Dethatching if you look beneath the grass and there is a layer of grass that seems to be all matted together, you may need to dethatch. Thatch is a layer of dead stems, roots and clippings between the soil's surface and the green vegetation. Thatch can deprive your lawn of the vital nutrients it needs to be healthy. A thatch layer of one-half inch or more also keeps water and air from entering the grass roots and provides the perfect breeding environment for insects and diseae.

Aeration it makes spaces in the soil the roots to get air, water, and nutrients. Post-aeration fertilization, amendment, and watering encourage deeper root growth. With lots of little holes all over it, the lawn soaks up water more efficiently, too, so it's a good way to reduce water loss on slopes.