A: Many times the turf area begins to thin because the conditions for growing dense, healthy turf have declined. A good example is trying to grow Bermuda in filtered sun. Bermuda needs full sun to do well.
I see this all the time with Bermuda because for the last 20 years or more, whenever a new house is built, Bermuda sod is planted because it is the cheapest. The homeowner plants a shade tree or two, or young existing trees grow bigger, and over a period of years the trees cast shade on the Bermuda, it thins out, and many times this moss grows.
Mosses are branched, threadlike plants that form a tangled, thick mat over the soil. It is not considered parasitic and it is spread by wind blown spores. It can form crust on the soil surface which reduces air and water movement into the soil.
Factors that favor the development include wet and humid conditions and compacted soils with thin turfgrass. It is more common in shady areas with infertile, acidic soils.
Cultural practices that favor the growth of turfgrass will reduce the competition from moss. These practices include:
MAINTAIN GOOD SOIL FERTILITY AND PH: Have your soil tested to determine the proper lime and fertilizer needs. For most turfgrasses, the pH should be between 5.8 and 6.5.
IMPROVE DRAINAGE: Soils that stay moist because of poor drainage should be contoured so that water will drain off the area. In some cases, tile drainage may be necessary to correct wet conditions.
INCREASE LIGHT PENETRATION AND AIR CIRCULATION: Pruning tree limbs below 10 feet and selected limbs in the crown will improve light penetration and air movement. Also removing least desirable trees and thinning and/or removing shrubs will help.
USE SHADE-TOLERANT GRASS: St. Augustine followed by zoysia are our two most shade-tolerant grasses. In cases where direct sunlight does not reach the ground during the day, an ornamental ground cover or simply mulch might be better.
CULTIVATE COMPACTED SOILS: Aerification with a machine that removes plugs of soil will help reduce compaction. Core aerifiers can be rented through various machinery rental companies.
IRRIGATE DEEPLY AND INFREQUENTLY: Avoid light frequent irrigations. Wait for signs of moisture stress before watering. Then irrigate to wet the soil to at least 6 inches. Most healthy turfgrasses need about 1 inch of water per week during active growth..
One last thing to consider is just letting the moss grow. I have seen examples where several homeowners have done this, and it looks very nice.