Aeration involves perforating the soil with small holes to allow air, water and nutrients to penetrate the grass roots. This helps the roots grow deeply and produce a stronger, more vigorous lawn. Clay-heavy soils need to be aerated frequently, about once a year, since the soil tends to be dense and compact. Sandy soils can be aerated every two years. The excavated soil plugs should be allowed to dry and then broken up to give your lawn a uniform, clean appearance. Break them up by running them over with a lawn mower or pounding them with the back of a rake. Your lawn will thank you for letting it breathe again.