Thatch

1. an intertwined layer of dead and living roots, stems and blades of grass plants. It holds water, pesticides and fertilizer like a sponge, preventing them from reaching the roots.

A thatch layer that is more than 1" thick may need core aeration spacing as close as every 3" to be effective.
Source: http://hflp.sdstate.edu/Pestalrt/alert809.htm



An example of excessive thatch buildup.
Source: http://hflp.sdstate.edu/Pestalrt/alert809.htm