What You Need to Know About Peat Moss

Every year, gardeners across Canada flock to stores to buy the perfect ingredients for growing their plants. We search for compost and manure, imagining immaculate gardens and green lawns. This year, however, let your imagination travel instead to un-manicured swampy wetlands and frozen tundra. Here you will find peatlands, a resource as fragile and essential as the rainforests. Although milled peat is great for our plants, it is also important to consider the impact on peatlands.

While most soils are made primarily of weathered rocks or old sediments (minerals), peat soils consist mostly of partially decomposed plants (organic matter). Peat is found in classes of wetlands called peatlands (aka mires, moors, muskeg, or bogs and fens). Although found in many places worldwide, the vast majority of peatlands are in mid (boreal) to high northern latitudes (although about one-quarter are found in the humid tropics). In fact, nearly half of all peatlands on Earth are in permafrost-affected environments where only the surface layer of soil thaws in the summer and deeper soil remains frozen year-round. Unlike nearly all other ecosystems, peatlands are notable for being “out of balance” in inputs and outputs.  Although some processes are slow, like plant growth and breathing in carbon dioxide from the atmosphere, the breakdown of dead plants remains even slower. The unique soil environments in peatlands result in the buildup of organic soils over thousands of years that can be tens of meters deep!

Although containing very few nutrients, peat is often used as a gardening and potting material because it is lightweight, has great water-holding capacity, and provides large air-filled pores. The bulk of peat moss sold commercially in North America comes from Canadian peatlands dominated by Sphagnum moss (mainly bogs). Most commercial potting soils contain peat these days.

However, peatlands are ecosystems far more powerful than just the horticultural benefits of extracted peat moss (the common term for peat soil). Peatlands are homes to rare plants and animals. They also act as Earth’s water purifiers, contributing to healthy watersheds and safe drinking water. It is estimated that peatlands filter 10% of global freshwater resources. Intact peatlands also literally serve as sponges during storm events and prevent damage to homes and other infrastructure.

As well, peatlands are one of the most efficient carbon sinks on the planet. Although peatlands cover only 3% of the planet’s surface, they have stored a third of the world’s carbon since the end of the last glacial epoch. Soil scientists have found that northern peatlands store around 415 gigatonnes of carbon. That is roughly equivalent to 46 years of current global carbon dioxide emissions. It is important to note that the vast majority of Canada’s peatlands are not subject to harvesting. Instead, most face climate change as the biggest driver of potential loss.

Extracting peat involves digging drainage systems and stripping a wetland of its living surface. After draining the wetlands and drying the surface, heavy harvesting equipment compacts any abandoned underlying soil while collecting the top layer. Some of the immediate consequences of peat extraction include the release of stored greenhouse gases and loss of natural biodiversity. 

Abandoning peatlands after extraction is simply not an option. It can take thousands of years for peatlands to develop 2 metres of soil (the average depth of the boreal peatlands). After harvesting peatlands for gardening materials, the leftover peat is unable to support the return of natural plants, like Sphagnum moss. Man-made drainage ditches and the absence of surface vegetation drastically change water flow. The exposed peatland soils are subject to wind and water erosion, and the constant freezing and thawing of the unprotected soil leads to frost heaving. Where these soils were once powerful carbon sinks, milled peatlands experience higher decomposition and oxidation, ultimately becoming a carbon source to the atmosphere.

Research collaborations with the peat extraction sector in Canada have made important gains in our ability to redirect post-extracted peatlands towards reclamation, but challenges remain. Conditions can include thin peat moss, highly compacted soil, and water levels that are difficult to manage (too dry or too wet – often in the same site). It is easy to argue that ongoing research efforts, with the proper treatment, can create relatively natural vegetation cover. However, true “restoration” is not possible in a human lifespan because of the slow rate of soil formation, and some counter that peat should therefore be classified as a non-renewable resource.

Peat is a great medium for horticultural plants, and the peat extraction sector is an important employer in regions of New Brunswick, Quebec, Manitoba, and Alberta. We need to be honest about peat being a non-renewable resource, and if we choose to use it, use it sparingly and look for other more sustainable replacement options.  Let’s turn our attention as soil enthusiasts to protecting this resource and finding other suitable alternatives. The best place for peat is exactly where it came from.

Alternatives to Peat

What can you use instead?

Compost: If you are looking for a sign to start that kitchen compost, this is it. Rotted plants, green waste, and animal manures are a renewable, cheap, and easy to make resource. Compost improves drainage, attracts earthworms, and provides nutrients to your garden. The Compost Council of Canada has helpful tips on how and what to compost on their website.

Coconut fiber: Coconut fiber, or coir, used in gardening comes from short fibers that are leftover after coconuts are harvested. It also has a pH level of 6.0, which is optimal for most garden plants.

Woody materials: Woody materials, such as shredded bark or sawdust, can be used in place of peat. Aim to use by-products of locally sourced wood. Beware of woody products harvested from trees specifically for horticultural uses or those that may be chemically processed.

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