After a year of a being trampled upon by various activities that tend to pack the soil, the grass roots need a breath of fresh air (oxygen) for respiration that only proper aeration can provide. This helps the root systems better establish themselves for the coming winter. Aeration should take place approximately two weeks before applying the year's final fertilizer, or five to six weeks before the first frost.
The most effective aerator has hollow tines that penetrate the ground and remove plugs of soil that are expelled as each successive hole is made, leaving a vent for true aeration. Although a freshly aerated lawn appears a bit unsightly with numerous plugs laying all over it, they will eventually dissolve, returning nutrients to the soil for use by the grass.The unsightly appearance can be reduced and the plug dissolving process speeded up by mowing with a low-cutting blade once the plugs are dry.
Be sure to remove the grass clipping bag and then mow the entire lawn in a left-to-right pattern, followed by an up-and-down pattern to assure even break-up and spreading of the aeration plugs. After mowing, watering the lawn further helps dissolve the aeration plugs.