Moss is a prevalent lawn pest, attacking patchy, unhealthy lawns. Poor drainage, drought, compact soil, excessive amounts of shade and poor fertility are all causes of lawn moss says the Washington State University Extension. There are several chemical controls to deal with lawn moss, but without maintaining a healthy lawn, moss will return with time. A balanced mixture of cultural controls, along with chemical treatment, will keep the lawn moss free.
Apply a lawn moss and algae control soap to the afflicted areas of the lawn according to the manufacturer's instructions on the packaging. Service in the winter or early spring.
Rake the lawn to remove dead moss.
Aerate the lawn with a core aerator machine to improve drainage in the soil, preventing the moist conditions needed for moss growth. Aeration removes small plugs of soil from the ground and reduces thatch. Run the core aeration machine in a criss-cross pattern along the lawn to ensure maximum coverage.
Eliminate grass in areas that are too shady for the grass to grow or cut away tree limbs or shrubs that are blocking out the sun, improving coverage and air circulation.
Overseed the lawn using a winter grass seed such as ryegrass. Apply 10 pounds of ryegrass seed per 1,000 feet, or 5 to 15 lbs for other perennial grasses. Apply a 1/4-inch layer of loose soil as a topdressing and moisten with an inch of water.
Fertilize the lawn in April or early June with 2 lbs of nitrogen per 1,000 square feet. Add another application in September to encourage good growth before the winter dormancy period.