Moss, a velvety green plant organism, grows on exterior concrete surfaces that are not exposed to sunlight and remain in a persistently moist state. While moss is not harmful to concrete, its presence on concrete patios and walkways can make them more slippery, causing a safety hazard. These growths can be effectively removed using a chemical control method. Start with the least toxic, only applying another method if the first is not effective.
Carefully pour the boiling water over the area affected by moss. This is the most environmentally friendly application. Scrub with stiff brush or broom and wash away debris with hose.
Sprinkle agricultural lime or baking soda on affected areas to kill moss. These chemically basic powders help neutralize the acidic conditions mosses thrive in. Let set 24 hours, then carefully sweep up, and dispose of powder
Put on rubber gloves and old clothing. Apply regular household bleach to your moss with a sprayer. The recommended mixture is 1 part water to 1 part bleach concentrate. Spray to cover the area and leave it on for 30 seconds, then brush and hose off. Again, damage to clothing, other plants and grass is possible, so follow directions on bottle carefully. The use of this method may keep moss from regrowing for up to one year. Brands of bleach specifically concentrated for killing mosses can be found in most garden centers.
Put on safety gear. Mix a solution of 3 pounds of zinc sulfate with 5 gallons of water and apply to mossy areas. The product is said to be effective for two to five years. It can damage surrounding plants, so these should be covered during the application process. It is also toxic to fish and should not be applied near water.
Don safety gear. Apply ammonium sulfamate to the moss on your concrete. Ammonium sulfate is sold in garden supply stores under a variety of brand names such as Amcide, Amicide, Amidosulfate, Ammate, Ammate X-NI, Fyran 206k, Ikurin, Silvicide, and Sulfamate.). Follow manufacture's guidelines for application. It is generally applied using a sprayer or watering can with a sprinkling spout, drenching all areas of concrete where moss is a problem. Avoid desirable flora including trees or shrubs. Choose a day or time when the air is still to circumvent damage to other plants. Be sure to read label carefully before use and follow all manufacturer's directions.
Use a power sprayer to clear the area both of moss debris and chemical residue after any of these treatments.