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A bottle of ordinary broadleaf weed killer sprayed twice, over two weekends, on a patch of what looks like fast-growing grass barely slows it down, and the patch keeps outgrowing the rest of the lawn by inches within days of mowing. That is the classic sign that it isn’t grass at all — it is yellow nutsedge, which is botanically a sedge, not a grass, and that distinction is exactly why a general lawn herbicide does nothing.
Most lawn weed killers are formulated for broadleaf weeds or grassy weeds specifically, and nutsedge is neither — it needs its own category of herbicide entirely, which is the single most important thing to know before you spend money on the wrong product.
Identification
The fastest tell: nutsedge grows visibly faster than the surrounding turf and looks noticeably taller within just a few days of mowing, even though everything was cut to the same height. Look closely at the stem cross-section — true grasses have round or flat stems, while sedges have a distinctly triangular stem, which is where the old gardener’s rule “sedges have edges” comes from. The leaves are also glossier and more upright than most turf grasses, with a slightly waxy sheen. Yellow nutsedge (the more common lawn species) has light green to yellowish foliage and yellowish-brown seed heads by midsummer; purple nutsedge is darker green with reddish-purple seed heads and tends to show up more in warm, consistently moist soil.
Why it shows up
Nutsedge thrives specifically in soil that stays wet longer than it should — poor drainage, low spots, over-irrigation, or a leaking sprinkler head are the usual culprits. It spreads primarily through underground tubers (the “nut” in the name) rather than surface seed, which is a big part of why it’s so persistent: a single plant can build an underground network of tubers that keeps producing new shoots even after you’ve removed everything visible above the soil.
Control, step by step
1. Use a sedge-specific herbicide, not a general weed killer. Products built around halosulfuron are the standard here — they’re labeled specifically for nutsedge and safe for most common turf types when used as directed, unlike broadleaf or grassy-weed formulas that largely pass right over sedges. Expect to see visible yellowing within a week or two, but plan on a second application a few weeks later: University of Arizona extension guidance notes that most labels for this class of herbicide recommend a follow-up about 4 to 6 weeks after the first (Strategy for Nutsedge Control in Turf), and a single treatment rarely kills the full underground tuber network in one pass. Check your product label for the exact interval.
2. Don’t pull it by hand unless you’re prepared to keep doing it. Hand-pulling breaks the top growth but almost always leaves tubers behind in the soil, and disturbing the soil can actually distribute small tubers to new spots. If you’re going to try mechanical removal at all, dig several inches down and around the base to get the full tuber cluster, not just a quick pull.
3. Fix the moisture problem, or the herbicide is just playing defense. If a spot has nutsedge, it’s telling you something about drainage or irrigation in that exact location. Redirecting a sprinkler head, improving grading, or aerating compacted soil in the affected area addresses the actual condition nutsedge needs to keep coming back, rather than just knocking back this season’s growth.
4. Be patient about timing. Nutsedge is a warm-season grower that dies back with cold weather and re-sprouts from tubers the following year, so treatment works best from late spring through summer, while it’s actively growing, rather than in fall when it’s already declining on its own.
Product options
This halosulfuron-based nutsedge killer is the category to reach for specifically because it’s formulated for sedges rather than general lawn weeds — check the label for your specific turf type before applying, since a few grass species have restrictions.
A few things people ask
Why didn’t my regular weed and feed touch it? Because nutsedge isn’t a grass or a broadleaf weed — it’s a completely different plant family, and most all-purpose lawn herbicides simply aren’t formulated to affect it. This is the single most common reason people feel like they’ve “tried everything” on a patch that turns out to just need the right specific product.
How long until it’s actually gone for good? Because of the underground tuber network, full control realistically takes more than one growing season in an established patch — expect noticeable improvement within weeks but plan on watching the same spot again next year, especially if the underlying moisture issue hasn’t been fully corrected.
Is nutsedge a sign my lawn is unhealthy overall? Not necessarily the whole lawn — it’s usually a very localized signal about that specific spot’s drainage rather than a reflection of your lawn care in general. A single low corner or an old sprinkler head with a slow leak is a far more common cause than anything happening lawn-wide.
If the fast-growing patch in your yard doesn’t match the sedge signs above, it may just be crabgrass instead, which needs its own separate treatment approach.
The identification step matters more here than with almost any other lawn weed, because grabbing the wrong bottle wastes money and a growing season without touching the actual problem. If a patch is outgrowing your mowing schedule and a regular weed killer isn’t making a dent, checking for that triangular stem is worth doing before buying anything else. Next reads: Dandelion Identification and Control: Why They Keep Coming Back, Clover in Your Lawn: Kill It or Keep It? Here’s How to Decide and Brown Patch Lawn Disease: Identification and Treatment.