Controlling thatch is one of the most important – and most overlooked – parts of lawn care. Thatch is simply the layer of dead grass, roots, and debris that accumulates between the soil surface and the green grass blades above. Over time, it forms a thick mat, hindering water and air from reaching the soil and providing an environment that can encourage pests and diseases. Dethatching can help prevent these problems. Almost every lawn needs dethatching about once a year, or whenever the thatch reaches a thickness of about 1/2 inch (1.2cm). To check, just work your fingers into the grass and note the depth of the thatch layer. Dethatch cool-season grasses in autumn, warm-season types in late winter, early spring.