Moss growth on roofs, walkways, and lawns is a common frustration for property owners, often signaling underlying issues like excessive shade or poor drainage. Many people seeking a fast, affordable fix consider using ordinary table salt (sodium chloride) as a homemade moss killer. This approach raises important questions about its effectiveness and safety. The answer to whether salt kills moss is nuanced, depending heavily on the unintended consequences of its use.
How Salt Affects Moss and Application Guidance
Salt can effectively kill moss by disrupting its cellular structure. Mosses are non-vascular plants, absorbing moisture and nutrients directly from their environment. When a strong brine solution is applied, the high salt concentration creates an osmotic pressure gradient. This process, known as osmosis, draws water out of the moss cells, causing rapid dehydration and death.
To use this method, dissolve salt into water to create a saturated solution, then spray or pour it directly onto the moss colonies. The application must thoroughly saturate the moss without excessive runoff. This technique dries out the moss quickly, and once it turns brown or black, it can often be scraped away easily.
Why Salt Usage Poses Significant Risks
Using sodium chloride salt introduces significant environmental problems. The primary concern is soil salinization, where salt leaches into the surrounding soil and accumulates, raising its overall salinity level. This excess sodium and chloride is toxic to most turf grasses, shrubs, and garden plants. High salt concentrations cause a physiological drought, making it difficult for plants to absorb water even when the soil is wet.
Salt runoff can travel beyond the application site, flowing into storm drains and contaminating local waterways. The chloride ions can harm aquatic life and alter the ecological health of streams. Concentrated salt solutions also damage hard surfaces over time. Repeated application may corrode metal flashing and degrade paving stones or concrete surfaces.
Effective, Non-Toxic Alternatives for Moss Removal
Safer, more responsible methods exist for removing moss without creating lasting environmental damage. Physical removal is the safest option, involving scraping or brushing the moss off hard surfaces and aerating or dethatching it from lawns. For hard surfaces like roofs and walkways, commercial moss killers containing potassium salts of fatty acids (soap) are highly effective. These contact herbicides disrupt the moss’s cell membranes, causing them to die quickly. They are generally biodegradable, non-staining, and do not harm adjacent plants when used as directed.
Another common alternative is ferrous sulfate (iron sulfate), which rapidly turns the moss black within hours or days. Ferrous sulfate is often used on lawns because the iron acts as a beneficial nutrient for the grass, but be aware it can permanently stain concrete or stone if not carefully applied. The most effective long-term strategy involves addressing the root cause, such as improving drainage, trimming trees to increase sunlight exposure, and ensuring proper soil pH to favor grass growth over moss.