Moss is a non-vascular plant that thrives in damp, shaded environments, often appearing as dense, green carpets on surfaces like lawns, walkways, and roofing materials. Moss lacks the true roots and extensive internal water transport systems found in higher plants. On structures like roofs, moss growth can trap moisture, dislodge shingles, and accelerate material decay, leading to significant structural problems over time. This common problem prompts many homeowners to seek quick, accessible solutions, leading to the popular query regarding the effectiveness of household laundry detergent as a moss killer.
How Detergent Affects Moss
The direct answer is yes, laundry detergent can eliminate moss, but the result is often localized and temporary. When detergent is applied directly, the moss quickly reacts by turning brown or black, showing visible signs of dying within hours or days. This rapid discoloration is the consequence of severe cellular damage and subsequent dehydration. Homeowners note that the treated moss dries out and can be easily scraped or washed away afterward.
However, this method rarely provides a lasting solution because it only treats the visible portion of the plant. Mosses reproduce readily through spores and tiny fragments. The underlying conditions that promoted the initial growth, such as excessive shade and moisture, are not addressed by the detergent application. Residual spores and surviving fragments will often regrow quickly once the chemical concentration dissipates and moisture returns.
The Chemical Mechanism of Action
The destructive power of laundry detergent against moss stems from two primary chemical components: surfactants and alkalinity. Surfactants are compounds designed to lower the surface tension of water and interact with both water-soluble and fat-soluble materials. These molecules disrupt and dissolve the lipid membranes that encapsulate all living cells.
When surfactants make contact with the moss, they bombard the delicate cell membranes, which are essentially lipid bilayers. This compromises the membrane structure, leading to increased permeability, leakage of cellular fluids, and ultimately, cell collapse. Moss is especially vulnerable because, unlike vascular plants, it lacks a protective waxy cuticle that would shield its tissues from external agents.
Most laundry detergents are highly alkaline, often possessing a pH around 9. Moss prefers a slightly acidic environment, and this sudden increase in pH severely stresses the plant’s sensitive cellular functions. This chemical stress, combined with the membrane-dissolving effect of the surfactants, causes rapid, irreversible damage, resulting in the moss quickly losing its internal moisture and dehydrating.
Environmental and Surface Damage Risks
Despite its effectiveness in killing moss, experts strongly advise against using laundry detergent due to the significant environmental and material damage it can cause. On roofing surfaces, detergent acts as a potent degreaser, which is highly detrimental to asphalt shingles. Shingles rely on a layer of asphalt, tar, and oil to protect the underlying fiberglass mat from the elements. The detergent strips away these protective components, accelerating the wear of the roof and potentially shortening its lifespan by up to half, leading to costly repairs.
The application of detergent also creates an immediate safety hazard, particularly on sloped surfaces. Once the detergent is moistened, it becomes extremely slick and slippery, creating a high risk of falls for anyone attempting to apply the product or remove the dead moss. Beyond the immediate surface damage, the runoff from the detergent poses a serious threat to surrounding landscaping and water systems.
As the detergent is washed away by rain or rinsing, it carries high concentrations of surfactants and other chemicals into the soil, altering the soil’s pH and potentially inhibiting the growth of grass, shrubs, or other plants. When these chemicals enter storm drains and waterways, the surfactants reduce the water’s surface tension. This reduction negatively impacts aquatic life by interfering with gas exchange and proving toxic to sensitive microbic flora.
Recommended Methods for Moss Control
A more reliable and safer approach to controlling moss involves using specialized treatments and addressing the environmental factors that encourage moss growth. Chemical options proven effective against moss primarily rely on compounds that cause rapid cellular desiccation without the severe side effects of detergent. Products containing iron sulfate, also known as ferrous sulfate, are highly effective, causing the moss to dry out, turn black, and die.
Another commercial alternative is the use of products formulated with potassium salts of fatty acids, which function similarly to a soap but are designed for horticultural use. These soaps work by dissolving the moss’s outer layers, leading to dehydration and death, and are generally considered safer for the environment than household detergents. After any chemical treatment, the dead moss must be physically removed, usually by raking or scarifying, to prevent it from simply decomposing in place.
For long-term success, the underlying causes of moss proliferation must be corrected, as moss is an indicator of poor growing conditions for turfgrass and other preferred plants. This involves improving drainage in the area, as moss thrives in overly moist soil. Aerating compacted soil and pruning overhead trees and shrubs to increase sunlight exposure and air circulation will also discourage moss growth. Finally, testing and adjusting soil pH, often with an application of lime to reduce acidity, helps create an environment more favorable to healthy grass and less welcoming to moss.