It can weaken and even destroy a lawn if not prevented or removed. Causes of thatch Factors favorable to thatch development include excessive growth and conditions unfavorable to the microorganisms that decompose decaying plant parts. Rapid and excessive growth is likely to produce a heavy thatch because plant material is being produced more rapidly than it can be decomposed. Grass clippings from mowing do not contribute to thatch. However, once a thatch layer has developed, clippings may speed its formation.
Thatch buildup varies among lawns.
Moderate to aggressively spreading species such as Kentucky bluegrass, zoysiagrass and bermudagrass have greater potential for thatch buildup than turf-type tall fescue and perennial ryegrass. Some lawns never develop a thatch layer, while others become thatch-bound within a few years after being established. The best lawn grasses are those that constantly reproduce new plants to renew the lawn. As old plants age and die, they decompose into fine-textured humus that becomes a part of the surface soil. Once thatch starts to form, conditions develop that may favor even more thatch.