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Work on soil conditions to control moss in lawns

Frequently the Extension office receives phone calls from homeowners who are concerned about moss growing in their lawns. The presence of moss indicates the cultural conditions of the lawn are not right for the growth of healthy turfgrass. If your lawn has areas with moss, carefully evaluate the site conditions and your turf care practices.

Mosses are primitive green plants with tangled branching stems and small leaves that form mats on the soil under favorable conditions. They reproduce by wind blown spores. These small plants, by themselves, do not harm the turfgrass but mosses can form crusts over the soil and reduce the infiltration of air and water.

They flourish in shade, and in soils that are poorly drained, compacted, acidic and low in fertility. Any one of these conditions, or a combination of them, will encourage the growth of moss.

If excessive amounts of shade are causing moss to grow, consider planting a shade tolerant turfgrass. Tall fescue, St. Augustine grass, and some varieties of zoysia can grow in filtered shade. However, if the area receives less than four hours of sun per day or is in deep shade, the site lacks the necessary amount of sunlight to grow healthy grass.

As an alternative, consider mulching the area with pine straw, pine bark, or planting shade tolerant groundcovers like liriope, mondo grass or Japanese pachysandra. The amount of sunlight reaching the area can be increased by removing tree limbs growing within ten feet of the ground.

In areas with poor drainage and standing water, moss thrives. Drainage can be improved by incorporating organic matter to the soil to raise the elevation and to allow for better infiltration of water. Low areas can be trenched or have their contours altered. For larger areas that stay wet for prolonged periods of time, consider installing a French drain or drain tiles to carry away the excess water.

The application of too much supplemental water can cause water to puddle and contribute to poor drainage. The rate and frequency of watering needs to match the soil conditions, the water requirements of the turf, and the prevailing weather conditions.

Poor soil fertility combined with a low pH weakens turfgrasses preventing them from competing with the encroaching moss. Consider having the soil tested through Gwinnett County Extension for pH and nutrient levels. The cost is $8 per sample. Turfgrasses prefer a soil pH of 6.0 to 6.5 except centipede grass, which grows best in soils with a pH of 5.5 to 6.0. To raise the pH, add lime to the soil. It does not kill the moss, but will improve growing conditions for the turfgrass. If the soil lacks the necessary nutrients needed to grow healthy turfgrass, fertilize according to soil test recommendations.

Compacted soils inhibit the infiltration of air and water creating a favorable environment for the moss. Excessive foot traffic and lawn mower usage contribute to the problem. Turfgrass root systems suffer under these conditions. To find out if your soil is compacted, use a small shovel and try to remove a four inch deep section of the soil. If you have a hard time getting the shovel to penetrate into the ground, the soil is compacted. If the turfgrass roots in the sample are growing only in one inch or less below the soil’s surface, then corrective action needs to be taken. Healthy root systems should be growing at a depth of four to six inches. To remedy the problem, use a hollow tine aerator or a steal rake to break up the compacted layer of soil to enhance drainage and air exchange.

Moss can be eliminated by the application of chemicals labeled to control it such as Bayer Advanced 2-in-1 Moss and Algae Killer, iron sulfate or copper sulfate. These chemicals cause the soil to dry out. To be effective, the chemicals need a 24-hour rain-free period after application. As the moss begins to die, it will turn an orange-brown color. After dying, remove by the dead moss by raking.

Even though moss can be eliminated by chemical or mechanical means, the moss will eventually return if the cultural conditions that favor the growth of healthy grass are not implemented. Otherwise the grass will continue to die out and the moss will prosper.

Timothy Daly, is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or tdaly@uga.edu.