“It’s possible that your lawn needs other measures," says former Test Editor Roy Berendsohn. "For example, a better fertilizer regimen, core aeration ... of lawn dethatchers: Manual dethatchers, a ...

By removing small plugs of soil ... usually the best results come from a gas-powered, push-behind core aerator. Most yards benefit from lawn aeration once a year, but some need it more often ...

Core aeration ... roots to push deeper in the soil. Machines can be rented from many nurseries, hardware stores or rental agencies for a nominal fee. They are slightly larger than a lawn mower.