Step 5. Increase Organic Matter and Microbes
Applying fertilizer will not help if your soil does not contain an adequate population of microbes; you need billions of these microscopic organisms per handful of soil. Your soil must contain 2- to 5-percent organic material to have a thriving microbe population. Microbes not only digest grass clippings, dead grass roots, and old stems, they make nutrients available to living grass plants. A top-dressing of compost mixed with topsoil followed by aeration will eventually incorporate some organic matter into the soil without disrupting the lawn.
When top-dressing your lawn, apply about 1-cubic yard, which is 100-pounds of a 40–60 mix of topsoil and compost, per 1,000-square feet. Topsoil is available from most nurseries and landscape centers. Be sure that it has a dark, rich, brown color and not diluted with lighter-colored sub-soils. Screen compost for 1/4- or 3/8-inch particles and it should be free of inorganic materials. Its moisture content should be 30- to 50-percent. Any drier, and the compost releases a lot of dust as it’s being worked; any wetter, and the material tends to clump and not mix well with soil.
You can obtain compost from several sources. Many towns make compost—from the leaves, grass, and brush that residents haul to the dump—available to residents at little or no cost. Compost is also available from nurseries and landscape centers, or you can make your own.