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.

In the United States virtually all of the peat moss sold 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, Pennsylvania, 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 per cent of human-caused carbon emissions, according to the United Nations, which last year launched a peatlands conservation initiative.

Living surface

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 says. "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 organisation of its kind in the world, has reduced peat use by 97 per cent 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 says.

Controversial herbicide

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 says, referring to the controversial herbicide. She counsels members to minimise peat moss use. "I always push the renewable stuff, particularly locally sourced," she said.

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 favour of its mining. Canada is the second-largest country on Earth and has 25 per cent 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 about 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, says 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 says, and the bog is "back to a near-natural condition within 10 to 15 years".

Acid-loving plants

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," says 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 says. "Any forest is sustainable if you plant more trees," but the original old-growth trees are gone. A mined peat bog "is never going to return to its former self".

If you're a gardener and 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. But peat? It's a no go. This meshes with advice from Britain's Royal Horticultural Society. "We believe that using peat for soil incorporation and ground mulching is unnecessary and unacceptable," spokesman Garfield Myrie says.

The Washington Post