Core aeration is one of the most important things you can have done to your lawn each season. Warm season grasses such as bermuda, zoysia, and centipede should be core aerated after spring green-up. Cool season grasses like fescue should be aerated in conjunction with seeding in the fall. Core aeration is important to the health and vigor of your lawn for several reasons: The first is the reduction of soil compaction, and the second is the increase of air, water and nutrients to the roots of your grass.
Relief of soil compaction:
Southeastern clay soils will become very hard and compact over time. Compact soil severely reduces the ability of grass roots to expand and take up water and nutrients. The "coring" process created by the aerating machine pulls 1/2 inch diameter cores of soil from your lawn and deposits them on the soil surface. These cores will break apart within a week or two, and the holes made by the coring process will gradually fill in. Overall, what happens is the top 2 to 2 1/2 inches of soil is loosened up allowing roots to grow outward and deeper. As the cores break apart, they help to break down thatch and other debris that accumulates at the soil surface and interferes with fertilizer uptake and preventive weed controls.
Increased air, water and nutrient uptake:
It is very difficult for water and nutrients to penetrate compact clay soil. If the majority of the water and nutrient material is located close to the surface of the ground, the roots of your grass will also grow close to the surface. This makes the roots susceptible to damage from heat stress, foot traffic, freezes and wind chill. The deeper and more extensive the grass root systems are, the thicker and more healthy your lawn will be. CORE aeration allows more of the water and nutrients to penetrate deeper into the soil. SPIKE aeration does not accomplish this nearly as well. Spike aerators simply poke holes in the lawn, but do not remove the cores.
The ability of your grass to take up and process water and nutrients is directly related to how deep, extensive, and strong the root systems are. The stronger the roots, the healthier, thicker, and greener your lawn will be. Strong healthy roots also help your grass to naturally fight off diseases such as Dollar Spot Fungus. Dollar Spot is most evident in lawns that are stressed and have weak roots, and is often first seen around the edges of the lawn by sidewalks and driveways. This is due to the increased soil temperatures from the concrete and asphalt which compact the soil and damage roots. Heavy core aeration each season in these areas improves the strength of the roots in these areas, and makes these areas less susceptible to damage.
Even if your lawn is lush, thick and green, you should still core aerate it every season. Aeration is more useful as a preventative measure than a corrective one. If your soil never gets compact, then you never have to worry about the problems that arise from compaction.