Thatch is a collection of grass roots, rhizomes, stems, and other grass matter on the surface of the soil. A small amount of thatch is good for your lawn as it acts like a blanket to keep the soil and grass roots warm, and it also helps retain the water. However, if thatch builds up to a layer about 3/4 - 1 inch thick it could cause problems (see picture above - the light brown section directly under the grass is the thatch layer). Some pest insects that feed on your grass, such as chinch bugs and sod webworms, will live in the thatch. It can also promote disease-causing fungi, such as Dollar Spot and Brown Patch. If it gets to this point, it is a good idea to dethatch. This will lower the thatch layer to a level where it will once again be beneficial to your lawn. Overseeding is recommended after this service.