The optimal window for core aeration and overseeding in Southeastern PA is late August through mid-October, when soil temperatures drop below 70°F but stay above 50°F. This aligns with cool-season grass germination windows for tall fescue, Kentucky bluegrass, and perennial ryegrass across Montgomery, Bucks, Chester, Delaware, Lehigh, Berks, and Philadelphia Counties. New seed needs 6 to 8 weeks to establish before the first hard frost, typically November in most of the service area. Avoid heavy foot traffic and mowing below 3 inches on newly seeded areas for the first 4 weeks.