A healthy lawn involves more than a weekly mowing. Plant roots need oxygen in the soil to grow. When we walk on, play on, mow, or do other activities on a lawn, the soil gets compacted, which reduces the amount of pore space in a soil. This limits the amount of air available to the grass plants. Compacted soils become a barrier to root growth. Fewer roots mean the grass loses capacity to absorb water and nutrients, becoming weaker with less top growth and more susceptible to insects and disease. To counteract compaction, we core aerate the lawn.
Aerating removes small soil plugs or cores from a lawn. Most aeration is most effective with a machine with hollow tines that extract 1/2- to 3/4-inch diameter cores. These end up on the lawn after aerating. The holes are usually 1-6 inches deep and 2-6 inches apart. Aerators with solid tines push the cores into the soil rather than pulling them up. This contributes to more compaction. Hand aerators and garden shoes with spikes on them are ineffective.
The benefits of core aerating are many. Besides increasing water, nutrient and oxygen movement into a soil, it also improves root development and increases the activity of soil microorganisms that decompose and reduce thatch. Increased water infiltration reduces run-off from irrigation or rainfall. This decreases fertilizer and pesticide run-off into streams and drainages.
To test if core aeration is necessary, dig up a 6-inch cube of lawn and look at the soil and roots. If the roots are only in the first 1–2 inches of soil, core aeration is a good idea. If the layer of thatch, which looks like a pad at the top of the soil under the grass blades, is more than 1/2-inch, it is time to aerate. When your lawn is heavily used and is starting to look thin, you may want to aerate. Heavy clay soils need aeration more frequently than sandy soils, perhaps once each year.
To aerate properly, the soil should be moist, but not wet. Deep water (six inches) a couple of days prior to aerating. Mark sprinklers clearly. Aerate the lawn in two different directions to improve coverage. Avoid tree roots. Leave the cores on the lawn to provide organic matter back to the soil. Apply compost or top dressing over the lawn 1/4 inch deep and rake into the holes. Water well when finished.
Healthy grass plants mean a good-looking lawn.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.