How to Remove Algae Mold on the Lawn

Reduce watering your lawn. Algae will form when grass and soil are water logged or the lawn is located in an area that receives high humidity. Check that the lawn needs water before adding water to the soil, and turn off automatic irrigation systems that may be filling the lawn with more water than it needs. If you still have sitting water on your lawn, dig small pits in low areas and back fill the pit with sand. Water will drain into the pit and away from the grass, reducing the overall moisture in the grass.

Check the pH level of your lawn with a pH test kit. You can purchase a pH testing kit from your local university extension office. Most grass requires a pH between 5.8 and 6.5, except for centipede grass, which could have a pH between 5.5 and 6.0. If the pH level is low, add dolomitic lime to your lawn. Adding lime will raise the lawn's pH level and discourage algae growth.

Take or send a sample of your lawn and soil to a local university extension office. For a small fee, the lab will test your soil and let you know what, if any, nutrients are lacking in the soil. Supplement those lacking nutrients with a water-soluble lawn fertilizer. A fertilizer may not kill algae, but it will strengthen your grass so that it will not suffer or succumb to any algae scum presence.

Apply an algae killer product to the lawn between December and April when the lawn is moist. You can find various types of algaecides in a home and garden store. Follow the label instructions and warnings carefully. You can make a homemade algae killer by adding 5 oz. of copper sulfate to 4 gallons of water, which is enough to spray over 1,000 square feet of lawn.

Remove any dead algal crust from the lawn with your hands or a rake.