Thatch buildup can be a problem in some turf, especially bluegrass. The following is more information.
Excessive thatch accumulation is a problem on many turfgrass sites. Thatch is a layer of organic material consisting of tightly intermingled, living and dead plant tissues derived from crowns, stems, and roots. These parts of a turfgrass plant have a relatively high lignin content. Lignin is an organic compound that is highly resistant to microbial breakdown. Accumulation of a thatch layer occurs when the production of organic material (such as lignin) exceeds the rate of decomposition within the zone between green leaf tissue and the soil surface.
To assess thatch accumulation, remove a section of grass and soil from the turf using a knife, soil probe or shovel, and measure the depth of accumulated thatch. Depths greater than 1/2 inch indicate that corrective measures may be needed to reduce the thatch layer. Measurements from several locations through the turf area are needed because of the variable nature of thatch.
A thatch depth less than 1/2 inch can be beneficial because it improves turf resiliency and wear tolerance, and insulates the soil from extremes in air temperature. However, as thatch accumulates beyond 1/2 inch, the disadvantages begin to outweigh the benefits. Excessive accumulation tends to increase the susceptibility of a turf to heat, cold, and drought stress. Localized dry spots, scalping, disease, and insects may also be enhanced by excessive thatch. Such difficulties may develop as excessive thatch accumulates because the turfgrass plants will tend to have a greater portion of their crowns, rhizomes, and roots growing within the thatch rather than the soil. A weakened, poorly rooted turf is also more prone to injury and requires increased management.
Turfgrass species differ in their tendency to accumulate thatch because they have different growth rates, growth habits, and percentage of various cell wall components (Table 1). Lignin is one cell wall component that resists microbial breakdown. Vigorous species and cultivars with high lignin content accumulate thatch more readily than those with slower growth rates and lower lignin content.
Information from "Thatch Management in Turf" Rutgers University Extension Factsheet FS740 by James A. Murphy, Ph.D., Extension Specialist in Turfgrass Mamagement