Seeding can be done at any time of the growing season, although early fall is the best time. August 15th through September is ideal because weather is usually favorable for seed germination plus competing weeds are declining. The next best time for seeding is Spring. Though, the downside to spring seeding is aggressive competition from germinating weeds. Also with spring seeding, you must avoid applying any Crabgrass pre-emergence since it would prevent the desirable grass seed from germinating as well.