What is Aeration?
Aeration is the process of making your lawn more accessible to air, water and nutrients. Aerated lawns are more vigorous and healthy than non-aerated ones and they show it.

The Process of Aerating a Lawn
Aeration is accomplished by operating a machine (aerator) over the surface of the lawn. Aerators come in a variety of configurations. The most common is a core type unit that removes small plugs from the turf. Core aerators have a minimum penetration of 2 ½ inches and remove plugs from anywhere ½ to ¾ inch in diameter. Spiking units push small tines into the soil. The process forms holes in the turf without removing soil plugs. A third type, slicing aerators, literally slice through the soil creating openings.
The Result:
Aeration opens up the soil to air, water and nutrients. The openings allow air penetration and better water movement, and give plant roots a place to stretch out and grow to become more vigorous and dense. Aerated lawns are less susceptible to disease and thatch buildup. And in some cases, the process can even resolve small thatch problems. In addition, aeration reduces soil compaction and water runoff and increases turf tolerance to drought.

Timing:
Aeration can be done anytime during the growing season. How many times your lawn needs aerating depends on its soil compaction. The two most popular times to aerate are spring and fall. Spring aeration gives grass plants a little extra boast and provides faster greening: fall aeration helps strengthen underground root systems while providing an excellent bed for over seeding.
The Results of Thatching
General Observations: Aeration is a natural process that has no ill side effects. Even small plugs left behind by core type aerators are beneficial. In the process of breaking down, they deposit a light coating of topdressing that helps decompose thatch accumulated sat the base of grass plants