While they do lots of good things for soil structure in terms of creating air spaces, earthworms' greatest role is as a major producer of natural fertilizer. As they go about their business in the soil under your lawn they excrete their weight in castings every day. Worm castings are an absolutely wonderful fertilizer, providing nutrients in a form grass plants can use. In a 1000 sq. ft. area for example, at a density of only five worms per cubic foot (considered a low population), your earthworms will give you over 150 pounds--about 1/3 pound per worm--of top-grade fertilizer during each growing season. This fertilizer contains the key plant nutrients--nitrogen, phosphorus, and potassium--plus many of the essential micronutrients plants need to grow and remain healthy. Dead earthworms are also very rich in nitrogen. Earthworm castings offer the equivalent of about ½ to1 pound of nitrogen per 1000 sq. ft. per year, or over 25% of the total fertilizer needs of the turfgrass.

Worms not only produce this valuable fertilizer, they also spread it evenly throughout the top 12 inches of the soil. In many cases they travel much deeper, sometimes as far down as 6 feet. A well-managed soil rich in organic matter can easily support 25 worms per cubic foot, which, in that same 1000-square-foot area, means at least 800 pounds of fertilizer. That amounts to a lot more than 2 pounds of nitrogen for each 1000 square foot, all courtesy of Mother Nature.

If you decide to take advantage of the work that earthworms do in your lawn, that has implications as to whether you choose quick acting or slow acting fertilizer. Quick acting nitrogen fertilizer can make the soil more acidic. Research shows that when enough fertilizer is added to a lawn to cause the soil to become more acidic, thatch accumulation goes up and earthworm populations go down, every time. It follows that if you are trying to attract worms to help you with fertilizing the lawn, then you will avoid routine use of quick-acting fertilizers. These products do have their place, but not as main meals for turf where earthworms are invited guests.

The real key to keeping your worm population high is adding lots of organic material to your lawn every single year without fail. The process is described in the lawn grass mulching section; click here to go there.