What Is Aeration?

Lawn aeration opens up the soil under the existing turf grass to introduce air, which is essential to healthy grass plant roots, into it. This helps reduce compaction of the soil, which is a chronic problem in American residential landscapes where the air has been compressed out of the soil by foot traffic, heavy rains, heavy equipment at building sites, and loss of organic matter in the soil over time. Grass roots struggle to penetrate this compressed soil in search of moisture and nutrients. Lawns growing in compacted soil are almost always poor looking and high maintenance.

Obviously it is more difficult to introduce air into the soil in established lawns than in garden beds where the soil can be turned with a tiller, shovel or trowel before plants are planted. The most direct aerating method is to punch holes or slice crevices into the turf. An indirect method is to topdress the lawn with organic matter that will gradually be incorporated into the soil beneath and improve its texture to reduce compaction. A thin layer of topsoil, compost, municipal sludge or similar material rich in humus or a layer of finely shredded leaves deposited by a mulching lawn mower helps the soil retain air.

All about Compaction

Soil compaction is inevitable. Simply walking behind the lawnmower 20 to 30 times a season takes its toll. The pressure of one single footstep of a 150 pound person impacts soil as deep as 15 inches. Riding mowers, parked cars, construction equipment, kids' play--even heavy rain-- cause even more pressure.
Compacted soil is bad for lawns. Grass roots need easy access to water, air, and nutrients in the soil to be able to metabolize energy and grow vigorously. Soil compaction destroys the tiny pockets in the structure of the soil that hold air to stimulate root growth. Grass roots are also stunted and stressed because they can't penetrate the soil. Lack of air spaces also causes soil to drain poorly
Compacted soil is bad for soil life. It hinders the circulation of earthworms and the lack of air stiffles the activity of micro-organisms which enrich the soil. Compacted soil promotes the buildup of thatch as grass roots, starved for air, migrate and accumulate near the surface of the soil, matting and obstructing the rapid decomposition of clippings.

Core Aeration Fights Compaction

One way to dramatically reduce the normal compaction of the soil your grass grows in is to mechanically punch holes in the turf to introduce oxygen below the soil surface. Use either a power-driven core aerating machine or a hand core aerating tool. These devices have hollow tines which penetrate 2 or 3 inches below the soil surface. When they are withdrawn, they pull out a core of soil about ½ inch in diameter and from 2 to 3 inches long, which they deposit on the lawn surface. They leave a hole in the turf at each spot.
The oxygen that enters the soil through the aerating holes reverses any decline of soil health almost immediately. It stimulates the activity of soil microorganisms that busy themselves with reproduction and feeding which brings the soil alive. Earthworms move more freely through the soil, leaving their castings that provide nutrition to grass roots. Better able to find and take up soil nutrients, grass roots now begin to grow vigorously and vertically, finding it much easier to penetrate the soil.
Aeration also breaks down grass roots that spread laterally and cause thatch problems near the soil surface. As the little cores of soil left on the turf begin to disintegrate, the microorganisms in them stimulate decomposition of the accumulated thatch to a layer that is an acceptable ¼ inch or less. Normally thatch buildup occurs in three to five year cycles, so aerating the lawn every two or three years controls thatch and prevents it from accumulating.