I have moss totally taking over my backyard, which is filtered sun at best. Is the moss a result of the shade or a chemical imbalance in the soil, as a neighbor suggests? I am considering planting emerald zoysia in the next few weeks to replace the Bermuda. I would appreciate your addressing this problem. -- Ron

A: Turf frequently thins out when conditions for growing dense, healthy grass declines. This seems to be what's happening with your Bermuda, which needs full sun to thrive.

I see this all the time with Bermuda, because for the last 15 years or so Bermuda sod is planted (it's the cheapest) whenever a house is built. The homeowner plants a shade tree or two, or young existing trees grow bigger, and over the years the trees cast shade on the Bermuda. The grass thins out, and the moss grows.

So, to have a nice lawn, either the trees have to go or you have to change to a different grass.

Mosses are actually branched, threadlike plants that form a tangled, thick mat over the soil. It is not parasitic and it is spread by wind-blown spores. It can form a crust on the soil surface that reduces air and water movement into the soil.

It is more common in shady areas with infertile, acidic soil.

Cultural practices that favor turf growth 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 turf, the pH should be 5.8 to 6.5. If the soil is acidic, the results will tell you how much lime to apply.

- Improve drainage. Soils which stay moist because of poor drainage should be contoured so that water will drain off. In some cases, tile drainage may be needed.

- 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. Removing the least desirable trees and thinning or removing shrubs will also help. Areas surrounded by buildings and vegetation with limbs close to the ground may require considerable work to provide adequate air circulation and light penetration.

- Use shade-tolerant grass. You have the right idea in planting emerald zoysia since it is shade tolerant. Other zoysia varieties and St. Augustine will also work well. In cases where direct sunlight does not reach the ground during the day, an ornamental ground cover or simply mulch may be better suited to the site.

- 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. Drainage in fine-textured soils such as clay can be improved by cultivation and adding large amounts of organic matter and sand.

- Irrigate deeply and infrequently. Avoid light, frequent irrigations. Wait for signs of moisture stress such as the development of a bluish-gray, dull color before watering, then irrigate to wet the soil to at least 6 inches. Most healthy grasses need about 1 inch of water per week during active growth. If puddling occurs, stop irrigating and wait two to three hours for the water to soak into the soil before irrigating again. Repeat the cycle as needed until the soil is wet to the desired depth.

- Renovate. Generally, turf can be renovated if at least 50 percent of the area has the desired turf. If turf cover is less than 50 percent, then re-establishment will be necessary.

Chemicals can be applied but they are a temporary fix unless the growing conditions are improved. You can apply ferrous sulfate or similar products such as Scotts Moss Control Granules. There are others that are combined with a fertilizer, such as Scotts Lawn Fertilizer Plus Moss Control and Fertilome Lawn Food Plus Moss Control.

These products will do a better job if you rake or mow vertically to break up the layer of moss prior to or after chemical treatment.

Nonselective herbicides such as glyphosate (Roundup, other trade names), will kill moss, but will also kill -- or severely injure -- the grass.

One thing to consider is just letting the moss grow. I have seen examples where several homeowners have done this, and it looks nice. They figure, why fight it? Of course, when you try to grow moss, you can have a new problem: Birds love to use it to build their nests.

REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE IN RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.