Usually planted in the early fall, cool-season grass seeds prefer daytime temperatures ranging from 60 to 75 F. With this temperature range, the soil itself is usually between 50 and 65 F -- the right environment for germination.f your seeds remain at their ideal temperature range and are planted no more than 1/4 inch deep, you should see germination after three weeks. It is critical to keep the top 1/2 inch of soil moist with a misty spray so the seeds continue to absorb moisture as the seedling grows larger.