The terms “sphagnum moss” and “peat moss” often cause confusion, leading many people to believe the materials are interchangeable. While they originate from the same plant, the genus Sphagnum, they represent two distinct forms. Understanding this difference is important because each material possesses unique physical and chemical characteristics that dictate its specific use in gardening and horticulture. The distinction lies in whether the material is the fibrous top layer of the bog or the highly decomposed matter deep beneath the surface.
Sphagnum Moss The Plant and Its Harvested Form
Sphagnum is the scientific name for a genus of over 380 species of mosses that grow in dense mats on the surface of wetlands and bogs. When sold commercially as “sphagnum moss,” it is the whole, long-fibered plant that has been harvested, dried, and often compressed. This material is recognizable by its light, spongy texture, retaining the identifiable structure of the plant, often appearing in shades of pale green, tan, or brown.
This dried moss is valued for its ability to hold a large volume of water while allowing significant air circulation around plant roots. Unique hyaline cells can absorb up to 20 times the moss’s dry weight in water. The fibrous strands provide a coarse, open medium that resists collapsing, making it excellent for applications requiring a sterile, moisture-retentive, and airy environment.
Peat Moss The End Result of Decomposition
Peat moss, often called sphagnum peat moss, is formed far below the living moss layer in waterlogged environments known as peatlands or bogs. This material is the accumulation of dead Sphagnum moss and other organic matter that has undergone slow, anaerobic decomposition. Water saturation and lack of oxygen prevent the material from fully decaying, a process that can take a thousand years to create just a few feet of depth.
The resulting material is a fine, dark, homogenous substance that bears little resemblance to the fibrous plant from which it came. This slow decay is aided by the plant’s natural acidity and the secretion of tannins, creating a highly acidic environment with a pH typically ranging from 3.0 to 4.5. When dried, peat moss is compressed into dense bales, and its fine texture allows it to retain a massive amount of water, though it can become compacted if over-saturated.
Contrasting Properties and Usage in Horticulture
The physical and chemical differences between the two forms dictate their specific roles in gardening. Sphagnum moss is characterized by its long, intact fibers and relatively neutral or slightly acidic pH. This makes it ideal for lining wire hanging baskets or serving as a clean, aerated medium for cultivating orchids and propagating cuttings. Its coarse texture ensures ample airflow, reducing the risk of root rot.
In contrast, peat moss is a fine-textured soil amendment with high acidity. It is used to alter the composition of potting mixes or garden soil by improving water retention in sandy soils and helping to break up dense clay. Gardeners leverage its low pH to create optimal conditions for acid-loving plants, such as blueberries and azaleas, or to lower the pH of alkaline soils. The fine particle size of peat moss, when fully dry, can make it difficult to re-wet, and its decomposed nature offers less long-term structural integrity and aeration in a soil mix.