Dethatching, also called power raking, removes thatch: the layer of dead stems, roots, and runners that builds up between the green blades of grass and the soil. A thin layer is normal and harmless. When it grows thicker than about half an inch, it begins to shed water, hold moisture against the crowns of the grass, and harbor insects.
How it is done
A dethatcher uses rotating tines to cut down through the thatch layer and lift it to the surface. The crew then picks up the debris and takes it away, so there is nothing left for you to rake, bag, or haul.
Does your lawn need it
Not every lawn does. A quick check is to cut a small plug from the lawn and measure the spongy brown layer above the soil. If it is less than about half an inch, the lawn does not need to be dethatched, and core aeration is usually the better service.
When
Dethatching is done while the grass is actively growing and can recover, in spring or early fall. It is hard on a lawn in summer heat and is not scheduled then.