Is peat moss a sustainable garden amendment? Part 1
Arguably the most important component of building a flourishing garden is ensuring you have healthy soil. Healthy soil provides the necessary nutrients for plants’ growth, provides the right pH, and is light enough to facilitate proper water drainage while also holding moisture and allowing for ample root spreading. With this in mind it’s no surprise most soils need amendments to improve garden performance (healthier plants, greater yields).
One highly popular soil amendment used to improve soil is peat moss. I first read of using peat moss when reading Agricultural Ecology by the late Professor Joy Tivy (wiki bio). Sphagnum peat moss, or plainly known as peat moss, is decomposed sphagnum moss. According to the Canadian Sphagnum Peat Moss Association (CSPMA; see site), peat moss has a large cellular structure which enables it to absorb air and water similar to a sponge. It also prevents nutrient loss (via leaching*) by absorbing them and slowly releasing them over time as plants take up nutrients from the soil, creating a favorable chemical gradient.
However there is an unfortunate downside to using peat moss depending on the source. According to Professor Tivy, who was quite ahead of her time, and Oregon State University Extension Service horticulturist Linda McMahon ,peat moss is unsustainable because it takes hundreds of years to form (see here). Therefore it will not be renewed for hundreds of years after being harvested and shipped out to amend a gardener’s soil. Being an environmentally concerned gardener who also wants great results, I decided to research the issue further.
My first concern was the renewability of peat moss. The CSPMA, which supplies the majority of the peat moss in North America (see here) claims that peat moss regenerates at a rate of 1-2 mm per year. CSPMA also claims that there are about 280 million acres of peat lands in Canada, of which only about 42,000 acres (or 0.02%) are harvested annually for gardening and horticultural type use. If these numbers are indeed true then it would seem Canadian peat moss is a renewable resource. Two caveats here are firstly that Joy Tivy was concerned about peat moss harvested from ancient peat bogs in Scotland**, so the CSPMA’s claims do not apply since Scotland is not Canada. It is not clear if McMahon’s concerns are with peat moss in general or if she makes a distinction between peat moss based on origin (i.e. Canadian versus Scottish).
The second caveat is that in the many articles I have read discussing the supposed sustainability of Canadian peat moss, the source was the CSPMA. Clearly there is a conflict of interest here. That CSPMA espouses the sustainability of their peat moss is analogous to processed food manufacturers claiming that soft drinks and sweets don’t make kids fat. However the claims made by the CSPMA appear to be supported by independent researchers.
In a review paper entitled Threats and protection for peatlands in Eastern Canada published in the French geographical journal Géocarrefour, Poulin et al point out that despite the fact that 7.3 million cubic meters of Canadian derived peat are sold each year, the peat moss industry only affects 42,000 acres of the 280 million acres of peatland in Canada, which supports the claims of the CSPMA (1). In addition, the review notes that the Canadian government and several provinces have adopted policies to ensure protection of Canadian wetlands, and that CSPMA regulates its members by encouraging practices including to:
- utilize exploitation methods that will minimize the affected surface area,
- leave some plots of natural peat as a buffer zone and to stimulate recolonization,
- utilize waste surface vegetation to revegetate recently abandoned sites and...
- apply restoration techniques following exploitation.
Nonetheless the authors conclude that while general wetlands conservation is an integral component in Canadian national and provincial conservation plans, current plans for conservation of peatlands specifically are potentially inadequate (no specifics are given as to why). Apart from serving gardening and horticultural purposes, peatlands have been disturbed for other purposes such constructing hydroelectric dams, reclamation agricultural purposes (such as cranberry production).
So to wrap it up, I’ll say as a cynic I am not completely sold on a self-policing industry association but based off the information I can find, it does appear Canadian peat moss is being harvested at sustainable rates. Other considerations include environmental costs of transporting the peat to various locations around the world. One of my fellow gardeners who I have been sharing this information with asked how to ensure that the peat moss she buys is Canadian or approved via CSPMA. As it turns out CSPMA member companies compose about 95% of Canada's total peat moss harvesting and production according to a recent press release (see here).
In the next post, I will discuss potential peat moss alternatives for those who are not comfortable using it…
*Nutrient leaching refers to the downward movement of nutrients into layers of soil below that of which the roots occupy. The phenomen generally occurs with rain or irrigation. I’ve seen this happen firsthand to gardeners who are overzealous with their watering. Read here for more information on nutrient leaching.
** Inherently all peat bogs are all very old, thus bogs in both Canada and the UK are ancient! I believe Joy Tivy’s concerns had more to do with their being lack of adequate conservation plans in the UK. However a recent report produced by Scotland’s Royal Society for the Protection of Birds (RSPB) led by professor Richard Lindsay highlights the importance of peat bogs including their ability to participate in the carbon cycle (sequester carbon dioxide or release methane) depending on their biological activity and plant matter (see here). The issue is very complex and beyond my grasp as a casual reader however my interpretation is that conservation is most likely a good policy irrespective of the source. I plan to elaborate more in further posts.