In the mad rush to ensure your lawn is mowed, weeded, fertilized and irrigated, the need for aerating is often overlooked. But, as sod ages, the soil underneath can become so compacted, there is little or no pore space (small pockets of air held in the soil), making it difficult for grass roots to absorb water and nutrients. Before long, the lawn will deteriorate, becoming more susceptible to weeds and attack by insects and diseases.
Aeration involves the removal of small cores—or plugs of soil—which are then deposited on the surface (they’ll work their way into the grass within a month). The small holes that remain help to break up compacted areas and allow water and air to penetrate to the root zone.
The best time to aerate is early summer or early autumn, when the lawn is growing most actively. Unless freshly installed sod has been laid over compacted subsoil, as is often the case in new subdivisions, typically only mature lawns should need aerating.