Moss is a non-vascular plant that thrives where turfgrass or other plants struggle to grow. While natural, its presence is often a nuisance for homeowners, ruining the aesthetic of lawns and gardens. Moss forms thick, green mats that can create slippery hazards on hard surfaces like walkways and decks. In lawns, moss competes with turfgrass for space, thinning the grass and creating an uneven, patchy appearance.
Identifying Environmental Conditions That Encourage Moss Growth
Moss signals underlying environmental conditions that prevent healthy growth, especially for turfgrass. The primary factors are excessive moisture and low light, which moss tolerates well but grass does not. Poor soil drainage creates persistently wet conditions, which are favorable for moss growth.
Compacted soil restricts air and water movement, leading to poor drainage and a stressed lawn. Moss also favors low, acidic soil pH, which inhibits turfgrass from absorbing necessary nutrients. When these conditions are present, the grass thins out, allowing moss to colonize bare patches.
Physical Removal Techniques
Physical removal is a direct method for immediate, temporary moss control. In a lawn, vigorous raking or dethatching is effective because moss lacks true roots, relying only on small rhizoids for anchoring. Moss mats can be easily lifted from the soil surface using a stiff-tined rake or a power dethatcher for larger areas.
For hard surfaces like patios, walkways, and decks, use a stiff-bristle brush or scraper. Pressure washing quickly clears large areas but must be done carefully to avoid damaging underlying materials, especially roofs. Physical removal is a short-term solution, and the moss will return unless the underlying conditions are changed.
Treatment Options for Eradication
Chemical treatments kill moss quickly, but the product choice depends on the surface being treated. For lawns, the most effective chemical is iron sulfate (ferrous sulfate). When applied, iron sulfate rapidly desiccates the moss, causing it to turn black within a few days, making it easier to rake out. Because iron sulfate can cause rust-like staining on concrete, pavers, and wood, it must be applied only to the lawn.
For hard surfaces where staining is a concern, commercial moss killers containing zinc sulfate or copper sulfate are often used. These compounds kill the moss without the staining risk of iron-based products. Alternatively, household products like a diluted solution of dish soap or baking soda can be applied to hard surfaces to dry out and kill the moss.
When using any treatment, follow instructions precisely and take precautions to prevent runoff. Runoff containing these chemicals can be toxic to aquatic life if it enters storm drains or waterways. After the moss is killed, it must be physically removed to prevent the dead layer from impeding future grass growth.
Modifying the Environment for Long-Term Control
Achieving long-term control requires addressing the root causes that allowed the moss to thrive. Improving soil drainage is a fundamental step, often accomplished through core aeration, which removes small plugs of soil to alleviate compaction and allow water and air to penetrate. For significant drainage issues, incorporating organic material or sand can improve soil structure, or grading the landscape may be necessary to ensure proper water run-off.
Light penetration is another factor, as excessive shade creates the cool, moist environment moss favors. Pruning low-hanging branches and thinning the canopy increases sunlight, making the area less hospitable for moss and more suitable for grass. Increased light also promotes better air circulation, helping surfaces dry out quickly.
To correct low soil pH, a soil test should determine the exact level of acidity. If the pH is below the optimal range of 6.0 to 6.8 for turfgrass, applying lime, such as calcium carbonate, can raise the pH. Correcting the soil pH helps the grass absorb nutrients efficiently, encouraging a dense lawn that naturally crowds out the moss. If shade cannot be reduced, planting a shade-tolerant groundcover or grass variety, such as fine fescue, is a practical alternative.