When I was a new gardener at Twin Oaks Community in central Virginia, I was a bit surprised to find the crew using peat moss in the potting mix. I come from the UK, where gardeners’ use of peat has long been challenged as unsustainable and ecologically destructive. I lived in Yorkshire and frequently took walks up on the “tops” (moors). I admit it did take me a while to come to appreciate the treeless stark beauty there. The moors are wild, wet and windy. You get wide views (if the mist or rain is not too thick). You get space and isolation, and tons of very fresh air. There are ancient trackways where salt and coffins were carried, and standing stones, and abandoned industrial workings such as millstone carving sites and mines. If you go alone, you need good navigation skills in the less-traveled parts. If you are unwary, you can find yourself thigh-deep in a bog, and the water is never warm.
In previous times, various efforts were made to drain the water and make the land arable or forested. Meanwhile, local people (or at least the “hearth-holders,” and I feel sorry for the others) had Rights of Turbary, meaning that each summer they could cut out slices of peat (turfs or turves) from the section of common or private land they had rights to, dry them and haul them home as winter fuel. More recently, interest rose in preserving the unique moorland ecosystems. The rich had their pheasant shoots, and they still do. The gamekeepers conducted controlled burns of the heather and bracken to make sure the plants grew tender new shoots at the time of year the young pheasants needed them. Sheep had some access. People enjoyed the birdlife, the heather flowers, the carnivorous sundew plants, the cottongrass, the mosses and other bog plants.
There are many types of peat moss, including 160 species of sphagnum moss. It grows slowly, and needs acidic water and cool-to-cold temperatures. It could be a renewable resource in places with very large amounts of untouched peat bogs, like Canada. That is, if we only harvest small amounts. But, oil and coal could theoretically be renewable if we wait long enough! The Canadian horticulture industry does have some guidelines and best management practices and a certification program for Responsibly Managed Peatlands. You can read about them in Jennifer Zurko’s article I describe later. There are some restoration projects, including the Moss Layer Transfer Technique, a kind of grafting or transplant process. The suppliers do have some “enlightened self-interest” in preserving their goose that lays the golden eggs. In 2021 in the UK, a phased-in ban on peat-based growing media will reach a complete ban in 2024. The rate of progress with phasing out sales was seriously set back when lots of new gardeners wanted peat during the Covid pandemic! Most retailers did not start phasing it out! The UK supply of peat is much smaller than in Canada, and the situation there is critical.
Relatively recently, many people have realized the enormous value of peat bogs as a big carbon sink. Keeping carbon in the ground is one way to strive to reduce the impact of climate change. The wet, anaerobic conditions hold the carbon in the dead plant matter. If we burn it, obviously the carbon is released. This is also true if we use peat in our gardens, mixing it with other ingredients and exposing it to the air. Peat is not coal, it’s not yet a fossil fuel, but it’s on its way. If you use peat, you may have noticed the old heather twigs, and leafy and mossy bits.
In a small country like the UK, it’s more obvious that the rate of use of peat exceeds the rate at which it is laid down. The UK is committed to limit or to completely stop peat use in the home garden market in 2024, and in the professional market by 2030. In the US, we import most of our peat moss from Canada, a large country with a relatively small population clustered close to the US border. Who sees the peat bogs? But the environmental impact is the same. Using peat moss contributes to global heating.
We reduced our use of peat moss at Twin Oaks by first discovering that our homemade compost could be screened (sieved) and used alone for potting transplants and sowing seeds in flats. Our remaining use of peat was for soil blocks. Soil blocks are cubes of potting media that can stand alone and grow seedlings. No plastic pots! To work in a soil blocker, the mixture must be quite wet and sticky. We experimented to find a recipe with as much homemade compost and as little peat moss as possible.
Next, we switched to replacing the peat with coir, the fibrous stuff from coconut shells. It is sold in compressed bricks that need soaking in water and crumbling before use. The material has been shredded, and is easy to use. This is a by-product of growing coconuts. No coconuts are harvested just for the coir. It seems like a freebie, a “waste” product. Maybe our purchase helps people in poorer countries to get more money for their agricultural efforts. Of course, getting the coir from the tropical coconut-growing regions does involve some shipping. It’s shelf-stable, so can come by ship, using less fuel than air transportation. However, maybe the coconut groves would benefit from the coir being returned to the soil below the coconut palms. There are no “wastes” in agriculture.
We still use coir for soil blocks, but we reduced our use of soil blocks, and last year made none at all. Now we use Winstrip trays instead of soil blocks. These are heavy-duty plastic with many years (decades?) of use ahead. They have square cells with vertical slits in the sidewalls and a staggered arrangement allowing air to prune the roots of the seedlings, one of the values of soil blocks. With Winstrip trays, we can use 100% home-made compost, not bought-in imports at all. Filling the Winstrips is very quick, much quicker than getting a good block mix and ejecting each set of four soil blocks.
Transplanting from Winstrips is almost as easy as transplanting soil blocks. With soil blocks, you open a hole in the soil (I used to like a right-angled trowel for this job; Eliot Coleman advocates a cut-off bricklaying trowel). Drop the block in the hole and firm the soil back in place. With Winstrips, you poke the plug up through the hole in the bottom, then lift it out, and it’s just like planting a soil block.
Margaret Roach addressed this issue with Brian Jackson, an expert in soil-less growing media on her website A Way to Garden: Can we Replace Peat Moss? You can read the interview or listen to the podcast.
The January 2022 issue of GrowerTalks magazine has an article from an industry perspective: Is Peat Sustainable by Jennifer Zurko. There is an archived version of an earlier webinar, linked from the article, if you prefer that format.
Suppliers of other potting media are selling ground composted bark and rice hulls. The same questions remain. In the case of rice hulls, the additional question is, do we want to aid and abet the eating of hulled white rice? And another is whether the potting mix has any nutrients for the growing plants. If you can make and use your own compost, you can be confident your plants will get nutrients. Commercial potting mixes have nutrients added. Making a change will involve assessing your options and the results you get. Using a different medium will require other changes, like how much you need to water. It will involve paying more attention than you needed for doing the familiar.
So, we are back to using (very durable) plastics and no longer buy any peat moss. Probably we won’t buy coir again either, once we have used what we have in stock. This is one of those agricultural dilemmas everyone gets to find their own solution to. Peat bogs can perhaps be restored eventually, but we need to then leave them be, and leave peat in the ground, as with coal and oil.