The best time to seed cool season grasses, such as Kentucky bluegrass and tall fescue, is between Aug. 15 and Sept. 15, so it’s time to start your site preparation.
Getting your seeding done as early as possible is really important, because each week of delay in seeding translates into 2 to 4 additional weeks required for the grass to mature in fall. It is critical to seed tall fescue no later than mid-September. Tall fescue seedlings take a longer time to develop cold hardiness, so get your seeding done early.
Fall is, in fact, the best time of year for seeding lawns due to a combination of factors. First, there’s less weed pressure than in spring, and late summer weather is less problematic during the soil preparation phase. Plus, the extended period of cool weather, usually with good rainfall, that occurs from September through late November is ideal for growth of cool season turfgrasses.
Total renovation: If you need to renovate the entire lawn, start by killing the remaining grass and weeds with glyphosate (RoundUp), then wait for 10 to 14 days for the herbicide to take effect. Next, mow the dead vegetation as short as your mower will allow and move on to soil preparation.
Overseeding: If you just need to fill in thinned areas, and still have more than 50% good turf then overseeding is the answer. Skip the RoundUp, but mow the existing grass fairly short, 2.5 to 3 inches tall, to make the next step — soil preparation — easier.