Before the mid-1900s, peat moss was largely unavailable and unused by gardeners and farmers in the United States. In the decades since then, peat’s popularity has increased dramatically. And with it, an unanswered question: Is peat moss a responsible and sustainable choice for gardeners?
Peat is the partially decomposed remains of plants, most commonly sphagnum moss. It forms over many millennia in bogs, marshes, and swamps—known as peatlands or peat bogs—often gaining less than a millimeter in depth every year. The process is simple but very slow.
As sphagnum moss grows on the surface of a bog, the older parts of the plant are submerged in oxygen-poor water. The lack of oxygen slows decomposition dramatically, preserving the moss and anything else that falls into the bog. Given enough time, submerged sphagnum moss forms the dense, absorbent material known as peat moss. Left alone, the process won’t stop there. Although the transformation requires eons, undisturbed peat will eventually form coal. Peat is essentially young coal—a baby fossil fuel. And, like all fossil fuels, it is rich in carbon.
A 2009 article in the journal Science makes the claim that, “meter for meter, peatlands store more carbon than any other terrestrial ecosystem.” All told, the world’s peat bogs store approximately 562 billion tons of carbon—more than all the trees in the world, and roughly equivalent to half the carbon currently in the atmosphere as carbon dioxide, or CO2. Healthy peat bogs accumulate an additional 110 million tons of carbon every year, more or less. All this despite the fact that peat bogs cover only 3 percent of Earth’s land and freshwater surface.
When peat is mined, this stored carbon is vulnerable to release into the atmosphere, where it contributes to the problem of global climate change. Whether used as a soil amendment or a fuel source, peat releases its stored carbon when it decays or burns. Additionally, because peatlands must be drained of their water before the peat can be mined, the bogs also release carbon during the mining process. The International Peat Society reports that some mined bogs continue to exhale carbon into the atmosphere long after the completion of mining, often despite habitat-restoration attempts.