the horticultural industry. Peat produced in the
United States is typically classified as reed-sedge Hypnum peat, which has a
lower market value per ton than the weakly decomposed sphagnum peat from
Canada. Ninety-nine percent of U.S. peat imports from 1998-2001 came from
Canada, accounting for 50 percent of total domestic usage, according to Stephen
M. 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 approximately
510 billion tons. The development of new horticultural peat operations or
expansion of existing operations in the United States has become increasingly
difficult, as numerous federal, state and local wetlands protection regulations
apply to permitting, harvesting and reclamation of peat bogs. The cost of
compliance and the time required to obtain the proper permits have caused some
smaller producers to stop harvesting peat. The USGS anticipates that domestic
peat demand will continue to grow at a steady rate for the near future, with
Canadian peat accounting for a greater percentage of U.S. consumption.
So just what is a peat bog, anyway? In short, it is a
special type of wetland. A "peatland" is a wetland on which extensive
organic material has accumulated, the rate of which can be as much as 1-2 mm
per year (4-8 inches per century). Peatlands are defined by a minimum
accumulation of 16 inches; as the peat layer accumulates, access to nutrients
in the underlying soil is reduced such that the vegetation must obtain its
nutrient requirements from groundwater seepage. Peat accumulation can occur
when climatic and other physical conditions result in a rate of plant material
growth that exceeds the rate of decomposition. Peatlands may have trees -- or
not -- and species diversity tends to be low, most likely due to the acidic,
low base cation environment.
Approximately 99 percent of Canada's total national
production comes from the combined operations of 20 corporate groups that form
the Canadian Sphagnum Peat Moss Association (CSPMA). The majority of these
operations are located in southern and southeastern Quebec and eastern and
northeastern New Brunswick. Once a peatland has been selected, it is surveyed
and a drainage plan is prepared. Following the completion of ditches, surface
vegetation is removed and the deposit is ready for peat production. Drying the
surface peat layer requires the sun and wind -- which is why areas receiving
high precipitation are poor selections for harvesting -- and the topmost layer
is typically harrowed or "milled" to enhance the drying process.
After 1-3 days, the dry peat layer is collected using a large vacuum harvester
or other equipment, then is transported to a processing facility for screening
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. In
Canada, harvesting takes place on less than 17,000 of the country's total 113
million hectares of peatlands, according to the issues paper "Canadian
Peat Harvesting and the Environment," and as an overall resource there is
70 times as much peat accumulating as is being harvested each year in Canada.
When harvesting is completed on a bog, it is returned to a
functioning peatland under Canadian governmental regulations. Before harvest, a
producer must take all necessary steps to Á reduce impact on the
environment; record the flora and fauna present on the bog for restoration
purposes; and cooperate with local environmental groups. During harvest, the
producer must minimize the acreage being harvested; leave a buffer zone around
the bog; leave a layer of peat when harvesting stops; and design drainage
ditches so the water table can be restored. The primary goals after harvest are
to 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 offer
high-quality peat to North American suppliers well into the future. In Europe
and especially the UK, however, the situation is quite different. Whereas
Canadian 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 used
for horticulture, according to the UK's Peat Producers Association (PPA). A
current government target requires that 40 percent of the UK market be replaced
by peat alternatives by 2005, and it has been suggested that that figure be
increased to 90 percent alternatives by 2010, inciting staunch opposition by
the peat industry. At present, 40 percent of the peat used in the UK is
produced domestically, while 60 percent is imported, primarily from Ireland.
Judging from the major impact that environmental groups have
had on other industries in Europe, such as genetically modified seeds and food
products, there is reason to believe that in the future, the UK's target for
peat alternatives could conceivably increase beyond the 40 percent previously
cited. Should that happen, there is the possibility that the country would have
to look beyond Ireland for peat imports. That place could be Russia, Germany or
Finland, 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 of
Arkansas, offers a good reason to consider alternatives: increasing the arsenal
of growing media. "Hopefully, we'll find things that are locally and
regionally available for growers to use effectively that are cheaper. If you
look at what goes into a greenhouse operation, growers don't tend to have
control over many costs--but one of the areas they could potentially tweak is
in their growing media." Here are a few peat and perlite alternatives you
may have heard of, and some others coming down the pipeline.
Coir. Evans has done
a 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-holding
capacity. It also tends to have a higher pH than peat, reaching into the
5.0-6.0 range. High-quality coir should be brown, not green or yellow, which
would indicate newer, fresher coconut; coir with a high proportion of new
rather than decomposed material can cause nitrogen tie-up, according to Evans.
Coir is also susceptible to higher salt levels both because coconut trees
naturally extract salt from the soil and because of low-quality processing.
There are two things that Evans advises growers to watch out
for when using coir. First, when it's wet, it should act like a sponge, not
coffee grounds. Its consistency has to do with the compression ratio and
moisture level the producer used when the coir was manufactured; if the
material 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 and
absorbs water readily. Second, do a quick pH and EC test, in case you should
end up with a low-pH batch.
In Evans' coir research, everything from poinsettias to
bedding plants has performed similarly to those grown in sphagnum peat; there
have even been reports of increased root growth with the use of coir and of
fungus gnat control. Coir does seem to exhibit disease-suppression capabilities,
particularly of Pythium and Phytopthora. Evans believes that some chemical
compound is responsible for this characteristic, as coir is loaded with
phenolic compounds -- the natural chemicals plants produce to defend themselves
against disease. Unfortunately, the suppression Evans has seen has not been
entirely consistent in experiments using ratios of 80 percent coir and 20
Despite its benefits, there is no cost savings associated
with using coir because it ships from such faraway places as Sri Lanka and the
Philippines -- this is perhaps the one issue that has limited the growth of the
coir industry for horticultural applications.
Compost materials. Kim Moore, an associate professor at the
University of Florida's Ft. Lauderdale Research and Education Center, has
focused on the use of compost materials, and particularly, on locally available
sewage sludge combined with yard trimmings. "Something like compost is
really 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 -- the
water-holding capabilities and that beginning nutrient charge -- so I've found
I can cut my fertilization back when I use the sewage sludge-type
While Moore believes this type of compost holds a lot of
potential, it also poses two setbacks. First, it can be difficult to get a
consistent product every time, and second, it's not always locally available,
which means the cost could be greater. Some growers in South Florida are using
this product as a partial replacement to peat and as a supplement to
fertilizer. Moore says she's been able to achieve plant performance of equal
quality in her experiments with the sewage sludge compost compared to those
grown in Pro-Mix or Metro-Mix.
At Mississippi State University, Associate Professor Richard Harkess has done
extensive research with earthworm castings generated from horse, cattle and
sheep manure. "Some plants did fantastic; in fact, most plants with 20 percent
worm castings mixed in with peat moss and perlite did wonderfully. We even grew
some poinsettias where we didn't have to fertilize the crop for the entire
production cycle -- that was with a fairly high concentration of
The type of worms used for their castings are Eisenia
fetida, and are capable of consuming up to their bodyweight each day. The type
of 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 is
unpalatable for some reason -- in fact, in Harkess' studies, the worms would
either avoid it, or they'd die within a few days. Horse manure contains high
levels 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 [with
horse manure castings]," Harkess commented.
Cattle manure is more stable than horse manure because the
cellulose is thoroughly digested in a cow's four-chambered stomach; however,
because cows extract most of the nutrition from their food, the resulting
castings tend to be less nutritionally dense. Plants in Harkess' experiments
still grew successfully in cow manure castings despite their lessened
Growers can produce their own earthworm castings with the
help of a large bioreactor designed for culturing these worms. "You put
fresh 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 castings
off the bottom," Harkess explained. There is also the possibility of an
industry being created for these castings. Harkess says he could imagine this
being in cooperation with a feedlot somewhere or a local stockyard. "This
market is untapped and undeveloped in a lot of ways. Plants respond very well
to it, and castings fit into the whole organic gardening movement," he
Fresh rice hulls.
While you've probably heard of using dried rice hulls as a soil amendment and
alternative to perlite, you may not have thought of fresh ones -- perhaps
because there is a standing opinion that they cause nitrogen tie-up. In Evans'
trials with geraniums, tomatoes and pansies, however, there have not been any
nitrogen issues. Rice hulls are almost entirely silica, with a small amount of
lignan. They have a higher air-filled pore space, provide more drainage and are
much cheaper than perlite. Aside from all that, fresh rice hulls are abundantly
available as a waste product, with virtual mountains of them in Arkansas,
Louisiana, Mississippi, Texas and California. "We've replaced perlite with
fresh 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 cheaper
than perlite," Evans said.
Keeping your options open
You may be more than satisfied with your crop performance
using sphagnum peat moss products, and Canadian producers' efforts to keep peat
bogs sustainable should allay any environmental concerns you might have.
Nevertheless, it's important to remember that amid all of your fixed costs, you
still have options when purchasing your growing media. There are some viable
alternatives out there that may help you save money while maintaining the same
quality that peat has afforded you -- and at the same time, help you turn waste
into something useful.