Johnson Grass in Your Lawn: How to Identify It and Kill It for Good

Johnson Grass vs Crabgrass, Dallisgrass, and Quackgrass

These four get mixed up in lawns all the time, and each one needs its own fix. Johnson grass and quackgrass run on rhizomes, dallisgrass is a clumping perennial, and crabgrass is a summer annual.

A broad leaf with a white stripe down the middle, on a plant that comes back from thick, fleshy rhizomes, is Johnson grass. Narrow auricles clasping the stem mean quackgrass. A low, sprawling plant that sprouted this spring is crabgrass, and a tough clump with a few seed-head branches lined with hairy spikelets is dallisgrass.

Does Johnson Grass Come Back Every Year?

Yes. Johnson grass is a perennial, per NC State and the USDA PLANTS database, so the same plant regrows from its rhizomes each season. The Washington State Noxious Weed Control Board adds that its seeds stay dormant in the soil for several years, so new plants can keep coming up from seed even after the old clumps die.

What Kills Johnson Grass but Not the Lawn?

On bermuda, zoysia, St. Augustine, and centipede, sulfosulfuron, sold as Certainty Turf Herbicide, kills Johnson grass without killing the lawn. Its EPA label allows residential turf, calls it generally safe on those grasses, and lists Johnsongrass at 1.25 to 2.0 ounces of product per acre. Tall fescue and Kentucky bluegrass lawns get a glyphosate spot spray.

Certainty on a Warm-Season Lawn

Certainty's label converts the per-acre rate for hand-held sprayers, which go on at 2 gallons of spray per 1,000 square feet. One large scoop (the 0.8-gram scoop in the package) in 2.0 gallons of water gives the 1.25-ounce rate. Two large scoops in 2.5 gallons give the 2.0-ounce rate, which the label says to use on established, dense infestations. Add 2 teaspoons (1/3 fluid ounce) of nonionic surfactant per gallon.

Spray Johnson grass while it's actively growing, and hold the mower off for at least 2 days before and 2 days after. The label gives no height for Johnsongrass, so on a warm-season lawn you keep mowing on your normal schedule outside that window. Expect the weed to yellow or brown within 2 to 3 weeks. If you started at 1.25 ounces, a second 1.25-ounce application can go on 4 or more weeks later if needed, with no more than 2 applications a year.

The label also warns of temporary yellowing and delayed green-up in the lawn itself, and says drought-stressed weeds are less susceptible. Heavy rain or irrigation within 2 hours can wash it off the leaves.

Glyphosate on Tall Fescue or Bluegrass

On a cool-season lawn, Illinois Extension's timing applies: it sprays glyphosate from June to August, when the plant is at least 18 inches tall and until it starts to flower, at a 2% solution by volume in water. Mississippi State adds that the plant should be actively growing and free of adverse environmental conditions. In a mowed lawn, I'd mow around the clump for a few weeks so there's enough leaf to take the spray, then reseed or sod the dead spot with your lawn grass.

Work with a hand-pump sprayer on a calm morning, and shield the turf around the clump with a piece of cardboard. The tank mix calculator turns a percentage like 2% into ounces for a one-gallon sprayer. Mississippi State's table lists 32 herbicides and premixes that control Johnson grass across many application sites, sulfosulfuron among them, and it sends you to each label for sites and rates. On bermuda, the guide to bermuda-safe weed control covers what else you can spray without losing the lawn.

Should You Pull Johnson Grass?

Pull seedlings, dig small clumps, and spray established patches. Mississippi State says hand removal is difficult because Johnson grass has long rhizomes, though it may be feasible for small patches in a landscape or vegetable garden. Leave a rhizome piece behind and it can sprout.

A seedling with the seed still attached comes out clean if the soil is moist. A clump that has been there a season needs a spade. Get the blade under it, lift the whole root mass, and sift the soil with your fingers for white rhizome pieces. Bag them; don't compost them.

Mowing alone won't finish it either. Illinois Extension says mowing can keep the plant from flowering and spreading seed but won't eradicate it, and Mississippi State agrees that mowing does not generally eradicate Johnson grass. Keep the mower on it to stop the seed while you work on the roots.

Where Johnson Grass Gets Into a Lawn

NC State notes that Johnson grass is uncommon in turf and doesn't grow well under frequent, close mowing. It lives on roadsides, pastures, and disturbed fields. So when a homeowner calls me about it, I don't start in the middle of the yard. I walk the edges: the back fence, the ditch, the corner behind the shed the mower skips, and the low spot somebody filled last spring.

A homeowner trucks in a load of fill to level a wet corner, seeds it, and by midsummer there's a clump of broad, white-striped grass standing above everything around it. Mississippi State says Johnson grass spreads through rhizomes in soil, seed on equipment, and contaminated seed or hay, and that moving contaminated soil spreads it too. Ask where your soil came from before it's dumped in the yard.

How to Keep Johnson Grass From Coming Back

NC State's prevention advice for perennial grass weeds in turf comes down to three habits. Mow at the recommended height for your grass and remove clippings when grassy weeds have seed heads. Fertilize with the right amount of nitrogen at the right time for your grass type. Use a soil test to set nutrients and lime.

Two more habits help. Mississippi State notes that Johnson grass generally doesn't tolerate deep shade, and a thick, well-fed lawn gives it less open ground to take. Walk the edges every few weeks through summer and deal with each new sprout while it's small. The mowing height calculator gives you the height for your grass.

Put a Name on It Before You Mix Anything

Crabgrass, dallisgrass, and young Johnson grass look alike when they're small. Spraying glyphosate on a patch of crabgrass costs you a lawn patch to kill an annual that a pre-emergent would have stopped. Snap the leaf, the collar, and the seed head with the free photo diagnosis, or run a picture through the weed identifier.

Once you know what you're dealing with, WGIS Premium adds seasonal reminders timed to your ZIP code and grass for the mowing and feeding that keep the edges thick, and you can set your own reminder for the follow-up spray.

Your Johnson Grass Action Plan

1. Confirm the ID: a white midrib, thick rhizomes, and a purplish panicle. Use the comparison table or a free photo diagnosis.
2. Pull seedlings with the seed attached, and dig small clumps with every rhizome piece.
3. Bermuda, zoysia, St. Augustine, or centipede: spray actively growing Johnson grass with Certainty and nonionic surfactant at the label rate, with no mowing for at least 2 days on either side. Test St. Augustine on a small area first.
4. Tall fescue or bluegrass: let the clump reach at least 18 inches between June and August, spot-spray glyphosate before it flowers, then reseed or sod the dead spot.
5. Check back in 4 weeks and re-treat regrowth within the label's limits.
6. Mow the edges, bag clippings when seed heads show, and check where fill soil came from.