Urban Gardening

Peat Moss in the Garden: Is it Sustainable?

Ponds in this restored bog are essential to the development of peat.
Ponds in this restored bog are essential to the development of peat. (Photo courtesy of Canadian Sphagnum Peat Moss Association)

Nothing is as simple as it seems. Case in point: peat makes a great growing medium that many gardeners rely on for everything from seed starting to amending garden soil. But there's concern that horticultural demands for peat could be endangering the natural peatlands. Gardeners typically want to be environmentally conscious. We wonder if we're contributing to the demise of peatlands. Should we continue to use a product that might damage precious natural habitats?

First, let's review some definitions. Peat is an organic material comprised of dead vegetation (leaves, stems, roots, trunks) that has partially decomposed in a water-saturated, oxygen-poor environment. Peat is acidic, absorbent, and low in nutrients.

Peatlands are wetland ecosystems where peat is formed. Water accumulates or seeps in through rainfall, springs, or surface flow. In cold climates, peat is typically formed from mosses. In tropical climates, peat consists mostly of trees. Other wetland plants, such as sedges, grasses, shrubs, and reeds, contribute to peat formation in both climates. The lack of oxygen and soil microbes in peatlands suspends the normal decomposition that occurs in your garden.

Unique Habitat

Virgin peatlands contain as much as 95 percent water. They act as huge water filters, removing toxins and metals. They store rainwater and slowly release it throughout the year, which helps maintain flow in streams and rivers during dry times. Conversely, during rainy times their amazing ability to absorb water reduces storm water runoff and downstream flooding.

Peatlands also play a critical role in global warming. They are the largest terrestrial carbon sink, holding more carbon than all forests or grasslands. They cover only 3 percent of the land, but contain 30 percent of the carbon.

Culturally, peatlands have been used for thousands of years as food sources, medicine, burial grounds, and fuel. Cranberries, lingonberries, and hortleberries grow abundantly in bogs and are still harvested there today. The sterilizing and preserving properties of sphagnum peat have been known and exploited throughout our history. Ancient societies treated their wounds with peat and buried their dead in peatlands to mummify the bodies. Archaeologists are able to fill in pieces of the human history puzzle from these anthropological treasures.

The most common use of peat has been as a fuel. The high concentration of carbon makes peat more efficient than wood as an energy source. In fact, if given a few million years and appropriate geologic forces, peat will transform into coal. Today many countries still use dried peat for fire. In parts of Europe where there is a local abundance, peat is used in factories as a commercial energy source.

Harvesting of Peat

Today in the northern hemisphere, the highest demand for peat is for horticulture. Peat has the perfect properties for a growing medium: abundance of pore spaces for air and water, lightweight, relatively weed-free and disease-free, and easily obtained. If plants need more nutrients or a higher pH, other substances can be mixed with the peat without losing the beneficial qualities. Horticultural researchers are working to create a comparable growing medium from bio-wastes and synthetics. But as of today, nothing matches the beneficial properties and cost efficiency of peat.

Moss will tolerate a few companions like these trout lilies, but it can be smothered by plants and leaf litter.
Regrowth in a harvested peat bog will eventually form the peat of the future. (Photo courtesy of Canadian Sphagnum Peat Moss Association)

Peat is renewable and will regrow if harvested in moderation. But as with many natural resources, peat collection is often done exhaustively. Drainage ditches are cut around the peatlands. Once the water drains, the peat is dug out, leaving pits or empty fields. Some countries fill in the space with agricultural crops, agri-forest, or retention lakes. This irreversibly changes the habitat, reduces the numbers of endemic peatland species, releases carbon into the atmosphere, and alters the hydrology. (Some rivers and streams stopped flowing in Scotland when a peatland was drained for a forestry project, and extensive and expensive restoration efforts are under way.)

So what's an environmentally conscious gardener to do? Peat is major component of nearly all soil-less mixes. Experts, including myself, recommend these peat-based mixes, particularly for containers and as a soil amendment in urban gardens. Are we encouraging people to destroy rare habitats just so our container plants can have extensive root systems?

We can relax.

Fortunately, 95 percent of the sphagnum peat moss available in the United States comes from the Canadian Sphagnum Peat Moss Association (CSPMA). This organization emphasizes sustainable harvesting practices and restoration efforts. Canada has 111 million hectares (about the size of Washington, Oregon, and California) of peatlands, but only 17 thousand hectares (comparable to the city of Portland) is actively harvested. Of the 70 million tons of sphagnum peat naturally created every year in Canada, only 1.3 million tons are harvested. To me, that's an example of sustainable management.

After harvesting, fields are reseeded” with live, shredded sphagnum. The wetlands are restored back to a functional state and allowed to grow naturally. They won't look the same for another thousand years, but the commitment to restore the peatlands' properties assures that the habitat is not lost.

The CSPMA commissioned a study on the carbon emissions related to sphagnum harvest. The University of Calgary's Department of Geology determined that CSPMA's removal of sphagnum peat only contributed 0.006 percent of the world's total carbon emissions or 0.1 percent of Canada's emissions.

After researching the issue, I believe the harvesting of peat moss is approached with the right mix of commerce, conservation, and restoration. I will continue to recommend sphagnum peat moss as a soil amendment and use it in my own gardens.

[Most of the data in this article come from the Coordinating Committee for Global Action on Peatland (CC-GAP), the Canadian Sphagnum Peat Moss Association (CSPMA), International Peat Society (IPS), and the International Mire Conservation Group (IMCG).]

For more info on Canada's sustainable sphagnum peat moss, go to:
Canadian Sphagnum Peat Moss Association

For more info on global peatland conservation, go to:
International Mire Conservation Group

Guidelines for Global Action Plan for Peatlands

International Peat Society


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