Why September is the best month to overseed

The cool-season grasses that make up most Lancaster County lawns — tall fescue, Kentucky bluegrass and perennial ryegrass — grow fastest when the soil is still warm and the air has cooled off. Early fall is the one stretch of the year that offers both.

Weeds are slowing down by then too, so new seedlings face less competition than they would in spring, and they have two full growing seasons — fall and the following spring — to root in before summer heat arrives.

Getting it right

• Core aerate first, so seed lands in the holes rather than on top of thatch.
• Keep the seedbed moist with short, frequent watering until the new grass is up.
• Hold off on weed control that would also stop the seed from germinating.