Moss commonly invades nutrient-poor, shaded lawn areas when conditions are mild and wet. In many areas, moss can begin growing where the grass is weakened, beginning during rainy autumn months and peaking the following year in early spring. Mosses grow vigorously in lawns during winter months that are mild enough to promote moss growth but cold enough to send the lawn grass into dormancy.
The key to getting rid of lawn moss is to address the environmental factors contributing to its growth. If you don't fix these, any other remedy you try will prove to be only temporary. Moss usually appears in shady areas of lawns, where soil fertility is poor, and the soil is compacted and has poor drainage. These conditions not only provide an ideal environment for moss to grow, but they also weaken the lawn grass. Cultural fixes include planting more shade-tolerant grass types or ground covers in the affected lawn areas, mowing the grass in shady areas at the tallest possible height to promote deeper rooting and pruning tree limbs around the area to provide more sunlight exposure to the grass. For deeply shaded lawn areas, you may want to consider removing some of the trees or shrubs that are shading the grass. You can also apply a lawn fertilizer to boost fertility.
Some home remedies do exist for getting rid of lawn moss, which aren't too harsh on your soil or surrounding grass. You can dissolve a small box of baking soda in 2 gallons of lukewarm water and spray the mixture onto the moss. Let the mixture dry on the moss, and then remove the dead moss.
Mechanical control of lawn moss is usually employed along with a chemical or homemade remedy. Mechanical control consists of digging out the moss patches using a shovel and core-aerating the lawn area. You'll need to reseed the area with a strong, shade-tolerant grass type and top-dress the area with a fine-textured organic compost or topsoil. You can also dethatch the lawn area in early spring to get rid of most of the moss, using a flail-type dethatcher. After dethatching, apply a nitrogen-based lawn fertilizer to encourage grass growth.
Chemical controls are a remedy of a last-resort for severe lawn moss invasions or persistent mosses. Some chemical products are commercially available, such as cryptocidal soaps that are targeted specifically to kill moss that you can apply at a rate of 2 1/2 quarts per 1,000 square feet of lawn area. Many moss-removing chemicals contain salts and chelated iron, which you can apply to the affected lawn areas at a rate of a half to 1 lb. of iron per 1,000 square feet of lawn. If the iron product is in dry form, apply the chemical at a rate of eight-tenths to 1 1/2 lbs. per 1,000 square feet of lawn.