Questioning Peat Moss

Consider the environmental costs of using it.

December 22, 2010

Before the mid-1900s, peat moss was largely unavailable and unused by gardeners and farmers in the United States. In the decades since then, peat’s popularity has increased dramatically. And with it, an unanswered question: Is peat moss a responsible and sustainable choice for gardeners?

Peat is the partially decomposed remains of plants, most commonly sphagnum moss. It forms over many millennia in bogs, marshes, and swamps—known as peatlands or peat bogs—often gaining less than a millimeter in depth every year. The process is simple but very slow.

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As sphagnum moss grows on the surface of a bog, the older parts of the plant are submerged in oxygen-poor water. The lack of oxygen slows decomposition dramatically, preserving the moss and anything else that falls into the bog. Given enough time, submerged sphagnum moss forms the dense, absorbent material known as peat moss. Left alone, the process won’t stop there. Although the transformation requires eons, undisturbed peat will eventually form coal. Peat is essentially young coal—a baby fossil fuel. And, like all fossil fuels, it is rich in carbon.

A 2009 article in the journal Science makes the claim that, “meter for meter, peatlands store more carbon than any other terrestrial ecosystem.” All told, the world’s peat bogs store approximately 562 billion tons of carbon—more than all the trees in the world, and roughly equivalent to half the carbon currently in the atmosphere as carbon dioxide, or CO2. Healthy peat bogs accumulate an additional 110 million tons of carbon every year, more or less. All this despite the fact that peat bogs cover only 3 percent of Earth’s land and freshwater surface.

When peat is mined, this stored carbon is vulnerable to release into the atmosphere, where it contributes to the problem of global climate change. Whether used as a soil amendment or a fuel source, peat releases its stored carbon when it decays or burns. Additionally, because peatlands must be drained of their water before the peat can be mined, the bogs also release carbon during the mining process. The International Peat Society reports that some mined bogs continue to exhale carbon into the atmosphere long after the completion of mining, often despite habitat-restoration attempts.

Climate change and carbon emissions are not the only issues here. There is also the question of sustainability. Almost all horticultural peat sold in the United States is imported from Canada, which has a wealth of peatlands and other wetlands. More than 11 percent of Canada is covered by peatlands, which account for more than 279 million acres of the nation’s total land and freshwater area. “Canadian Peat Harvesting and the Environment,” a report sponsored in part by the Canadian Sphagnum Peat Moss Association, claims that Canada accumulates more than 77 million tons of peat every year. This is approximately 60 times the industry’s estimated annual harvest of 1.3 million tons of peat. A comparison of these two numbers indicates that the Canadian peat industry mines just 1.7 percent of the peat produced naturally every year—arguably a responsible quantity. However, the situation is not that simple.

Only a fraction of Canada’s peatlands are suitable for commercial extraction. Most Canadian peat-mining operations are located in the southern provinces, where ready access to roads and population centers reduces the costs of transportation and ensures the availability of a work force, electricity, and other resources. A large percentage of peat bogs may simply be too remote to support peat extraction on a commercial scale.

In addition to geographic accessibility, a commercially viable peat bog must supply enough high-quality peat to justify the expense of mining. In most cases, the horticultural-quality peat deposit must have an average depth of at least 2 meters to be considered worth the effort. The bog must drain readily—an essential step in the mining process—and be located in a region where occasional dry spells facilitate the peat-drying process.

These limitations raise a question: Of Canada’s 279 million acres of peat bogs, how many are actually suitable for mining? This unanswered question is key, because only those bogs that can be developed should be included in any sustainability calculation.

Sphagnum moss grows so slowly that management for sustainable use is a significant challenge. At the average rate of 0.6 to 0.7 millimeter per year, Canadian peat bogs add 6 to 7 centimeters in depth (less than 3 inches) over the course of a century. It will require 3,000 years to amass the 2-meter depth needed to justify the costs of extraction. Under these conditions, a fully mined peat bog will not be able to support a second “harvest” for at least 3,000 years.

Can a resource that renews itself this slowly ever be considered sustainable? If we balk at cutting down 500-year-old trees in old-growth forests, should we accept the extraction of 3,000-year-old sphagnum moss from peat bogs?

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