Thatch is a dark brown layer of dead and living shoots, stems and roots that develops between the zone of green vegetation and the soil surface. Thatch consists of a loosely interwoven collection of plant matter that imparts sponginess to the turf. Excessive thatch build-up can contribute to turf decline and in some instances, stand loss. Thatch often desiccates and is more prone to insect and disease invasion.
The thatch layer also ties up nutrients and pesticides, harbors insects and disease, and restricts normal moisture penetration to the soil. Thatch reduces cold and drought tolerance. Thatch makes mowing very difficult. As thatch builds up, mowing heights actually increase above the soil line and the turf becomes very spongy allowing the mower to sink into the turf and scalp the lawn.
St Augustine, Bermuda grass, and Zoysia grass tend to experience excessive thatch build-up; Centipede grass also forms thatch, but at a slower rate; unless it is over fertilized. Improper mechanical practices (Core Aeration) can also result in thatch accumulation. Over fertilizing, over watering, and infrequent mowing are the biggest contributors to a thatch problem.