Thatch is a tightly intermingled layer of partially decomposed stems and roots of grass that develops between the actively growing grass and the soil surface. Thatch slows grass growth by restricting the movement of water, air, and nutrients in the soil. Thatch is normal in a lawn, but when it is thicker than 1/2 inch, the lawn begins to suffer. As the layer accumulates, the grass roots grow in the thatch instead of down into the soil. Thatch accumulation is encouraged by overly vigorous grass growth caused by excessive fertilization and frequent watering.
To reduce the thatch and increase the lawn''s vigor, power rake or dethatch the lawn. Dethatch cool-season grasses in the fall and warm-season grasses in late spring or early summer. Avoid dethatching while new growth is turning green. Machines for the job can be rented, or hire a contractor. First, mow the lawn as short as possible. Go over it one to three times with the dethatcher. Rake up the debris, fertilize, and water to assist the lawn''s recovery.