Thatch is an accumulation of dead and living plant parts located at the soil surface, just below the grass. Thatch creates a sponge like barrier, trapping vital moisture and nutrients up on the surface away from the reach of your roots. This causes an unhealthy, unnatural state, with roots that grow up on the surface and in the thatch, instead of down deep in your soil where vital moisture and nutrients are held. Roots cannot survive long on the surface, and when they die they add to even more thatch. Thatch is also a breeding area for turf damaging insects and contributes to the growth and spread of fungi which causes lawn disease. Think of it as a wet kitchen sponge harboring all kinds of bacteria. Thatch weakens the health of your lawn, making it more susceptible to damage from heat stress, insects, and diseases.