When should I dethatch my grass?

Thatch is an accumulation of partially decomposed and undecomposed plant material at the soil surface. Thatch accumulation of less than one-half inch can be beneficial. Thatch accumulations of more than one inch are harmful. Remove thatch whenever it accumulates to more than one inch, but thatch is a symptom, not a disease. Thatch accumulated when something interfered with the microbial breakdown of plant material. If you have a thatch problem, it is usually due to soil compaction, poor drainage, or low soil pH. Alleviate the problem and the thatch will not re-occur.