A soil that contains the desirable 3% to 5% organic matter in the top 8 to 12 inches will have a very active microbial population, assuming there is sufficient air and water available (the soil must not be seriously compacted).

Those microbes do many good things including decompose thatch, control diseases and pest insects, and produce nutrients for consumption by the grass plants. One of those nutrients is nitrogen. A healthy microbial population working in a soil with sufficient organic matter will produce ½ to 1 pound of nitrogen per 1000 square feet of lawn each season, representing about 25% of your lawn's nitrogen needs. As with the earthworms, if you choose to use a quick acting nitrogen lawn fertilizer, you will make the soil more acid and greatly reduce the population of these valuable microbes, eliminating their contribution of nitrogen. Then you have to make up the difference.

As with the earthworms, the key to having a healthy population of microbes is to add organic material to your lawn’s soil year in and year out. The Lawn Grass Mulching section tells you how to do that. Click here.

Questions and Answers

Q - Where can I buy benificial soil bacteria?

A - You can buy a product called Plant Growth Activator.  It contains billions of beneficial soil microbes.  English Gardens has them.  Then follow the instructions.