Mosses, like most lawn weeds, primarily take advantage of bare areas but do not kill out existing grass as some people believe. Bare areas in lawn can result from several causes. Unsuitable grass varieties, poor drainage, drought, soil compaction, excessive shade, thatch accumulation, poor fertility, diseases, improper mowing and other cultural practices are common reasons for turf failure leading to moss or other weed problems. Improving these factors to encourage thick, healthy grass is the key to long term prevention.
Moss can be killed with products containing ferrous sulfate, ferrous ammonium sulfate, including Moss-Out, Moss-Kil, Rid-Moss, and a variety of lawn fertilizers with moss control; or moss & algae killing soaps such as Safer’s. None of these materials pose serious threats to the environment; in fact iron and sulfur are essential nutrients for grasses and tend to improve their color. Although these products will kill existing moss, unless the underlying conditions are changed, moss or other weeds are likely to reappear.
Raising the soil pH with agricultural or dolomitic lime can improve availability of nutrients and supply calcium thus helping the turf grow better, but will not kill moss directly. The following steps will generally control existing moss and discourage it in the future:
1.Use a moss control product to kill existing moss in late winter or early spring.
2.Dethatch or rake out dead moss, or skip step (1) and dethatch or rake with more vigor.
3.Over seed bare areas with the recommended turf type for your area.
4.Top-dress seeds with about l/4 inch of loose weed-free soil, or potting mix.
5.Keep seeded area moist until seedlings are established.
6.Maintain the lawn according to recommendations from your local Extension Office.
Cooperative Extension System Offices
Courtesy of Steve Whitcher, Master Gardener Program Coordinator, Washington State University.