Hot, Humid Weather Is Tough on Grass Seedlings
The hot, wet and humid weather conditions experienced across the northern US are likely to lead to disease and death problems in young seedlings. Mature turf is more tolerant. Extreme summer-like conditions are not a good time to plant northern grass seeds, such as bluegrass, ryegrass, and fescues, or to have young seedlings fighting to survive. Northern grasses are best planted during early spring and early fall when soil temperatures are between 50F and 75F. That's when those grasses will have time to mature. Unless you have to seed to stop erosion, hold off on seeding until nighttime air temperatures are consistently less than 65 and daytime temperatures are consistently less than 80 between the middle of August and Late September.