Is Peat Moss Sterile?

Peat moss is a more complicated topic than is generally considered. Its composition varies from place to place, and harvesting methods play a big role in its sustainability. Most peat moss is not sterilized, but it is essentially free of harmful elements, such as insects or pathogens, and even contains beneficial microorganisms. You have a lot of variables to consider for such a simple product.

Peat moss is different from country to country because of the way it forms. Peat bogs are saturated with water and stagnant, which produces an environment that is poor in oxygen. Because many soil microbes need oxygen to survive, peat bogs have only low levels of soil microbes, and the dead plant matter that accumulates breaks down very slowly. This partially decomposed plant matter is peat moss. However, what type of plant matter it is varies depending on the region and what types of plants grow in it.

Canadian sphagnum peat moss is one of the most commonly used types of peat moss and has a number of advantages. It is harvested sustainably, and studies have found that sphagnum peat moss contains beneficial microbes. These microbes, able to survive the low oxygen environment of the bog, include Penicillium, Streptomyces, Arthrobacter and Trichoderma and can benefit the plants for which the moss is used. However, different types of peat moss have different levels of protection. The older the peat moss gets and the more decomposition it sustains before harvesting, the less disease suppressant properties it will have. Lighter "blonde," fibrous peat moss, harvested from the surface of the bog, is the only kind that retains the amount of microorganism necessary to inhibit diseases and that lasts for around 6 to 10 weeks.

Peat moss is used in gardens to amend soils, provide aeration and create good drainage. It’s an ingredient in many potting soils and mixes and a carbon source for composters. It is sometimes used as a surface mulch, but this is its best use. Peat moss pulls water away from plants and can be used to create good drainage if mixed into soil, but as mulch it dries out and begins to repel water. It doesn’t bring a lot of nutrients to bear, but it is good for growing mixes when you’re starting seeds or cuttings.

Most companies neither sterilize nor pasteurize peat moss. Not only is sterilization an expensive process, but sterilizing would eliminate the beneficial microorganisms that inhibit some diseases. However, because of the environment from which it comes, peat moss is largely free of pests and diseases.