Moss is a problem in many lawns, but it is somewhat misunderstood. It does not kill grass, rather it grows in grass that it not taken care of properly. Moss travels easily in thin, weak grass, reproducing when it rains by spreading spores. Controlling moss in a lawn requires the right lawn care to improve the grass spread and quality.
Proper fertilization of the lawn increases grass coverage and strength as well as balancing out the soil acidity. Applying at the right time and in the correct amount, says the Maryland Cooperative Extension, encourages root development, preventing thin grass due to drought. Late summer to the early fall is the correct time to fertilize turf grass lawns. Summer fertilization damages grass and increases top growth which retains moisture in the lawn, encouraging moss growth.
Soil acidity, or the soil pH, determines whether or not grass will grow well. Soil that is slightly acidic, between a 6.0 and 6.8 range is desirable for turf growth, while soil that is greatly acidic will prevent grass from growing. A pH test of the soil acidity will determine the quality of the soil. If the soil acidity is high, indicated by a low pH number, lime is used as an additive to the soil to raise the pH. Lime should only be added to the soil if a pH test indicates a need says the University of Illinois, and not as a remedy for moss.
Moss thrives in moist conditions. If the lawn soil is compacted due to human or animal activity on the surface, closing off the soils pores, the lawn will not drain water properly. Also, compacted soil restricts the movement of grass roots through the soil. Aeration is a method of removing 3 to 4 inch plugs of dirt from the lawn using either a hand held tool with hollow spines at the end, which is plunged into the soil to remove dirt plugs, or a mechanical device that does it for you. Aeration is required once a year in the fall to reduce soil compaction.
Mowing properly ensures a dense canopy and reduces stress to grass blades when cut. It is recommended that only 1/3 of the grass blade is removed at a time to reduce thatch, dead plant matter that prevents water and fertilizer from reaching the soil, and to encourage root growth. Also, grass height should be kept between 2 and 3 inches to reduce sun stress, a condition in which moss can thrive.
Moss thrives in wet conditions, so it is important only to irrigate when necessary to prevent water damage to grass, and for the prevention of puddles on the soil. Deep watering encourages root growth. The Maryland Cooperative Extension recommends penetrating the soil to a depth of 4 to 6 inches, and avoiding shallow watering that reduces root depth.