Worms do it for you, but they can only do so much. To make sure your soil has access to air, water and other vital resources, aeration is necessary twice a year. This process also leaves nutrient-rich pellets on the surface of the soil, which will further condition your soil as they decompose and reenter the topsoil
The aeration process of pulling plugs from the lawn provides much needed oxygen or "air" to the roots of the lawn. This also allows water to get to the roots to provide that strong root base, so your lawn will stay healthy for all four seasons. * Best done in spring or fall.