The best time to aerate a lawn depends on the type of grass:

• For cool-season grasses (common in northern lawns), the best time to aerate is early fall or early spring when the grass is in its peak growing period. Aeration in fall helps nutrients reach the roots with cooler temperatures and moist soil aiding seed germination.
• For warm-season grasses (common in southern lawns), aerate in late spring or very early summer during the active growth phase for quick recovery.

Aerating should be done when the soil is moist but not overly wet to make the process easier and more effective. Lawns on heavy clay soils or with heavy foot traffic may need annual aeration, while lawns on sandy soils with less use may need it every 2 to 3 years. Aeration is best done along with other lawn care practices like fertilization, overseeding, dethatching, and topdressing for optimal lawn health.