Moss Versus Algae

• Both moss and algae are green organisms that can grow where grass does not. However, they are different in appearance and require different treatment methods. Moss produces a soft mat composed of threadlike stems. It is most likely to grow in humid, shady areas of infertile, acidic, compacted and poorly-drained soils. Algae, on the other hand, prefers full sunlight and produces a green, scummy substance on moist soil that dries to a tough black crust. Other conditions that favor algae include compacted, highly fertile soils.
  
  

Reduce Favorable Conditions for Algae

• To reduce conditions that favor algae, improve lawn drainage, increase light penetration and air movement and loosen compacted soils. Contour or trench poorly-drained areas, and add sand or soil to increase elevation in low-lying areas, which will move water away and allow excessively wet areas to dry. Increase light penetration and air movement by trimming lower tree branches or removing unwanted, shady plants. To loosen compacted soil, cultivate or core the top 2 to 4 inches. Deep tilling is usually not necessary.
  
  

Chemical Treatments and Fertilizers

• Chemical treatments are not effective for algae, and the wrong ones -- such as nonselective herbicides -- will just kill the grass and other desirable plants. Conduct a soil test; kits are available at most gardening stores. These tests measure several characteristics of soil, including acidity, and provide a chart indicating what common additives or fertilizers can be used to correct the situation. Hydrated lime is an appropriate additive for acidic soil affected by algae; follow instructions as to how much to add. Copper sulfate can also be used to control algae at a rate of 3 to 5 oz. per 3 gallons over a 1,000 square foot area.
  
  

Choose Appropriate Grass

• Choosing the right turf grass for your yard will avoid many problems, including those created by algae overgrowth. St. Augustine or fescue are good choices for partially shaded areas while warm-season grasses -- especially Bermuda grass -- will just create thin and poorly-growing areas. For lawns with heavy shade and trees, try ground covers or mulch instead of grass.