Sedge grass

Roll a stem between your fingers

Sedges are not grasses, and the test takes two seconds. Nutsedge stems are triangular in cross-section, so a stem rolled between finger and thumb has three flat sides and edges you can feel. A grass stem is round or flattened, and rolls smoothly.

That single check settles the most important question in the whole problem, because almost every weedkiller sold for lawns is designed for broadleaf weeds or for grasses, and sedges are neither. Spraying the wrong product is why people report that nothing works.

The supporting signs are easy once you know them. Leaves come off the stem in sets of three, arranged in three ranks rather than the two of a grass. The foliage is yellow-green and noticeably shiny. And it grows faster than the lawn, so the patch is visible three days after mowing as a tuft standing above everything else.

Sedges also prefer moist or wet ground, which is the first clue about why it is there at all.

Weeds that look like grass

The triangular-stem test settles sedge, but sedge is only one of several things in a lawn that pass for grass at a glance. Working out which one you have decides the product, because three of the plants below are not grasses at all and are unaffected by anything sold for grassy weeds.

Two shortcuts save most of the work. Crush a leaf and smell it: onion or garlic means wild onion or wild garlic, and nothing else in the list smells of anything. Roll the stem: three edges means sedge. If it neither smells nor rolls with edges, it is a grass, and the question becomes which one.

That last distinction matters because the treatments do not overlap. Sedge needs a product naming sedge or nutsedge. Wild onion and wild garlic are broadleaf-type targets despite looking like grass. Grassy weeds in a lawn need either a pre-emergent for the annuals or spot treatment for the perennials, since nothing selective removes a perennial grass from a grass lawn.

Grass killer for flower beds

A grassy weed running through a bed is a different problem from one in a lawn, and it is the easier of the two, because in a bed the grass is the only monocot present.

Grass-selective herbicides exist for exactly this. The active ingredients are clethodim, fluazifop-p, sethoxydim and fenoxaprop-ethyl, and they control grasses without touching broadleaf plants. They are systemic, so they move into the roots rather than only burning the top, and their soil residual is short, on the order of two weeks. That combination is what makes them usable over the top of most flowers and shrubs.

• Read the label for your plants. Safe around most ornamentals is not the same as safe around all of them, and the labels differ by product. Test on a small area before treating a whole bed.
• Spring or fall, on cool calm days. Spring treatment catches the weeds before they get large or set seed, and cool still conditions limit drift.
• Shield anything precious. An upturned bucket or box over a plant while you spray around it costs nothing and removes the drift question entirely.
• They will not touch sedge. Sedges are not grasses, so a grass-selective product does nothing to nutsedge in a bed any more than lawn weedkiller does in turf.

For a perennial grass with rhizomes, expect to repeat. A systemic product moves through the plant it contacted, and a rhizome network running under a bed from outside it keeps sending up new growth from tissue that was never treated.

Removing grass from a yard

Turning turf into a bed is the other half of this question, and the method depends on how long you can wait.

• Smothering is the slowest and the least work. Cardboard or thick paper covered with mulch, left in place for a season, kills most turf without digging. It fails against established perennial grasses with deep rhizomes.
• Sod cutting is immediate and physical. It removes the turf and the top inch or two of soil with it, which takes the crowns but not deeper rhizomes.
• Spot treatment with a non-selective herbicide is what Iowa State describes as typically the most effective route against perennial grasses, applied in midsummer, with replanting or reseeding a week later.

Whichever route, deal with the reason the ground was worth converting. A bed made where the grass was thin because the site is wet, shaded or compacted inherits the same problem, and on a wet site it inherits the sedge as well.

Why it keeps coming back

Pulling nutsedge feels productive and usually makes the problem worse.

Yellow and purple nutsedge are perennials that reproduce prolifically by underground tubers, the nutlets that give the plant its name, as well as by seed. A single plant sits on top of a network of them. Pull the top and the tubers respond by sprouting, so one plant becomes several.

That is the whole difficulty in one sentence: you are not fighting the plant you can see, you are fighting a bank of tubers you cannot. Small, young infestations can be dug out if you take the tubers with them. Established patches cannot be weeded away.

Fix the conditions first

Nutsedge favors wet ground, so a patch is often telling you something about the site.

1. Find out why it is wet

   A leaking irrigation head, a downspout discharging onto the lawn, a compacted low spot or genuinely poor drainage. Nutsedge in one recurring patch usually has a cause you can see once you look.

2. Water less often and more deeply

   Frequent shallow watering keeps the surface damp, which suits sedge and does not suit turf roots.

3. Thicken the turf

   Extension guidance on weeds in lawns comes back to the same point: cultural practices that increase the density and vigor of the desirable turf. Correct fertilizing, liming to the soil test and appropriate watering do more over two seasons than any spray.

4. Mow at the top of the range for your grass

   Taller turf shades the soil surface. Sedge seedlings and sprouting tubers need light.

5. Deal with compaction

   Aerating a compacted low area attacks the wetness that the sedge is exploiting.

When a herbicide is warranted

For an established patch, cultural work alone will not clear it, and the product that matters is halosulfuron, effective against both yellow and purple nutsedge. Clemson lists it as the active ingredient in SedgeHammer Plus, Hi-Yield Nutsedge Control, Martin’s Nutgrass Eliminator and Monterey Nutgrass Killer II.

Two details in that guidance decide whether it works. The products require a nonionic surfactant at 2 teaspoons per gallon of water, without which the spray beads off the waxy leaf. And the treatment may need repeating in 6 to 10 weeks for complete control, because the first application does not reach every tuber.

Expecting one spray to finish it is the most common reason people conclude the product failed. Two applications, a couple of months apart, with the surfactant, is the treatment as written.

The label on the container you own is the authority on rates, on which turf species tolerate it and on any restriction where you live. Some warm-season and some cool-season grasses respond differently, and that is decided by the label rather than by an article.

What does not work

Ordinary broadleaf lawn weedkiller does nothing to a sedge. Neither does a grass-specific product. The plant is in a third family and needs a product that names sedge or nutsedge.

Pulling established patches multiplies them, for the reason above. Pre-emergent herbicides aimed at crabgrass do not touch tubers already in the soil, which is how nutsedge appears in a lawn that was treated in spring.

And a patch cleared without changing the wet conditions comes back, because the site still suits it better than it suits the grass.

Frequently asked questions

How do I know it is nutsedge and not grass?

Roll a stem between your fingers. Sedge stems are triangular with three flat sides; grass stems are round or flattened. Leaves also come off in sets of three, the foliage is shiny yellow-green, and it grows faster than the lawn so it stands proud within days of mowing.

Why does it come back after I pull it?

Because it reproduces from underground tubers. Pulling the top leaves the tubers, which sprout in response, so one plant becomes several. Only small young infestations can be dug out, and only if the tubers come with them.

Will normal weedkiller kill it?

No. Sedges are neither broadleaf weeds nor grasses, so products aimed at either do nothing. The product has to name sedge or nutsedge; halosulfuron is the active ingredient effective against both yellow and purple nutsedge.

Why did one spray not clear it?

Because that is not the treatment. Clemson’s guidance is a nonionic surfactant at 2 teaspoons per gallon, and a repeat application in 6 to 10 weeks. Without the surfactant the spray beads off the leaf, and without the repeat the surviving tubers resprout.

Why is it in my lawn at all?

Sedges prefer moist or wet ground, so a recurring patch usually marks a leaking sprinkler, a downspout, a compacted low spot or poor drainage. Clear the patch without fixing that and it returns.