Let’s start with non-care: Most lawn grasses are cool-season species that originated in Europe, where the climate is much cooler than ours (or at any rate, it was much cooler until very recently). These grasses can stay green and continue to grow through our hot summers only with continual watering. Without watering, they go dormant, but they green up in early fall, as soon as we get normal seasonal rainfall and the weather turns cool. I’ve been noticing in the past year or so that more and more homeowners are taking advantage of this natural cycle. As someone put it at a talk I gave recently, a brown lawn is a badge of pride this summer! It means you’re not using precious fresh water unnecessarily. It also means that you won’t have to mow until it rains. My husband really likes that!
Early fall, around Labor Day, is the time recommended to feed and renew a lawn. If you feel you must feed your lawn, the best method is to apply a slow-release organic fertilizer around this time of year. The lawn will use those nutrients for fall growth. I’d hold off for a while this year, however. If you lawn is dormant, it can’t possibly use those nutrients, so they’ll just sit there, or, if you water, them in, they’ll flush out into the groundwater (where most lawn fertilizer eventually winds up anyway). If you must feed, wait until the lawn is in active growth. You’ll know when that happens because it will be nice and green again.
As for lawn renewal, wait until the weather turns cooler. Lawn grasses are adapted to cool weather, and seed must stay moist to germinate. If you reseed while the weather is hot, you’ll have to water five or six times a day. If you wait until the weather turns cooler, a brief sprinkle morning and evening will take care of it.
Many people routinely do core aeration in fall. This technique of punching little holes all over the lawn is recommended only for severely worn or compacted lawns, not for most normal healthy lawns. But if you have a place where grass just won’t grow, despite repeated seedings and feedings and treatments, core aeration probably won’t do much good: it’s probably a place where grass really won’t grow because it’s too wet or to dry or too shady. Try planting something else that’s better adapted to the area instead.