Yes, it grows back, but the thin patches almost never close on their own. Lawn repair after crabgrass starts with seed. University of Maryland Extension says to seed the open ground and keep the stand dense enough to crowd new weeds out. That beats waiting on the grass around the hole to creep in. Live turf does spread sideways, so the smallest scars heal without help. Anything wider stays open, and every week of bare soil is another week for weed seed to land.
By the following June that reseeded strip was the thickest grass in the yard, and I could not find the seam where the old turf ended. That was the sixth season on my own tall fescue lawn in central Kentucky. I pulled the dead mats out the September before and put seed straight on the scar. Crabgrass had taken the strip because the grass there was thin and open, and open turf warms the soil and leaves a weed seedling with almost nothing to fight. Michigan State University Extension puts a dense stand first as the best defense against weed invasion.
The hard part is timing. A preemergent stops seed while it germinates, and it cannot tell crabgrass seed from the fescue or bluegrass you just spread. Preemergent and grass seed work against each other in the same few inches of soil. Purdue says it flat out, and the rule is do not put a preemergence herbicide on a recently seeded lawn. Ignore that and you buy seed twice, once in spring and again in fall when the patch is still bare dirt.
Two chemicals break that rule. Wisconsin Horticulture names the pair that does it. They are mesotrione and topramezone, sold as Tenacity and Pylex, and both allow short-term preemergence control of about one month while you seed in spring. One month is a head start, not a season of cover. Crabgrass dies on its own after the first frost in fall, and the seed it dropped all summer sits in the soil and waits for you.
When you overseed after crabgrass has browned out, timing beats product choice. Sow in the window your local extension office lists for your grass type, because a cool-season lawn and a warm-season lawn do not share a calendar. Rake that brown layer off first so the seed reaches soil instead of thatch. Seed lying on a mat of dead crabgrass will not root, and most people blame the seed when the real problem was contact.
Wait until the crabgrass has browned out, then sow at the date your local extension office lists for your grass type.
Leave the preemergent in the shed until the young grass has been cut a few times, unless you picked mesotrione or topramezone.
Set the deck at 3 to 4 inches (7.5 to 10 cm) so the new stand shades the soil and keeps it cool.
Split the year of nitrogen into several small feedings instead of one heavy spring dose.
Feeding rates are regional, so use your own state number and not a figure from a national article. California guidance runs 4 to 6 pounds (1.8 to 2.7 kg) of actual nitrogen per 1,000 square feet (93 sq m) a year, split across 4 to 6 applications. Purdue asks Indiana lawns for 2 to 4 pounds (0.9 to 1.8 kg), laid down in two fall feedings. Both land on the same point, which is steady food that keeps the turf thick.
Seeding bare spots is the cheapest fix on this list and it pays you back the longest. Keep the mower deck high and put seed on any ground you can see through. A thick stand shades out crabgrass better than any bag of chemicals, and it works every month instead of the few weeks a spray covers. I would take dense turf over a perfect spray program every time.
Read the full article: Crabgrass: The Timing That Decides Every Season
