Late August and September are good times to rake up and reseed bare patches in your lawn. (If you live downstate or on Long Island, this period extends to mid-October.) If your lawn is more than 50 percent weeds, consider a total renovation.
Wait until Labor Day or later until plants recover from summer stress before fertilizing. At least 50 to 75 percent of home lawn fertilizer applications should be made between Labor Day and Thanksgiving. Around Labor Day is a good time to apply 1 lb. N/1,000 square feet to encourage strong roots for overwintering. A single fertilization later in fall is all many home lawns need.
Late July through September is a good time to scout for grubs to see if there are enough to justify treatment. Treating for grubs in spring as they near maturity is often not effective. Pesticide applications, if needed, should be while the grubs are still young and vulnerable. Sometime in August is usually best. Shaded Kentucky bluegrass lawns established more than 15 years ago are most susceptible to grub damage.
Continue to follow the “One-Third Rule,” never removing more than one-third of the plant. (If you set your mower to mow at 3 inches, mow before the grass reaches 4.5 inches tall.) As temperatures cool, grass growth should speed up (if moisture is adequate) and you’ll need to mow more often than you did in summer.
Healthy growing lawn needs about 1 inch of water per week. Use a rain gauge or coffee can to measure how much you receive. If it’s less than an inch, you can water to make up the difference.
Post-emergent herbicides are particularly effective on broadleaf weeds in fall. That's because the weeds are storing up nutrients for the winter, and move the herbicides down into the roots along with the nutrients, giving a better kill. If ground ivy (creeping Charley) is a problem, any product with 2,4-D can provide good control when applied immediately after the first frost. Avoid applications when temperature is below 50 F or before an expected rainfall.