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 vs. power raking? Pro tips on what’s best for your lawn
