According to the Lawn Institute, thatch is produced more by the misuse of strong fertilizers and pesticides than by clippings alone. Thatch is a layer of dried grass clippings that builds up on the soil surface. A healthy soil biota can easily decompose the normal amount of clippings to keep the thatch layer from building up. But earthworms, which perform much of this task, are especially vulnerable to popular lawn chemicals. For a healthy lawn, mow frequently.
Short clippings are tender and rot quickly.
Adjust the pH to 6.5 to 7.5, the range favored by most grass species. When planting trees and shrubs, the more compost, peat moss and other amendments you can mix into the ground, the better. In the early 1970s, Carl Whitcomb, a researcher at Oklahoma State University, disproved this oft-repeated advice. The amendments seemed to encourage roots to stay in the vicinity of their planting holes and not grow out into the unamended soil, leading to stunted root systems. Whitcomb concluded that it's best to let the roots begin to grow in the nativ soil right away and to use organic matter on the surface as a mulch, rather than mixing it with the soil.