“I would like my lawn to look better this year. Should I start the growing season off by both power raking and core aerating?”
—Layla Thompson, Skokie
I recommend using core aeration as an annual practice for lawns instead of power raking, which most everyone seems to do.
Core aeration improves the lawn’s health and vigor by breaking up soil compaction, which improves water drainage, nutrient absorption and air circulation to the roots. A stronger root system will promote a better-looking and healthier lawn.
Combining core aeration with proper watering, mowing and fertilizing will help keep your lawn growing strong and better able to withstand stress and reduce weed problems. Lawn aeration will also provide an opportunity to over-seed if any areas of your yard are thin.
The best time to aerate cool-season grasses like Kentucky bluegrass that make up most Chicago-area lawns is in spring and fall, when the grasses are actively growing. Weather conditions are different from year to year, but April or May and September or October are generally good months to schedule aeration. I prefer the spring window for core aeration. For lawns that are heavily used, it might be beneficial to aerate twice per year.
Core aeration is done with a machine that removes small plugs of grass and soil from the ground. You can rent a core aerator or hire a company to do the work for you. The machines are heavy and need to be transported in the back of a truck or trailer. You will need a ramp, which should be available at the rental store to drive the machine on and off the truck.
You will get the best results if the soil is moist but not wet. The machine will not be able to pull good cores if the ground is very dry and hard.
Flag any sprinkler heads, light fixtures, valve boxes and other hidden items before aerating, so that you can avoid damaging them or the machine.
If your lawn has been recently sodded, then make sure it is well rooted in before aerating, or the machine will pull up the sod. A general rule would be to wait a year after sodding before beginning a core aeration program. Lawns sodded last summer should be OK to aerate now.
Afterward, it is best to leave the cores on top of the lawn and let them naturally break down over a couple of weeks.
Lawn aeration will also help to decrease the buildup of thatch, a layer of organic matter that has not decomposed at the top of the soil. This can occur when there is excess grass growth caused by over-fertilization and light, frequent irrigation.
If this layer gets too thick, it will absorb moisture and encourage shallow rooting of the grass, making it more prone to drought stress and less able to absorb nutrients. Grub control will be less effective when there is excessive thatch in a lawn.
Power raking can be beneficial for lawns that have excess thatch (more than 3/4-inch thick) buildup.
The lawn will look tidier in the short term once the plant debris generated by the power raking is cleaned up, so go ahead and power rake before aerating if this is important to you.
Once the lawn greens up and starts growing, you will not notice if you skip the power raking.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.
