Moss is an ancient plant species from the plant group called bryophytes and comes in nearly 15,000 different recognized varieties. The plants start to grow when the spore finds optimal conditions for germination, leading to the growth of horizontal and upright filaments that appear fuzzy from a distance. Mosses continue to grow and live indefinitely provided optimal growth conditions.
Mosses are noncompetitive plants that thrive in poorly-managed grass and landscape areas and in sites that do not support the healthy growth of plants. Contrary to popular belief, moss does not cause lawns to die but starts to grow in already declining grass. Conditions that favor moss growth include poorly fertile and acidic soil, soils with poor drainage, compacted soil and shaded areas. Nonaggressive turfgrass species that are mowed very short are also prone to moss growth.
Given favorable conditions, mosses thrive and spread. Getting rid of moss is nearly impossible unless the cultural conditions are corrected to be less inviting. Unless this is done, moss will start to grow again. If the cultural conditions cannot be corrected, the Cornell Cooperative Extension recommends letting the plant grow as a permanent ground cover. Even the use of moss control chemicals are not a long-term solution as long as favorable growth conditions continue to exist.
Increase the soil pH in lawns and improve soil drainage by adding dolomite lime. Aerate and dethatch lawns to reduce compaction. These steps will reduce moss over time and are not a quick fix. Rake out moss, and overseed any bare landscape areas. Use chemical control options during late winter or early spring. Fertilize lawns that are prone to moss infestations on a regular basis and overseed yearly.
The most commonly used moss control products contain iron sulfate as the active ingredient, cite Ed Hume and James Hume in "Gardening with Ed Hume." Treat moss when temperatures are between 45 to 65 degrees F. Application of the chemical will turn the moss black and kill it. Read directions carefully as some manufacturers recommend watering the areas prior to treatment while others recommend irrigating it later. Avoid getting iron sulfate on concrete areas as it will create stains. Do not use lawn moss killers for moss control on rooftops.