Getting rid of crown vetch requires attacking the plant on multiple fronts over several years, because this perennial legume spreads both by an extensive root system and by seeds that can remain dormant in the soil for well over a decade. A single round of pulling, mowing, or spraying almost never finishes the job. The plant’s roots store enough energy to regrow from fragments left behind, and its seed bank keeps producing new seedlings long after the parent colony looks dead. The good news is that persistent, well-timed effort does work, and understanding why crown vetch is so stubborn tells you exactly where to focus that effort.
Why Crown Vetch Is So Difficult to Eradicate
Crown vetch (Securigera varia, formerly Coronilla varia) was widely planted across the United States from the 1950s onward for erosion control along highways and slopes. It does that job extremely well, which is precisely the problem when you want it gone. The plant forms dense mats of intertwined stems and sends out long, creeping rhizomes that can extend several feet from the parent crown. Those rhizomes root at nodes along the way, so what looks like a patch of separate plants is often one interconnected colony.
Research on how crown vetch persists has shown that even small fragments of the plant are capable of vegetative regeneration, meaning a chunk of root or stem left in the ground after weeding can sprout into a new colony.1The American Midland Naturalist. Modes of Crown Vetch Invasion and Persistence This trait makes half-hearted removal efforts counterproductive. Ripping out the above-ground growth and leaving broken roots behind can actually scatter viable fragments across a wider area, especially if you’re using a rototiller or pulling carelessly.
Digging and Hand-Pulling
For small patches of crown vetch, hand removal is the most targeted approach, but it demands thoroughness. You need to dig deep enough and wide enough to extract the entire root mass, including rhizomes that extend laterally beneath the surface. A garden fork works better than a spade for this because it loosens soil around roots without slicing through them. Slicing a rhizome into pieces and leaving those pieces in moist soil is essentially planting new crown vetch starts.
Work slowly and trace each runner outward from the central crown. In loose, sandy soils this is tedious but feasible. In heavy clay or rocky ground, it becomes genuinely exhausting for anything larger than a few square feet. After you pull a patch, shake excess soil off the root mass but bag everything and remove it from the site. Composting crown vetch roots is risky unless your pile reaches high temperatures consistently, since fragments can survive and regrow.
Even with careful digging, expect regrowth. Plan to revisit the cleared area every few weeks during the growing season to pull any new sprouts while they’re small and before they’ve had a chance to rebuild their root reserves. This follow-up matters more than the initial removal.
Why Mowing Alone Rarely Works
A common first instinct is to mow crown vetch down repeatedly and try to starve the roots. The logic sounds right: keep cutting the leaves off, and eventually the roots run out of stored energy. But the research paints a less encouraging picture. A study examining seasonal carbohydrate reserves in crown vetch roots found that clipping to about 3.5 inches (9 cm) in late summer or early fall did not significantly affect the seasonal pattern of carbohydrate root reserves and did not lead to winter injury.2Agronomy Journal. Seasonal Variation in Carbohydrate Root Reserves and Crude Protein and Tannin in Crownvetch Forage, Coronilla varia L. Clipping caused only a temporary dip in stored energy before the roots bounced back.
This doesn’t mean mowing is useless. It means mowing alone, at a typical lawn-mowing height, won’t kill an established crown vetch stand. Mowing does prevent the plants from flowering and setting seed, which is valuable for stopping the seed bank from growing. And repeated, very frequent mowing over multiple growing seasons can weaken a stand enough that other methods become more effective. But if mowing is your only tool, you’re in for a long, frustrating campaign with uncertain results.
Smothering With Landscape Fabric or Cardboard
Covering crown vetch with an opaque barrier starves it of light, which eventually kills the above-ground growth and, over time, depletes root energy. Heavy-duty landscape fabric, thick black plastic sheeting, or multiple layers of cardboard weighted down with mulch are the usual options. The barrier needs to extend well beyond the visible edge of the patch because rhizomes will try to escape sideways.
The drawback is time. You generally need to leave the barrier in place for at least one full growing season, and two seasons is safer for dense, well-established stands. Black plastic works fastest because it also generates heat underneath, but it kills everything beneath it and prevents water infiltration, which can damage soil biology. Cardboard layered with wood chip mulch is gentler on the soil but breaks down faster, and determined crown vetch stems can sometimes push through deteriorating cardboard. Whichever material you choose, check the edges regularly and extend the barrier if you see runners emerging outside its perimeter.
Herbicide Options
Chemical control is often the most practical approach for large infestations or for situations where digging is impossible, such as steep slopes. Several herbicide types are effective against crown vetch, each with trade-offs.
- Glyphosate: A broad-spectrum herbicide that kills most plants it contacts. Apply it to actively growing crown vetch, ideally in late spring through early fall when the plant is photosynthesizing and will translocate the chemical into its roots. The downside is that glyphosate kills everything, so any desirable plants nearby need to be shielded or the application must be precise, using a wick applicator or careful spot-spraying rather than broadcast spraying.
- Triclopyr: A selective broadleaf herbicide that kills dicots like crown vetch while leaving grasses largely unharmed. This is useful if your crown vetch is growing in a lawn or a grass-dominated meadow. It’s available in both amine and ester formulations; the ester form penetrates waxy leaf surfaces better but is more volatile in warm weather.
- Clopyralid and aminopyralid: These are in the pyridine carboxylic acid family and target legumes and composites specifically while being less harmful to grasses and many other broadleaf plants. Research on these herbicides found that native forbs seeded into treated plots did not differ in establishment from untreated plots when seeding occurred at least four months after application, suggesting they break down in the soil on a reasonable timeline for replanting.3Invasive Plant Science and Management. Native Forb Establishment following Application of Aminopyralid or Clopyralid
Regardless of the herbicide, one application is rarely enough. Crown vetch roots store substantial energy reserves, and some portion of the colony may not be actively growing when you spray. A common protocol is to spray in late spring or early summer, let the regrowth come up, and spray again in early fall. Some land managers follow this with a third application the next spring. The seed bank means you’ll also need to watch for new seedlings in subsequent years.
Timing matters for translocation. You want the plant to be actively pulling resources down into its roots, which happens most strongly in late summer and fall as it prepares for winter. Spraying during this period tends to move more herbicide into the root system than spraying in spring, when energy flow is moving upward into new growth.
The Seed Bank Problem
Even after you kill every living crown vetch plant on a site, you are not done. Crown vetch produces abundant seed, and a weed management guide cited in a USDA review reports that those seeds may remain viable in the soil for 15 years or more.4Fire Effects Information System. Securigera varia, crownvetch – Section: Seed Banking Anywhere from 20% to 80% of crown vetch seed is “hard seed” with a water-impermeable coat that prevents immediate germination. These hard seeds sit in the soil waiting for something to break their coat, whether that’s physical disturbance, fire, or just years of freeze-thaw cycles gradually weakening the shell.
This means your management plan needs to extend well beyond the initial kill. For at least several years after clearing a crown vetch infestation, you should monitor the site during the growing season and remove or spot-treat any new seedlings before they establish a root system. Seedlings are far easier to kill than mature plants because they haven’t yet built up significant root reserves. Pulling a first-year seedling is trivial compared to digging out a five-year-old colony.
Preventing seed production in the years before you begin eradication helps too. If you know you’re going to tackle a crown vetch patch next year, mowing it before it sets seed this year reduces the additions to the seed bank. Crown vetch typically flowers from late spring through midsummer, so mowing before the seed pods mature is the window to aim for.
Combining Methods for Best Results
The most effective eradication programs combine several approaches rather than relying on any single one. A common sequence for a large infestation goes roughly like this: mow the stand in late spring to prevent seed set and reduce above-ground biomass, let it regrow to about 6 to 8 inches, apply a systemic herbicide during active growth in summer or early fall, then follow up the next spring with either a second herbicide application or hand-pulling of survivors. After the crown vetch appears dead, establish competitive vegetation as quickly as you can to occupy the space before seedlings from the seed bank emerge.
For people who want to avoid herbicides entirely, the combination of thorough digging followed by smothering with landscape fabric, followed by several years of monitoring and pulling seedlings, can work for small to moderate areas. This approach is more labor-intensive, and it takes longer, but it avoids introducing chemicals to the site. The key variable is patience. Crown vetch doesn’t give up easily, and skipping a year of follow-up monitoring can undo previous years of work.
Replanting After Removal
Once crown vetch is knocked back, what you plant in its place matters more than most people realize. Bare ground is an invitation for crown vetch seedlings from the seed bank, as well as other weeds, to fill the vacuum. Establishing dense, competitive vegetation is part of the eradication strategy, not just a landscaping afterthought.
Native warm-season grasses and aggressive perennial forbs are common choices for restoration plantings because they can eventually shade out crown vetch seedlings and compete for root space. However, research on sand prairie restoration found that simply adding native seed had little effect on outcomes regardless of whether herbicide had been applied, suggesting that site preparation and seedbed conditions matter as much as seed selection.5Restoration Ecology. Impacts of management and antecedent site condition on restoration outcomes in a sand prairie In other words, throwing seed onto a poorly prepared site and hoping for the best doesn’t usually work. The site needs adequate soil contact for the seeds, appropriate timing (dormant seeding in fall or early spring is common for native species in cooler climates), and ongoing management of competing weeds during the first few years of establishment.
If you treated the site with clopyralid or aminopyralid, waiting at least four months before seeding native forbs appears to be sufficient for those species to establish without herbicide injury, based on field trials in the upper Midwest.3Invasive Plant Science and Management. Native Forb Establishment following Application of Aminopyralid or Clopyralid Glyphosate has no soil residual activity and is generally safe for replanting within a few weeks of application, though you’ll want to wait until the dead vegetation is cleared or broken down enough to allow seed-to-soil contact.
Dealing With Crown Vetch on Slopes and Road Banks
Crown vetch was planted on slopes specifically because it holds soil in place. Removing it from a steep bank creates an erosion risk that you need to plan for before you start. Killing the crown vetch and leaving bare soil on a hillside invites washouts, especially during heavy rain. The roots will decompose within a year or two of the plant dying, and with them goes the soil-holding structure.
The standard approach is to phase the removal: treat one section of the slope at a time, establishing replacement vegetation on the cleared section before moving on to the next. Erosion blankets, coconut coir mats, or straw wattles can protect bare soil temporarily while new plantings get established. On very steep sites, you may need to accept that full removal happens over three or more years to avoid catastrophic erosion between phases.
Some land managers seed aggressive native grasses like switchgrass or big bluestem into slopes because these species develop deep root systems quickly and can hold soil almost as effectively as crown vetch. In the meantime, a temporary cover crop of annual rye or oats can stabilize the surface during the transition period.
Toxicity and Livestock Considerations
If you’re removing crown vetch from a pasture or from land where animals graze, there’s an additional concern worth knowing about. Crown vetch contains β-nitropropionic acid (BNPA), a compound that is toxic to nonruminant animals. Feeding trials demonstrated that diets containing 0.15% or more BNPA caused reduced feed intake, weight loss, loss of coordination, and death in severe cases among young pigs, chicks, and voles.6Journal of Animal Science. Relationship between β-Nitropropionic Acid Content of Crownvetch and Toxicity in Nonruminant Animals The researchers concluded that crown vetch forage should not be used in nonruminant diets unless the BNPA concentration is extremely low.
Ruminants like cattle and sheep handle crown vetch much better because their digestive systems can break down BNPA more effectively. In fact, cattle and sheep have been used as a management tool to graze crown vetch in some settings, though grazing alone is unlikely to eradicate the plant because the animals don’t consume the roots. Horses, chickens, pigs, and rabbits are the animals most at risk. If you have these animals and crown vetch is growing in or near their pasture, removal becomes a safety issue, not just an aesthetic one. Keep livestock fenced away from the treatment area during herbicide application as well, following the label’s grazing interval for whatever product you use.
Common Mistakes That Let Crown Vetch Come Back
Most failed crown vetch removal attempts share a few patterns. The first is stopping too soon. After a good herbicide application or a season under landscape fabric, the site looks clean and people move on. Then seedlings from the seed bank emerge the next spring, and within two growing seasons the patch is back to its original size. Committing to at least three years of follow-up monitoring is the single most important thing you can do.
The second common mistake is disturbing the soil unnecessarily. Tilling or rototilling a crown vetch patch chops the rhizomes into dozens of fragments, each of which can regenerate into a new plant.1The American Midland Naturalist. Modes of Crown Vetch Invasion and Persistence Tilling also brings buried seeds closer to the surface where conditions for germination improve. Unless you’re following tilling immediately with herbicide application as part of a deliberate stale-seedbed technique, avoid mechanical soil disturbance in areas infested with crown vetch.
The third pattern is leaving cleared ground bare. Crown vetch is an aggressive colonizer of open, sunny ground with low competition. Every square foot you clear and leave unplanted is a square foot where a crown vetch seedling has an easy path back. Getting competitive vegetation established quickly after removal closes that window.
When Professional Help Makes Sense
A backyard patch of crown vetch encroaching from a neighbor’s yard is a reasonable do-it-yourself project. A half-acre slope covered in a decades-old stand is a different animal. Professional land managers or invasive species contractors have access to equipment like boom sprayers and backpack applicators calibrated for precise herbicide rates, and they can work on steep or difficult terrain more safely. They also bring experience with timing and herbicide selection that can shorten the overall eradication timeline.
Many county conservation districts and cooperative extension offices offer guidance on managing crown vetch, sometimes including cost-share programs for landowners dealing with invasive species on conservation land. If your crown vetch problem is in a natural area, a restored prairie, or on land enrolled in a conservation program, check with your local extension office before buying herbicide. They may have site-specific recommendations, and in some cases they’ll help with the work.