Core-type aeration is recommended to relieve soil compaction. Compacted soil does not have the proper amount of oxygen for deep rooting of the grass, and will result in the grass thinning, or showing excess wear and tear from what would otherwise be normal use. Additionally, in dry periods, compacted soil does not absorb water properly and will often actually repel irrigation water.

Soil compaction can result from a number of causes. Pedestrian or equipment traffic, heavy organic soil in poorly drained areas, trees depleting the organic matter in the soil causing it to collapse, and fill soil with heavy clay content can all result in compacted soil.

Core type aeration machines can be rented at many equipment rental stores. When aerating a lawn, be sure to use a machine that will remove a core of soil and NOT simply punch holes in the ground. Spikes punched into the soil do not relieve compaction; in fact they increase compaction. The soil should be wet before aerating, so the soil core will be removed intact, and the yard should be covered twice, once north and south, and a second time, east and west. Leave the removed cores where they fall. They will disappear after a few days.

Aeration can also be beneficial in helping to accelerate thatch decomposition by increasing the air circulation to the thatch layer.