Since the 1950s, sphagnum peat moss has been a common ingredient in potting soils sold in the United States. It is typically mixed with white specks of perlite, a mineral that is expanded by heating. (Wendy Galietta/The Washington Post)
Gardening columnist

Each year, professional plant growers and hobby gardeners alike go through vast quantities of commercial soil products for seed starting, container gardening, patching lawns and improving growing beds.

In 2006, Mark Highland launched a business to make, blend and sell all those concoctions, but with one key difference. His mixes would not contain the ubiquitous ingredient in most bagged growing media: peat moss.

Virtually all of the peat moss sold in the United States comes from the vast sphagnum moss bogs of Canada. Often mixed with a mineral named perlite, it is highly valued by horticulturists for its ability to retain moisture and oxygen without becoming waterlogged or heavy. It is generally sterile and naturally suppresses a fungal disease that can afflict seedlings, making it a natural choice for seed starting.

So why would Highland, owner of Organic Mechanics in Modena, Pa., go to considerable trouble to avoid it?

Peatlands store a third of the world’s soil carbon, and their harvesting and use releases carbon dioxide, the major greenhouse gas driving climate change. The biggest environmental risk from peatlands is if they catch fire, which happened spectacularly in 2015 in Indonesia on land cleared for plantations. Peatland fires account for up to 5 percent of human-caused carbon emissions, according to the United Nations, which last year launched a peatlands conservation initiative.

Concerns for peat bogs have led to the creation of alternatives using compost, pine bark and coconut fiber. From left: peat moss, Organic Mechanics Planting Mix Compost Blend, Organic Mechanics Premium Blend Potting Soil, PittMoss Prime cellulosic fibers and Organic Mechanics rice hulls. The hulls are a substitute for perlite. (Wendy Galietta/The Washington Post)

For horticultural use, the extraction of peat requires the removal of a bog’s living surface to reach the partially decomposed layers beneath. It grows at a mere sixteenth of an inch a year, and its mining removes layers that take centuries to develop. “Peat is the best vegetative carbon sink we have on the planet,” Highland said. “Why dig it up?”

Highland developed peat-free mixes for seed starting, containers and general soil amendment, and he thought sales would “go through the roof” as gardeners around the world began to equate peat moss use with global warming.

In Britain, for example, using peat has become taboo. The government’s environmental agency has said it wanted to phase out peat moss for hobby gardeners by 2020 and commercially by 2030. The London-based Royal Horticultural Society, the largest gardening organization of its kind in the world, has reduced peat use by 97 percent at its four major gardens and urges its members to follow its lead.

Highland, whose products are carried by Whole Foods Market, says he has seen steady growth in the past decade but not the explosive growth he and others had expected. On this side of the Atlantic, the ecological arguments against peat moss have been far more muted. Whatever the reasons, the issue has not seeped into most consumers’ consciousness.

“I think the average gardener has no idea what peat moss is, where it comes from and whether they should even consider an alternative,” Highland said.

Of the hot-button issues seen by Sally McCabe, who manages educational issues for the Pennsylvania Horticultural Society, peat moss concerns pale next to others. “The biggest is probably Roundup,” she said, referring to the controversial herbicide. She counsels members to minimize peat moss use. “I always push the renewable stuff, particularly locally sourced,” she said.

Canadian peat producers say that the mining is sustainable and that harvested bogs are returned to living sphagnum moss peatland after five years. (Quebec Peat Moss Producers Association)

In northern Europe, dried peat has been used for centuries as fuel — raising its profile as a source of atmospheric carbon dioxide — and people live closer to ancient bogland that has been drained for agriculture and development. In Canada, by contrast, peat isn’t used as a fuel, and its sheer acreage in less populated areas works in favor of its mining. Canada is the second-largest country on Earth and has 25 percent of the globe’s peatlands. The bogs are drained before harvesting, and the top layers of peat are mined with a large vacuum apparatus.

Peat producers make a persuasive argument that they are harvesting sustainably. (Canadian environmental groups I contacted had no position on peat moss.)

The Canadian Sphagnum Peat Moss Association, representing 14 major producers, says that the industry has harvested approximately 73,000 acres out of 280 million acres of the country’s peatlands and that the amount taken each year is a fraction of the quantity that is naturally generated in undisturbed bogs.

Paul Short, the group’s president, said that for the past 10 years, producers have been restoring harvested bogs by allowing them to re-flood and seeding them with shredded moss grafts that grow and knit together. The moss covers the harvest site within five years, he said, and the bog is “back to a near-natural condition within 10 to 15 years,” he said.

The argument is convincing to horticultural growing media producers such as Karl Hammer, who uses Canadian peat moss in the mixes he makes for commercial greenhouse growers and others. “Obviously, it’s a resource that has to be used respectfully, but I don’t see it going away,” said Hammer, president of Vermont Compost Co. “We should focus on using less gasoline, not less peat.”

Highland is unswayed. “There are many ways to argue what’s sustainable,” he said. “Any forest is sustainable if you plant more trees,” but the original old growth trees are gone, he said. A mined peat bog “is never going to return to its former self,” he said.

If you believe that using less peat is a good thing, you may want to reserve your peat consumption to container use and seed starting rather than the soil amendment and lawn work, which consumes larger quantities. Because of its low pH, peat is still a go-to amendment when planting acid-loving plants such as heathers, azaleas, blueberries and pieris.

For general soil improvement, I use mixtures of compost and leaf mold, either homemade or commercially produced. This meshes with the Royal Horticultural Society’s advice. “We believe that using peat for soil incorporation and ground mulching is unnecessary and unacceptable,” spokesman Garfield Myrie wrote in response to an email.

Peat alternatives

As a growing mix, peat doesn’t need a lot of company. Pure, compressed bales of sphagnum peat moss are sold to consumers, but in mixtures for containers and seed starting, peat moss is generally blended with inert minerals to improve its moisture- and nutrient-holding qualities: perlite, a volcanic glass, or vermiculite, a mica. Both are expanded by high heat. Typically, lime is added as well to raise the pH. One drawback is that if peat is allowed to dry out, it shrinks and is difficult to re-wet.

Alternatives to peat tend to be more heavily blended with one another to achieve peat moss’s desired qualities.

Compost: Compost is made from rotted plants, green waste and animal manures. It is inherently renewable, and making your own is cheap and minimizes your carbon footprint (no shipping). The rub is that compost takes time and skill. Authentic compost is a careful blend of nitrogen and carbon sources, turned frequently, kept moist but not wet, and screened for use — all reasons to buy high-quality bagged compost. Most backyard compost piles are merely aging piles of organic matter that don’t get hot enough to kill weed seeds or pathogens.

Coconut fiber: Coconut fiber, called coir, is a byproduct of fiber processing and has become a favored alternative to peat moss over the past 20 years. India, Sri Lanka and Vietnam are centers of production. It has the same water holding and porosity of peat moss, though it is generally used as one ingredient in a mix.

Its distant origins raise questions about the carbon footprint of its shipment to the United States. In addition, it derives from coconut plantations that may have been carved out of rain forests, Short said. “Yes, it’s a byproduct, but this isn’t Tom Hanks wandering around an island picking up coconuts,” he said. “These are plantations.”

Pine bark: Finely shredded and composted pine bark (not pine nuggets, pine needles or pine mulch) is a valuable substitute for peat moss as part of a mixture.

PittMoss: PittMoss was created by an inventor in Pittsburgh and consists of reconstituted paper fibers with added proprietary ingredients. It can be used alone or mixed with potting mix, based on the product used.

Rice hulls: Sterilized rice hulls are not a substitute for peat moss but replace perlite and vermiculite, the production of which requires fossil fuels.

Worm castings: This is the waste from farmed earthworms, rich in nutrients and beneficial microbes, and used as a common ingredient in peat-free mixes.

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