The key to any successful organic lawn program is the soil. It must be alive with wide variety of beneficial microorganisms and bugs. Beneficial microbes both feed and protect the plants from other, disease-causing bacteria and fungi. All the you have to do is feed the beneficial microbes and let them do their work.
TESTING YOUR SOIL
The first step before implementing any new landscaping should always be to take a soil test. A soil test will tell you exactly what your lawn or garden needs so you can add only those nutrients that are necessary. You send a sample of your soil to a soil testing laboratory, and they send a report on the chemistry of your soil with specific recommendations of what types of fertilizers and nutrients you need.
For example, soil with a calcium deficiency can be top-dressed with gypsum; and soil low in magnesium might need a healthy dose of the mineral langbeinite. You will need to dig up samples from several different areas of your lawn (2 cups of soil total), and mail them off to a lab to be analyzed.
We here at HowToOrganics.com suggest using Logan Labs (http://www.loganlabs.com) as they quick and accurate. Though there are many other testing companies to choose from.
To assess how good (or bad) your soil is, you can conduct a simple test. Use a trowel or shovel to cut out a small piece of sod at least 4" deep. Now take a close look at what's both above and below ground. Is the soil crumbly and soft? Does it contain a dense patch of healthy grass blades and maybe a worm or two? Those are the characteristics of healthy turf.
If the sod sample is dry or compacted, the roots may appear weak and shallow. A dense accumulation of dead roots, stems and partially decayed organic matter at the base of the grass is called thatch. Normally this material gets re-incorporated into the soil by microorganisms and earthworms. In poor and/or biologically inactive soils, this organic matter accumulates at the soil surface and creates an ideal environment for disease. Thatch can be removed by vigorous raking or by using a power dethatching tool. Thatch is rarely a problem if you have fertile, biologically-active soil, and your lawn is maintained according to the practices recommended for natural lawn care.
Grass roots and soil microorganisms prefer loose, airy soils. If your lawn has become compacted from heavy power mowers or from foot traffic, spring is a good time to aerate. The objective is to open up passageways in the soil for air, water, nutrients and soil life. Use a manual or power aerating tool. Apply fertilizer or lime (if needed) right after aerating, while the soil is exposed.
But be sure to conduct a soil test to check the pH of your soil. Most varieties of grass prefer a slightly acid to neutral pH (6.5-7.0) A simple soil test will tell you if your soil needs an application of lime to make it more neutral, or sulfur to make it more acidic.