Almost any potted plant you can buy grows in a soil mix that contains peat moss, and most bagged potting soil does, too. You can also buy it on its own to mix into your own potting soil blend. It’s especially useful for growing flowers and food in containers because it helps these thirsty plants get the moisture they need. Despite the fact that this brown, fibrous substance is so common and useful in the gardening world, peat moss has long been a sore point for those in the industry because of its sustainability—or more accurately, the lack thereof. Here's what you need to know about the downsides of peat moss, and what you can use instead.
What is peat moss?
When we’re talking about peat moss for gardening, at least in the US, we’re talking about sphagnum peat moss. Sphagnum is a type of moss that’s most notable for its amazing absorption ability, capable of taking in 20 times as much water by weight as the moss’s dry weight. It’s basically a natural sponge. Sphagnum moss prefers growing in moist tundra-type areas, and most of what gets used for gardening comes from peat bogs in northern Canada. As the sphagnum moss dies in these bogs, it very slowly decays into what becomes the peat moss that's so popular for gardening.
What is it used for?
Potting mix used for container gardening has to be able to drain well to avoid rotting roots, but also has to hold onto enough water so the plants have a chance to get what they need. As a solution to this challenge, “peat moss is a marvelous substance,” says Linda Chalker-Scott, a horticulture professor at Washington State University. She points out that it actually helps with both of these needs, acting like tiny sponges throughout the soil that hold the water and slowly release it as a plant’s roots need it.
Why should you care about peat moss?
Aha, the tricky question. The answer has to do with what happens when it's harvested. Remember, peat moss forms really, really slowly in cold, boggy ecosystems. The peat moss industry harvests less than 2% of the existing supply each year and says that this amount of collection is sufficient to keep up with demand. Even though that doesn't sound like a lot, areas that are harvested can't recover at a fast enough rate for peat moss to be considered a renewable resource.
“We cannot replace the peat biomass that we remove from a bog in a human being’s lifetime,” says Paul Short, the president of the Canadian Sphagnum Peat Moss Association. However, he points out that the CSPMA does engage in aggressive restoration efforts such as reseeding moss from nearby bogs to get the peat formation process going again in harvested locations.
Despite these restoration efforts, peat moss probably can’t be harvested again, in the same quantities from the same bog, for a thousand years or more. “It's almost impossible to get it back to the way it was,” says Chalker-Scott. “I compare it to cutting down old-growth forests. Sure, you can plant new trees, but it's going to take a long time.”
It's almost impossible to get it back to the way it was. I compare it to cutting down old-growth forests. Sure, you can plant new trees, but it's going to take a long time.
Another issue is that peat bogs are the single largest carbon sink on the planet; they store lots and lots of carbon dioxide because of how very slowly decomposition happens. This is important because this is one of the ways the planet naturally helps minimize the greenhouse effect of too much of this gas in the atmosphere. When you remove the peat moss, it releases a lot of stored carbon dioxide and that's bad news for our climate.
What are the alternatives to peat moss?
Chalker-Scott recommends avoiding it completely. “It doesn't do anything that's crucial for plant life,” she says. “Otherwise there wouldn't be any plants except right around peat bogs.” Peat moss makes soil better able to absorb and hold water, but it isn’t required. Given how slowly peat moss forms in nature, collecting it is hard to do in a truly sustainable way—and if you don’t need it, why use it at all?
Luckily, plenty of other options exist. When it comes to bagged potting mixes, you can find ones that don't use peat moss, so check the label before you buy. They may instead contain other plant-based materials such as coconut coir (a fiber extracted from used coconut husks), recycled paper fibers, and compost. You can also try making your own mix from these alternatives.
It’s important to know, though, that none of these materials work quite as well as peat moss. They certainly help, but don't result in such forgiving soil: with peat moss, you can underwater or overwater your plants and they’ll still be fine. With the alternatives, you may need to pay a little more attention when watering. “I think for gardeners there's going to have to be a little experimentation to see what works best for them,” says Chalker-Scott.
If you can't find a peat-free potting mix that you like, you can look for the logo of the CSPMA on bagged mixes. If you see it, you’ll know that at least there has been an attempt to restore harvested bogs. Even if it’ll take hundreds of years for the peat to regrow, the bogs are on their way to becoming functioning ecosystems again, even if they won't ever be identical to the way they were before.
As gardeners, being more mindful of where all our materials come from will help us make a conscious choice about what to use and how much of it. Even though there's no one-size-fits-all solution for avoiding peat moss, there are more sustainable options for providing your potted plants with what they need to thrive.