Algae and moss produce green slimy growth in lawns. Algae and moss are small green, primitive threadlike plants without roots. They do not kill grass but form an unsightly thick mass. Mosses and algae in a lawn mean that it is not a healthy environment for grass plants but favorable for these primitive plants. Take steps to improve the conditions in your lawn and eliminate moss and algae problems.
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Fertilizer and pH Adjustments
Test the lawn soil from healthy grass areas and from areas where green slimy algae and moss are growing. State universities will conduct a soil test for you. Moss and algae grow in areas where grass is not growing because of unhealthy conditions. Fertilize the lawn with the recommended concentration from the soil test. Moss and algae grow in acidic soils. Amend the lawn with lime if the pH is lower than 5.8, as most turf grass species prefer a pH of 5.8 to 6.5.
Soil Compaction and Soil Drainage
Grass does not grow vigorously in compacted soil with poor water drainage because grass roots are unable to penetrate compacted soil. Moss and algae prefer wet conditions and do not have roots. Add sand or soil to alter the lawn’s elevation if the wet area is small. Install tile drains if the wet area is large. According to Alabama Cooperative Extension, use a 1/2- to 3/4-inch metal pipe soil probe and take a few plugs from the problem area. Penetrate the soil 4 to 6 inches. Check for roots in the plugs. Grass roots should extend up to 6 inches into the soil. If no roots are found, the grass is shallow-rooted because of compactness. Core aerate compacted soil with a spading fork or sod-coring tool.
Shade and Air Movement
Dense shade favors algae and moss growth while most turf grasses do not grow well with low levels of sunlight. Remove trees that provide too much shade, and prune away lower branches if you want to have a lawn rather than shady areas. If not, use shade-tolerant ground covers or mulch to eliminate grass from the shady area. Prune shrubs to allow more air movement into the shady area and eliminate excess moisture.
Control moss and algae by dissolving 3 oz. of copper or iron sulfate in 5 gallons water, according to Purdue University Cooperative Extension. Spray over 1,000 square feet. Use a metal container, and be careful of clothing because these chemicals stain. Control algae by applying 3 lbs. of hydrated lime per 1,000 square feet. This is a temporary control and reapplications could damage the turf.