Should We Stop Using Peat?

A lot of peat is used in horticulture — as a soil amendment, in lawn patching, in seed starting, and in container gardening — but there’s a growing controversy about it.  I just checked my bag of potting soil, and sure enough, a primary ingredient was peat.  It’s all-natural and naturally organic, so what’s the problem?

It took a bit of digging (no pun intended) to fully understand the issue.  First, let’s be clear on terms, of which I was woefully ignorant. Peat is the decomposed remains of moss from bogs; strictly speaking, it’s not the growing moss itself. Peat is found underneath the growing moss, and this peat layer often goes very deep — several meters typically — and is of ancient provenance. Its use in horticulture began in the 1940s and 50s, and its air- and moisture-holding capacity makes it a highly effective growing medium for commercial producers and a very popular component of potting soil for home gardeners.

 

Where does peat come from?  Peat comes from peat bogs, which are often referred to as peatlands.  Peatlands are unique ecosystems that are rare on earth, covering only 3% of the Earth’s surface.  Some peatlands are found in Asia and in northern Europe, but in these regions, much of the peatland has been exploited and degraded due to human activities, including the use of peat for fuel, and more recently, due to fire.  Most of the remaining unspoiled peatlands are in Canada, though there are a few in the northern United States.  For us American gardeners, a key fact is that virtually all of the peat moss sold in the United States comes from the vast sphagnum moss bogs of Canada. Peat producers harvest the peat by first draining the bog and then extracting the peat with vacuuming machines. This extraction process is the heart of the problem.  Why?  Because peat is very rich in carbon.

Remember that the plant carbon cycle involves both storing and emitting carbon; i.e., plants remove carbon from the atmosphere for photosynthesis, and the carbon is eventually released by decomposition after a plant dies.   As plants remove carbon dioxide from the atmosphere, they store it as carbon in leaves, stems, branches and roots.  This is why trees are major carbon storage facilities. But there’s another major carbon sink — yes, that’s it — peat bogs.  There’s something special about the cold, wet, anaerobic conditions in a peat bog that promotes rapid carbon fixation, with little being released into the atmosphere.  Although peatlands cover only 3% of the Earth’s surface, they store an estimated 15%–30% of terrestrial carbon.  In our current climate crisis, we need to keep that carbon sequestered, but unfortunately, the extraction of peat for horticulture releases carbon. In fact, most disturbances in peat bogs —  whether in the form of wildfires, permafrost thaw, or human disturbances like drainage and extraction —  release carbon to the atmosphere.  The possibility of such carbon releases is why the recent discovery of a vast peatland  in Africa has set off alarms.  See “The Race to Defuse Congo’s Carbon Bomb.”

It’s no surprise then that peat bogs have recently garnered much attention from scientists and environmentalists. Measuring the precise amount of carbon stored in Earth’s peatlands is an ongoing project, and scientists are also urgently measuring how much carbon is being emitted when peat is disturbed or warmed by recent heat extremes.  We are all relying on Earth’s natural carbon sinks to help us mitigate climate change and to meet the greenhouse gas reductions required to achieve net zero by 2050.  Reducing emissions from industry, automobiles, and the like will not be sufficient, so maintaining natural carbon sinks like the peatlands becomes very important.  It must be noted that the estimated total emissions resulting from peat “harvesting” only contribute a small percentage of the carbon emissions attributed to peat “disturbance.”  The heavy hitters are road and mine construction.  “Natural Climate Solutions for Canada,” Science Advances (2021).

If peat mining is a small percentage of the total emissions, do we really need to worry about it? Avoiding the use of peat in horticulture will definitely help preserve the carbon stores in peatlands, although there are those who disagree. But besides carbon-storing, there are other important benefits to the unique ecology of peatlands; the Canadian peatlands hold a large volume of freshwater that supports many rivers, lakes, and other wetlands. This freshwater is critical for the diverse plant and animal species in peatlands, including some highly specialized plant species that are adapted to wet conditions.

Most Canadian peat producers revegetate the bogs, and scientists have studied these efforts.  It so far appears that these restoration programs are somewhat helpful, though it takes a long time for the peat bogs to return to normal:

 “Long-term studies of horticultural peat extraction sites suggest careful restoration can shift these peatlands from C sources back to C sinks within two decades. However, the portion of peat C lost during extraction (typically the top 1 m or greater) and drainage is much greater than the peat C that may be recovered within 20 years of restoration.”

–Frontiers in Ecology and the Environment Reviews: The essential carbon service provided by northern peatlands,” Frontiers in Ecology and the Environment, Ecological Society of America Journals/WileyOnline  Harris et al, November 2021 https://doi.org/10.1002/fee.2437

What are the Alternatives to Peat?

If I decide to avoid using peat, I’ll need an alternative, especially for potting soil.  There are definitely alternatives to peat, but there may be problems with some of them.  The possible substitutes, according to one expert, are wide-ranging:

“International research on peat alternatives dates back at least 30 years and has identified a plethora of materials whose easy availability, low cost, and sustainability make them attractive substitutes for peat moss. These materials, alone or in combination, ranging from traditional materials such as composted bark, yard and agricultural wastes, and livestock manures to more current waste products including brewing waste, coconut coir, olive mill waste, pulp and paper sludge, municipal solid waste and sewage sludge, and even foam cubes. These materials have been used in the rooting and/or production of many plant materials, including vegetables, annual flowers, houseplants, woody ornamentals, and timber species.”

–Linda Chalker-Scott, Washington State University.

Coconut coir is probably the most popular and likely to succeed as a replacement, though its transportation from Southeast Asia will undoubtedly involve green house gas emissions.   Because Britain has been reducing peat use for some time now, its work on peat alternatives is worth a look.  The Royal Horticultural Society has helpful advice on its website, Peat-Free Growing Media/RHS.  There are peat-free potting soils on the market, though they are more expensive.  You can make your own, using recipes at No-Peat Potting Soil Options/University of Minnesota Extension.

Now that I’ve looked at this issue, I’ll probably never indiscriminately grab a bag of potting soil again.  I’ll be that person hunched over the bag and reading the label, and that’s a good thing. Oh, and one more thing, now that I know how rare they are, I’d really like to visit a peat bog some day.

 

SOURCES:

Featured Photo:  Sphagnum capillifolium, Photo by Rob Routledge, Sault College, bugwood.org

“Is this popular gardening material bad for the planet?”  Washington Post (2017)

“Monty Don urges gardeners to stop using peat compost – and faces a backlash: Gardeners should avoid plants grown in peat and peat-based potting compost, says the broadcaster,” Real Gardens (2020)

“Ken Druse:  The Real Dirt on Peat Moss,” GardenRant (2009)

“The essential carbon service provided by northern peatlands,” Frontiers in Ecology and the Environment, Ecological Society of America Journals (Harris et al, 2021)

Global Biogeochemical Cycles (2008) (Peat is very rich in carbon because “carbon fixation occurs at a more rapid rate than decomposition under the cold, wet, anaerobic conditions within northern peatlands, so that organic matter accumulates.” Thus,”peatlands serve as large repositories of stored carbon, an amount representing 25–50% of current levels of atmospheric CO2.”)

Colorado State University Extension/Choosing a Soil Amendment (the peat harvest rate greatly exceeds the vegetation rate of the Canadian peat bogs, so it is considered only a semi-renewable resource).

Bowdoin.edu/news/2017/Peat Bogs May Contain Important Climate Change Indicators

Radiocarbon Analyses Quantify Peat Carbon Losses With Increasing Temperature in a Whole Ecosystem Warming Experiment (Because cold temperatures are believed to contribute to the slow decomposition of peat C, climate warming could accelerate C losses in the form of carbon dioxide (CO2) and methane (CH4), which are two important greenhouse gases.)

“Prompt active restoration of peatlands substantially reduces climate impact,” Environmental Research Letters (2019)

“Uncovering the power of peatlands in Canada’s fight against climate change: Waterloo’s Maria Strack explores peatlands as a nature-based solution for carbon sequestration,” University of Waterloo Climate Center.ca

“Northern Peatlands in Canada: An Enormous Carbon Storehouse,” Wildlife Conservation Society Canada (“When peatlands are disturbed, due to wildfires, permafrost thaw, or direct human disturbances (e.g. drainage, peat extraction), more carbon can be released and in a much shorter amount of time. This can turn the peatland into a source of carbon to the atmosphere and contribute to the problem of greenhouse gases.”)

“Reducing the carbon footprint of Canadian peat extraction and restoration,” Pubmed.gov/Ambio (2009)

“Inside the search for Africa’s carbon time bomb: Journey into the wilds of the Congo rain forest with scientists trying to locate a shockingly large peatland so that they can help to preserve it,”  National Geographic.com