An established lawn generally has some
thatch buildup. Pieces of stems, roots, rhizomes, stolons, and debris
are slow to decay because they have high cellulose content and therefore
build up in a layer between the grass blades and the soil surface.
This makes it difficult for water to penetrate the soil surface and
reach the roots, causing patches of dead grass or thin areas.
Where thatch buildup is a problem, the soil must be dethatched with
a dethatcher or verticutter, which is a mower with vertical blades.
Dethatchers can be rented from equipment companies. The dethatcher
cuts through the thatch layer leaving the thatch debris on top of
the lawn and leaves grooves in the soil so that new seed can be planted.
Aerating the soil
After dethatching, rake up the debris and then aerate the
soil. An aerator pulls cores of soil from the surface, loosening
it and allowing moisture and oxygen to penetrate.
Next step to overseeding your lawn
Seed, fertilize, and irrigate