If you cut your grass with a riding lawnmower or your lawn is a frequently used playground, most likely the soil is compacted and the turf would benefit from a good aeration. The purpose of aeration is to loosen the soil to improve both drainage and air flow. Grass roots breathe in oxygen and release carbon dioxide. This is entirely opposite of what leaves do.
Select the proper aerator for the job. Aerators with long, solid, pointed spikes add to the soil compaction problem. The spikes actually compress the soil as they enter the ground.
An aerator should remove cores of soil as it rolls across the lawn. Its hollow tubes should penetrate to a depth of three to four inches or more. You may need to weigh the aerator down with cement blocks to go that deep.
For maximum effectiveness, use the aerator in two directions. Run the aerator the length of the lawn, then across the width of the lawn. By using this two-directional method, you achieve better and more uniform distribution of cores.
To maximize the benefits of aeration, spread compost over the aerated area immediately afterward and rake the compost into the holes made by the aerator. Raking will not only help fill the holes but also will crush the plugs of soil made by the aerator.