If you are a gardener who will either purchase a plant in a container this year or pot up annuals to place on your patio, chances are you’ll find peat in the planting mix. Peat is used for its water-holding capacity (20 to 25 times its dry weight), ability to hold and supply nutrients to the plants and to provide oxygen to the roots.
Historically, it was used for insulation in homes in arctic regions, for fuel, especially in the UK, and as a wound dressing in the first world war.
Peat is dried, decayed moss, primarily Sphagnum moss in the northern hemisphere, where most of the world’s peat supply exists. Peat bogs also occur in southern Chile, Argentina, New Zealand and Tasmania. About 3% of the earth’s land surface is a peat bog ecosystem.
As the Sphagnum and other mosses die, they sink and gradually decompose in the anaerobic, water saturated environment, accumulating at the rate of about 1/32 of an inch per year. It can take 1,000 years for just 3 feet of peat to form. Over many millennia, peat bogs have reached depths of up to 50 feet.
Peat accumulation provides habitat for a wide array of unique plants, including sedges, ericaceous shrubs, such as azaleas (Rhododendron sp.) and bog rosemary (Andromeda polifolia), orchids, and carnivorous plants of the genus Drosera, commonly called butterworts.
The UK has lost about 95% of its peat bogs in the last 100 years, burning most of it for fuel. A ban on the sale of peat-based products was to go into effect in 2024, but government officials recently pushed that back to 2030, disappointing environmentalists who are concerned about the plants and animals that rely on that environment.
Most U.S. peat comes from Canada, which has about 25% of the world’s peat supply. Despite the vast supply, 80% of Canadian peat producers have adopted best management practices and restoration techniques.
To harvest peat, the living surface plants are first skimmed off, the wetland is drained and then thin layers of peat are vacuumed up. After harvesting is complete, the peatland is re-flooded and recovered with a 3-inch layer of moss seeds, rhizomes and spores removed from unaltered peatland. The Canadian Sphagnum Peat Moss Association claims that restored sites will recover to their original form within 10 to 20 years.
Peat does have problems as a soil amendment. When used in containers, it needs to be lightened with products such as perlite to increase aeration. As a garden soil amendment, it breaks down quickly, reducing soil oxygen. It also has acidifying properties in the soil.
Though some people use it as a surface mulch to lessen weed emergence, this practice is not recommended, for dried peat repels water, reducing percolation and increasing runoff. Harvesting and removal of peat is also responsible for almost 5% of global carbon dioxide emissions, thus exacerbating global warming.
It is highly unlikely that peat will be removed as a horticultural product anytime soon, but there are alternatives that will decrease the supply needed for the industry. One that you may see included in your bag of potting mix is coir (pronounced koi’er), which comes from the pith of a coconut husk.
Coir holds about 10 times its weight in water, not up to the capacity of peat, but adequate to promote aeration and root growth in most potting mixes and lasts longer before breaking down. It also utilizes a material that would otherwise be considered a waste product.
Wood fiber is also used in potting mixes. It is lightweight, provides good soil structure, good drainage, and is inexpensive, since it may be locally sourced. Shredded wood chips, which are available just about anywhere, can also be used. I once knew a nurseryman who used nothing but composted wood chips for container plant production. It took some experimentation to figure out the watering and fertilizing regimes, since it did not have the water or nutrient-holding capacity of peat, but it eventually worked just fine. Homeowners can utilize this system by screening out the larger chips and adding the fines to their potting mixes.
Peat is considered a renewable resource, but it is currently being used at a faster rate than it is regenerating. Eventually, the supply, and plants which depend on peat bogs for habitat will reach critical levels. Gardeners can do their part by reducing the amount of peat that they use and look for products containing coir and wood fibers.
As Helmut Sihler of Norway once said, "The environment is too important to be left solely to the environmentalists." We all need to be environmentalists.
Cedarburg resident Glenn Herold was professor of horticulture at Illinois Central College, East Peoria, Ill. from 1979 to 2011. He earned his BS in biology and MS in horticulture from the University of Wisconsin-Madison. Currently he holds memberships in the Midwest Regional Hosta Society, American Hosta Society, American Conifer Society, The Maple Society, Wisconsin Woody Plant Society, and Wisconsin Hardy Plant Society. Anyone with questions or comments, can email Glenn at PlantmanGlenn@gmail.com.
Additional articles on plants and gardening can be found on his blog:
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