Peat moss and sphagnum moss are often confused, though they represent different stages of a single plant’s life cycle and serve distinct purposes in horticulture. While intimately related, the distinction is between a living or recently dried plant material and a product of ancient, geological decomposition. Understanding this relationship clarifies their proper applications and environmental implications.
Sphagnum Moss: The Living Plant
Sphagnum moss originates from the plant genus Sphagnum, which thrives in wet, acidic environments called bogs. When dried, the plant is recognizable by its light green or tan color and possesses a distinct, fibrous, and spongy structure. Its capacity to hold water comes from specialized, large dead cells known as hyaline cells, which make up around 80% of the plant’s volume.
These dead, empty cells have pores that allow them to absorb and retain an impressive amount of moisture. This structure provides a large water-holding capacity, which is a factor in the formation of peatlands. Commercially, sphagnum moss is sold as long, dried strands valued for their structural integrity, helping maintain air pockets and prevent compaction.
Peat Moss: The Decomposed Soil Amendment
Peat moss is the end product of Sphagnum and other plant decomposition occurring over thousands of years. This transformation happens in the deep, waterlogged layers of a bog under strictly anaerobic conditions, meaning they lack oxygen. The absence of oxygen and low temperatures drastically slow the rate of decay, allowing organic matter to accumulate instead of fully breaking down.
This geological process takes an immense amount of time, with peat layers accumulating slowly, often ranging from 0.5 to 1 millimeter per year. The resulting material is dark brown, highly decomposed, and possesses a fine, uniform texture. Peat moss is strongly acidic, usually registering a pH between 3.0 and 4.5, making it a popular soil amendment for acid-loving plants and a component in many commercial potting mixes.
Practical Differences in Horticultural Use
The distinct physical and chemical properties of the two materials dictate their separate uses in horticulture. Peat moss, with its fine texture and high acidity, functions primarily to modify the properties of soil or potting mix. Gardeners incorporate it to increase the mix’s ability to retain water and nutrients, or to lower the soil pH for certain plants like blueberries, rhododendrons, and camellias.
Long-fibered sphagnum moss is prized for its physical structure rather than its chemistry, often having a more neutral pH. It is used in applications requiring a light, airy, and moisture-retentive medium, such as for orchids and carnivorous plants. This includes lining wire hanging baskets or facilitating air layering to propagate cuttings. Sphagnum moss helps ensure adequate air circulation around delicate roots, preventing the compaction that can occur with fine-textured peat moss.
Sustainability and Environmental Concerns
The formation of deep peat deposits is a geological process, rendering peat moss a non-renewable resource on a human timescale. Peatlands are globally significant carbon sinks, storing more carbon than all the planet’s forests combined. While the living Sphagnum plant can regenerate quickly, the underlying peat takes thousands of years to accumulate.
When bogs are drained and peat is harvested, the stored carbon is exposed to oxygen and oxidizes, releasing carbon dioxide into the atmosphere. This release contributes directly to greenhouse gas emissions and climate change. Large-scale extraction also destroys unique and fragile bog ecosystems. Due to these consequences, many gardeners and commercial growers seek sustainable alternatives, such as coco coir, composted wood fibers, and rice hulls, to replace peat moss.