The best time to aerate a lawn is early in the growing season so the grass has time to heal and grow back. For warm-season grass, this means aerating in the late spring or early summer months. Cool-season grass does best with aeration in the fall.
Environmental factors affect the frequency and timing of lawn aeration. Because of their compact nature, lawns growing in clay soils often need aeration every year. Yards with sandy soil likely only need aeration every other year.
Timing the lawn aeration before fertilization allows the fertilizer to better reach the roots, as the holes creating through aeration allow nutrients to penetrate the soil. Moist but not saturated soil works best when aerating. It is best not to aerate a lawn during a drought or during a period of high temperatures, as it adds stress to the grass.