Crown Vetch: Beautiful but Invasive—Use with Extreme Caution

Introduced from Europe in the 1950s for erosion control, crown vetch (Coronilla varia, syn. Securigera varia) quickly escaped cultivation and is now listed as an aggressive invasive across the northeastern U.S. and parts of Canada. While its pink-to-lilac pea-like flowers and dense, low-growing habit make it attractive for tough sites, planting it requires ironclad containment.

Why It Spreads So Aggressively

• Thrives in full sun to light shade
• Tolerates rocky, dry, clay, or shallow soils
• Handles low pH and low fertility
• Hardy in Zones 3–10
• Few insect pests
• Spreads by rhizomes and seeds
• Seeds remain viable in soil for years

These same traits make it useful for steep slopes, roadside banks, and other unmowable areas—but only if it cannot reach cultivated beds, lawns, or natural areas. Deer also browse it heavily.

Establishment: Slow Start, Long Stay

Crown vetch takes 2–5 years to fully establish. It requires specific Rhizobium inoculant (usually supplied with seed) for nitrogen fixation, and will not grow on unlimed soil. Prepare a rough, uneven seedbed—leave rocks and clods for stability. Mulch (straw, wood chips) helps seedlings. Best planting windows: mid-Feb to late March, or mid-Aug to mid-Sept. Avoid summer heat/drought and late fall (winterkill risk).

Varieties

• 'Emerald' – vigorous, taller; suited to Midwest
• 'Chemung' – vigorous, taller; prefers low-fertility Northeast sites
• 'Penngift' – less vigorous

Seed and plants are pricey (~$17/¼ lb seed; $50/30 plants, 2009 prices).

Control: If It's Where You Don't Want It

Small areas: Hand-pull mature plants. Or mow at flowering stage for 2–3 consecutive years before seeds mature.

Herbicides (active growth only):

• Triclopyr (broadleaf-selective; spares grass)
• Glyphosate (non-selective)
• Metsulfuron

Always read labels; follow safety practices.

Large areas (pastures, prairies): Consult your local extension agent.

Toxicity Notes

Reports vary: some sources cite danger to horses; cattle seem unaffected. No human toxicity documented. Horses may avoid it voluntarily.

Bottom line: Crown vetch is a powerful tool for impossible slopes—but treat it like a confined animal. Plant only where rhizomes and seeds are physically blocked from escape. Otherwise, choose a non-invasive groundcover.

Sources: Univ. Missouri Extension, Univ. Kentucky Agronomy, Southeast Exotic Pest Plant Council, Ohio State Weed Guide. First two photos: Wikimedia Commons (GNU). Third: Ohio State Weed Lab Archives.