What is core aeration and what does it do? Core aeration is a mechanical process that actually opens up the surface of the lawn to expose 4 times the surface area with out destroying the turf grass. This allows fertilizer, water and oxygen to get to the roots where healthy grass originates. A core aerator is a machine with hollow tines that penetrates the soil to a depth of 4 to 6 inches and actually pulls a plug of soil out and throws it on the surface of the lawn. The tines are spaced 3 to 4 inches apart and do a good job of pulling the plugs out on moderately moist lawns. In order to achieve best results the machine should be run over the entire lawn area in 3 to 4 different directions to really open the lawn surface. On heavily compacted turf such as sports fields up to 8 passes may be needed to get the desired results.
Core Aeration is effective for all turf grass species. Both cool season (i.e. Kentucky bluegrass) and warm season grasses (i.e. Bermuda grass) can be greatly improved by a regular use of aeration. When talking about lawn care the use of aeration should be a regular part of cultural care just like fertilization, irrigation, and weed control, not just a one time fix.
On heavy soils the ground can be compacted, especially clay soil, from heavy foot traffic or even heavy rain. In areas where the soil has a high clay content, compaction and thatch buildup is more prevalent and aeration should be done twice a year. In areas of more sandy or loamy soils, annual aeration will result in continued healthy lawns and improved irrigation and fertilizing efficiency. The more compacted the soil is the less space between the soil particles for air spaces.
Space between the soil particles is very important for several reasons. First these air spaces allow for the exchange of gases in the soil. If the soil is too compacted the gases manufactured by the plant can not escape and are trapped in the soil leading to poor growing condition. The more compacted the soil is the harder it is for water and nutrients to move down into the root zone. Without adequate moisture and nutrients the turf grass will weaken and die. Most important of all is that the roots of the turf grass do not actually grow in the soil they grow in the air spaces around the soil the less air spaces the less roots. Core aeration helps alleviate compaction and opens the soil up to help make the soil more able to accomplish these tasks.
Depending on the turf conditions, visual results may or may not be immediate from a single aeration. Subterranean root growth and overall health and stress tolerance will however begin to improve almost at once. Even in the toughest conditions aeration in combination with an appropriate fertilizing, irrigation and weed control program will show dramatic visual results in the second year after a second or third aeration.
The best time for aeration for cool season grass is in the early spring March through May and in the fall August through November. Cool season grasses would be bluegrass, bentgrass, rye grass and fine leaf and tall fescue. Warm season grasses should be aerated May through July. Warm season grasses are Bermuda, Buffalo, St. Augustine, and Zoysia .
Once the the lawn as been aerated, pre-emergent herbicide is best applied after aeration to reduce the chance of weed invasion in the yard while grass is spreading to the cored holes. Do not apply pre-emergent herbicide if you intend to over seed. Fertilizing will also be more effective at this time. Never aerate in times of high heat or drought. The plugs that are left will break up as you mow the lawn and actually work as a top dressing throwing the soil on top and helping to break down the thatch layer by spreading the micro organisms in the soil on top of the thatch layer.
To really appreciate just what core aeration does for the plant a simple test can show you the benefit. After 3 to 4 weeks go out on the lawn with a spade and dig up a square block of soil about 8 inches by 8 inches about 10 inches deep. Next take a large knife and slice straight down through the soil over the center of one of the aeration holes and pull the soil apart and look at the two sides. You will find the aeration hole is packed with new healthy white roots ready to provide and store nutrients and moisture for the turf grass plants.