Where to Start: Aerate
Core aeration, removing 3- to 4-inch-long plugs of soil, is usually done in the fall when the chance of encouraging weed seeds is lower. But if you plan to use preemergent weed control with the first dose of spring fertilizer, aerating now is a good way to loosen compacted soil so that oxygen and fertilizer get down to the roots, says Nick Christians of Iowa State University's Department of Horticulture. You can manually aerate small areas with a foot-powered core extractor, but consider renting a gas-powered one for about $60 a day to handle bigger lawns.
Shown: For larger lawns TOH landscape contractor Roger Cook uses a walk-behind aerator that pulls out 2½-to 3-inch-deep soil plugs, which will break down naturally by spring.