Thatch is a natural occurring layer of accumulated grass clippings, stems, roots and other decomposing matter found between growing grass and the soil under it often creating the spongy feel when walking on a thatchy lawn.
Thatch develops when high maintenance lawns produce organic waste matter quicker than it can be broken down. A high-maintenance lawn tends to develop thatch more quickly than a low-maintenance one. Compaction, unbalanced fertilization, overuse of chemical sprays and improper care can also increase thatch growth.
When thatch is half inch or less it can improve overall turf resiliency when faced with heavy use, drought or high heat because it will hold in extra moisture and shield the soil from the sun. When thatch gets closer to an inch or thicker it impedes the ability of water, fertilizer, air and other nutrients to get to the roots. If thatch dries out it will decrease the drought resistance of the grass, if it stays wet fungus and other diseases may grow.
Prevent thatch by proper care and management by balanced fertilizing, aerating if needed, and mowing regularly. Growing a low maintenance lawn using alternatives to bluegrass like Natures Prairie Turf ™, Enviroturf™, 90-10, Cowboy Turf™ or other alternative grasses will alleviate the thatch issue as well.