Peat Moss as a Fertilizer

Peat moss is highly valued as a fertilizer, soil conditioner, seed starter medium and compost additive because of it acts like a sponge, absorbing as much as 16 times its weight in water. It holds moisture and soluble fertilizers until it is saturated, then starts a measured release of liquid to surrounding soil and plants. Most North American supplies are from Canadian sphagnum peat moss (Sphagnum cymbilifolium) bogs.

As a fertilizer, peat moss makes soils more fertile by loosening up clay soils for better root aeration and helping sandy soils retain moisture and nutrients. The natural acidity of peat moss (pH of 3.4 to 4.8) lowers the pH of neutral and alkaline soils, providing a better growing environment for most vegetables. For acid-loving plants such as blueberries, peat moss is a natural, organic growing medium amendment that helps berries thrive. Peat moss does not supply nutrients traditionally found in compost, manures or manufactured fertilizers providing a standardized mix of chemicals.

The high acidity of peat moss limits the number of things that can thrive in a peat bog, much less survive. Because of the nature of the bog and harvesting methods used to make dried peat moss, the finished product is essentially free of insects, weeds, salts, and other seeds. These attributes make it a favorite component of seedling mixes and soilless growing media.

A common misconception about peat moss is that sphagnum moss and sphagnum peat moss are the same product. Sphagnum moss is the living moss that grows on top of a peat bog. Sphagnum peat moss is the dead material below the living sphagnum moss. In the manufacturing process, live sphagnum moss is removed so only sphagnum peat moss is harvested. The distinction is important because samples of living sphagnum moss have been found to carry a fungus that can cause a chronic infection that causes skin lesions known as grse gardener's disease. Dead sphagnum peat moss has not been shown to carry the fungus.

According to the Canadian Sphagnum Peat Moss Association (CSPMA), industry processes and practices make harvesting peat a sustainable and renewable industry in Canada. The association points out that Canada has 270 million acres of peat bogs, and the industry harvests on only 40,000 acres. As noted by the CSPMA, regrowth rates are also good in certain bogs, with more than a foot of new growth within 10 to 15 years of a harvest. Across the Atlantic, however, the United Kingdom's Environment and Heritage Service states flatly, "Peat milling is unsustainable, destroying the biological, archeological, and landscape value of peatland." While Canadian growth rates are almost an inch a year, the British bogs see annual removal rates of 200mm and annual growth rates of 1mm, a 200-year renewal cycle.

Because of the unsustainable nature of peat harvesting in the United Kingdom, gardeners there have switched some peat moss purchases to other substances, such as cocoa shells, wood bark and garden mulch. None of these items have the absorption property of peat moss. The net effect is that the amount of peat use has not declined, but the growth rate of peat use has slowed to a fairly constant rate.