Moss in Lawns

The occurrence of moss in lawns is a common problem for many homeowners. Moss is usually associated with grass management problems and/or soil and site characteristics. Mosses are small, leafy plants that appear to be a mass of fine stems. They vary greatly in size and do not have roots, but rather form root-like filaments that attach to soil and other substratum.

Mosses can grow and out-compete grass species when one or more of the following occur: high or low soil pH (some species appear to be associated with acid and others with alkaline conditions), low soil fertility, shade, poor soil drainage, and soil compaction. Mosses are adapted to a wide range of environmental conditions – some grow well in dry areas, while other grows best in bog-like habitats. Although moss is often found in shady spots, it can also grow and thrive in sunny locations. An application of agricultural lime is not likely to solve a moss problem; however, applying hydrated lime may cause injury by dehydrating or burning the moss plant.

Cultural Control

The best way to control moss is to change the conditions that favor its growth.

Soil nutrition. The first step in controlling moss in a lawn is to determine the nutritional status and pH of the soil. Do a soil test. The report will make appropriate suggestions for fertilizer and lime applications to correct any deficiencies. When grass species are growing under conditions of poor fertility, they are weak and are therefore unable to compete with encroaching mosses.

Soil drainage. Soils that are constantly wet because of poor drainage should be contoured so that water will drain away from the lawn. If moss is present in low areas of a yard or if soil drainage is a problem, it is important to determine if and how these problems can be remedied. Drainage tiles can be effective in many circumstances. However, it is important to determined the effects of the excess water on the adjoining areas.

Shade. At least 3 – 4 hours of full sunlight or 6 – 8 hours of filtered sunlight are necessary to grow grass. If heavy shade is a problem, trees may need to be pruned and a "shade" grass seed mix used for the area. Rough bluegrass is highly shade tolerant and the fine fescues as a group tolerate shaded conditions. When moss is troublesome in grass under trees, there is often little that can be done. In these situations, perhaps shade-tolerant groundcovers such as pachysandra, English ivy, or myrtle should be considered.

Compacted soil. Heavy soils can be amended by incorporating several inches of sand, compost, or other sources of organic matter into the soil. These amendments may help to improve both soil texture and drainage.Compacted soils can also be aerated where it is undesirable to till the soil surface.

Improve Air Circulation. Low-branched trees may be the cause of poor air circulation, as well as dense shade. Lawns surrounded by buildings and high vegetation with limbs close to the ground will require considerable effort to provide adequate air circulation to grow a good lawn.

Chemical and Mechanical Control

Moss can be physically eradicated by mechanical removal and hand raking with a stiff-tined rake. However, control may only be temporary if the reason(s) for the infestation is not established or remedied as described above.

Moss can also be controlled through the use of chemicals containing ammonium sulfate. Since mosses usually grow most vigorously during the cool moist conditions in the fall and spring, these are the best times to apply chemical moss killers. (General-use herbicides for weeds do not work on moss.) Different compounds are registered for use in different states. Consult your local Cooperative Extension service and read product labels for dosage rates and safety precautions.

Adapted from: David P. Martin and Keith J. Karnok, Ohio State University Extension, 2001; Dr. Sharon M. Douglas, The Connecticut Agricultural Experiment Station, 2006