Peat moss is the primary ingredient in most bagged potting soil mixes. It’s also used extensively in many custom mixes and can be purchased in dried bales. Peat moss is made from partially composed Sphagnum moss that is harvested from peat bogs. Peat has many highly desirable horticultural qualities. It has a high water-holding capacity, is mostly sterile, and has excellent structure for plant growth. Peat does not possess adequate nutrients naturally to support plant growth, so fertilizers are necessary to feed plants grown in peat-based mixes. Over time, peat becomes increasingly acidic and loses its structure, so it is must be pH balanced before use and componens are usually added to give the peat structure.
There is considerable controversy over the ecological impact of peat harvesting. Most of the world’s peat is harvested from peat bogs in Canada and to a lesser extent, Europe. Because Sphagnum moss grows very slowly, there are environmental concerns associated with harvesting peat at an unsustainable rate. In Great Britain, scientists have documented long-term damage to the country’s peat bogs. However, newer techniques, such as “slicing” the top layer of Sphagnum moss and leaving lower levels to regrow, are sustainable. The Canadian Sphagnum Peat Moss Association estimates that less than 1 percent of the country’s available peat bogs are being harvested.