Moss is a common material in container gardening, but the term refers to several distinct products with unique functions. Gardeners incorporate moss into potted plants to improve water management, enhance the growing medium’s structure, or for decoration. Understanding the differences between these materials and their specific applications is necessary to determine if moss is beneficial for a plant’s health.
Understanding the Different Moss Types
The products labeled as moss fall into three main categories, each derived from the Sphagnum genus or other moss types. Sphagnum Peat Moss is a highly decomposed, dark-brown material harvested from deep within bogs, where it has formed over thousands of years. It possesses a fine, short-fibered texture and is primarily used as a soil amendment.
Long-Fiber Sphagnum Moss consists of the living or dried, minimally decomposed strands of the Sphagnum plant taken from the bog’s surface. This material is identifiable by its long, flexible fibers and spongy feel, allowing it to hold significant water while remaining airy. Sheet Moss or Live Moss comprises various other types of mosses and is generally used intact for aesthetic purposes or as a top dressing.
Moss as a Potting Mix Component
Sphagnum Peat Moss is a widely used component mixed directly into potting media to alter its physical and chemical properties. Its unique cellular structure allows it to absorb and retain a large volume of water, often up to 20 times its dry weight, making it an excellent moisture stabilizer. By retaining this moisture, peat moss reduces the frequency of watering needed, which is helpful for plants in fast-draining mixes.
The addition of peat moss also improves soil aeration and prevents compaction, especially in heavier mixes. The fibrous material creates air pockets, ensuring oxygen can reach the roots for healthy growth. Peat moss naturally has a low pH, typically ranging between 3.0 and 4.5. This makes it beneficial for acid-loving plants such as ferns, orchids, African violets, and carnivorous species. Incorporating this material helps maintain the slightly acidic environment these plants prefer and can buffer the effects of alkaline tap water.
Using Moss as a Surface Layer
Applying moss, typically Long-Fiber Sphagnum or Sheet Moss, as a top layer serves both practical and decorative functions. This layer acts as a mulch, reducing water evaporation from the soil beneath and maintaining consistent moisture in the root zone. Covering the soil also offers a cleaner appearance and can discourage pets from digging in the container.
Long-Fiber Sphagnum is also employed in specialized applications, such as lining wire hanging baskets or in the air layering propagation technique. In air layering, the hydrated moss is wrapped around a wounded plant stem and sealed to create a moist environment that encourages new root formation. When using any moss as a top dressing, ensure it is not packed tightly against the plant’s crown or stem base, as constant moisture in this area can promote fungal diseases or rot.
Cautions and Environmental Considerations
While moss offers many benefits, its use comes with certain practical and environmental concerns. Peat moss, when allowed to dry out completely, can become hydrophobic, meaning it actively repels water. Water poured on a dry peat-based mix will often run down the sides of the pot rather than soaking into the root ball, leaving the plant dehydrated. Rehydrating a hydrophobic mix requires soaking the entire pot in water for an extended period.
A top layer of moss, especially if kept constantly damp, can create an ideal breeding ground for fungus gnats, whose larvae feed on plant roots. The constant moisture retained by the moss attracts these pests by offering a moist surface for egg-laying.
Additionally, the widespread harvesting of Sphagnum Peat Moss from natural bogs raises sustainability issues. These bogs are complex ecosystems that take thousands of years to form and act as significant global carbon sinks. When peat is harvested, the stored carbon is released into the atmosphere, contributing to climate change, which has prompted some regions to implement restrictions on its sale.