Lawn thatch is composed of a tightly intermingled layer of stems, leaves and grass roots, which accumulates between the vegetation and the soil. Too much thatch increases the turf's susceptibility to lawn diseases, reduces its tolerance to drought, cold, and heat stress; and hinders the movement of air, water, fertilizers, and nutrients into the soil. In severe cases roots of the grass will not grow into the soil but only take root in the thatch layer making the turf susceptible to drought and heat stress.
Thatch will accumulate in a lawn if the production of dead material exceeds the ability of the microorganisms in the soil to break down the organic matter. Thatch build-up occurs in lawns that have "dead soils" and is caused by an absence of beneficial microbial activity. Thatch buildup happens if there is poor soil aeration and drainage, improper lawn watering practices (usually too much water or too frequent water), cold temperatures, the use of chemical pesticides, and the use of synthetic fertilizers.. When a lawn's thatch layer is greater than 3/4 of an inch thick it may need to be mechanically removed.
Note: 99%+ of lawns DO NOT need to have the thatch removed via power raking or vertical raking. Please contact your local lawn care expert before scheduling a power rake. If a lawn is building thatch faster than the microbes can break it down, this indicates that the lawn is lacking beneficial microbes. The cure to a thatch problem is not physical removal of the thatch, but by managing thatch in a lawn by stopping the improper cultural practice that is killing microbes in the soil.
More than 1/2 inch of thatch can be a problem for the lawn.
Managing thatch in a lawn is easy. Start by stimulating beneficial microbial activity by using proper watering practices, mowing practices, aeration and fertilization.
Power raking is a tool that can be used as a last resort to manage a major thatch problem, but power raking is not the cure of the thatch problem.