The terms “peat” and “peat moss” are often used interchangeably in gardening, leading to confusion about the material being purchased. This overlap in terminology stems from the fact that one substance is the direct source material for the other, representing different stages of the same biological process. While both are organic materials harvested from wetland ecosystems called bogs, they are fundamentally distinct in their composition and age. Understanding the difference requires looking at the living plant material and the geological transformation it undergoes.
Sphagnum Moss: The Living Source
Peat moss, as it is most accurately known in commercial gardening, is the product derived from the genus Sphagnum, a pale-colored moss that forms dense mats on the surface of bogs. This living Sphagnum moss is the top layer of the plant. It possesses a remarkable cellular structure composed of large, dead cells that can absorb and hold a substantial volume of water, retaining many times its dry weight in moisture. The living Sphagnum moss also actively secretes hydrogen ions, which creates the highly acidic environment that characterizes a peat bog. This acidity slows the rate of decomposition, allowing the plant material to accumulate rather than fully rot away.
The Geological Process of Peat Formation
The actual material known as peat is the result of an extremely slow geological process involving the accumulation of this plant matter. When the Sphagnum moss at the surface dies, it sinks beneath the water table, entering an environment that is low in oxygen. This oxygen-poor, or anaerobic, condition prevents the activity of most decomposition microbes, effectively halting the normal decay process. Instead of fully rotting, the plant matter partially decomposes and becomes compressed by the weight of the layers above it over thousands of years. The dark, dense, fibrous material that results from this long-term preservation is what is correctly termed peat, a highly stable form of organic carbon.
Practical Uses in Gardening
Peat is valued in gardening and horticulture due to the physical and chemical properties it acquires during its formation. The compressed material is lightweight and maintains a high porosity, which improves the structure of heavy, compacted soils by allowing for better aeration. Peat’s fibrous structure allows it to absorb and hold water exceptionally well, potentially holding up to 20 times its dry weight, which helps maintain consistent moisture levels for plant roots. Its high acidity, with a typical pH ranging between 3.5 and 5.5, makes peat an ideal soil amendment for acid-loving plants, such as rhododendrons, azaleas, camellias, and blueberries.
Sustainability and Substitutes
The immense time required for peat formation is the central issue regarding its sustainability as a commercial product. Because it takes thousands of years to create the deep deposits found in bogs, peat is considered a non-renewable resource on any human timescale. Harvesting peat involves draining and mining the peatlands, a process that disrupts the delicate bog ecosystem and releases large amounts of stored carbon into the atmosphere. These peatlands serve as significant global carbon sinks, and their disruption contributes to environmental change. Consequently, many gardeners and commercial growers are turning to alternatives that offer similar benefits without the ecological cost.
Common substitutes include:
- Coir, which is a fibrous product made from the husk of coconuts.
- Composted wood products.
- Pine bark fines.
- Municipal compost.
Coir, for instance, provides excellent water retention and aeration, often performing on par with peat, while being a rapidly renewable byproduct of the coconut industry.