The answer to 'when to grass' is the best time to plant new grass or overseed an existing lawn is in the fall, typically between September and November. This is because the cooler temperatures and increased rainfall in the fall provide ideal conditions for grass seed germination and establishment.
Fall is the prime growing season for cool-season grasses like fescue, bluegrass, and ryegrass, which are common in many residential landscapes. The soil is still warm enough to support rapid root growth, while the air temperatures are moderate and the grass has less competition from weeds. This gives the new grass the best chance to take hold and become well-established before the winter dormancy period.