Ornamental · Fabaceae
Hairy Vetch
Vicia villosa
Sown in fall, this nitrogen-fixing cover crop builds soil nitrogen through winter and into spring.
Full sun
Every 7–14 days
180–240 days
USDA 4–8
Overview
Hairy vetch is a cool-season legume cultivated chiefly as a cover crop and green manure rather than an ornamental. Its trailing, vine-like habit produces a mat of fine, feathery leaves and it climbs available support with tendrils, which is why it is so often drilled with cereal rye. The violet-purple to blue-purple flowers appear in spring, marking the point at which the stand is typically terminated.
The plant's agronomic value lies below ground. As a legume it forms a symbiosis with Rhizobium bacteria that fix atmospheric nitrogen into root nodules, and that nitrogen is released to the soil as the terminated residue decomposes. A well-nodulated stand can meet much of the nitrogen demand of a following corn crop, which is why it substitutes for part of the fertilizer program.
Two limitations temper its usefulness. Because it is hard-seeded it reseeds readily and can persist as a weedy volunteer if allowed to set seed. And in contrast to clover, heavy grazing can poison cattle and horses, so it belongs in the rotation as a soil-building crop first and a forage a distant second.
Care
The short version: full sun, well-drained ground, and seed inoculated with the right Rhizobium. Sow in fall so it fixes nitrogen through winter, then terminate at flowering before it sets seed.
Light
It performs best in full sun and tolerates partial sun with little penalty. Greater light supports denser canopy and higher nitrogen fixation, so an open site is preferable where available.
Water
Once established the plant tolerates dry, well-drained soil and draws on fall, winter and spring moisture, so supplemental irrigation is seldom warranted outdoors. Waterlogging is the exception it cannot tolerate, because saturated soil predisposes crown and root rot.
Soil
It grows on well-drained sandy to loam soils and tolerates low fertility and some acidity, with a preferred pH of 6.0 to 7.5. Its nitrogen requirement is minimal, but adequate phosphorus, potassium and sulfur are needed for full vigor and nodulation.
Temperature
This is a hardy cool-season species, cold-tolerant across roughly -20°F to 75°F (-29°C to 24°C). That hardiness underpins its function as an overwintering cover crop through zones 4 to 8.
Humidity
Ambient outdoor humidity is sufficient, so no target applies. Air movement is the greater concern, because a dense, humid canopy is what allows crown rots to establish.
Feeding
As a legume the plant fixes its own nitrogen through Rhizobium nodules, so nitrogen fertilizer is unnecessary and counterproductive. Ensure effective inoculation and supply adequate phosphorus, potassium and sulfur instead.
Pruning
No pruning is required in ornamental use. The functional equivalent for a cover crop is termination by mowing, rolling or crimping at flowering, or tilling in, done before mature seed forms so the nitrogen is released and reseeding is avoided.
Repotting
none
Size & spacing
The stand attains 3 to 12 feet (90 cm to 3.7 m) of trailing growth, with individual plants spreading about 2 to 6 feet (60 to 180 cm) as they climb over neighbors. Sown at cover-crop density it interlaces into a continuous mat rather than persisting as discrete plants.
When to plant
Hairy vetch follows a fall-to-spring cycle. Sow about 30 to 45 days before the killing frost so the seedlings establish before dormancy, allow the stand to overwinter, and terminate at flowering in spring to release the fixed nitrogen and prevent hard-seed reseeding.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Not started indoors; direct sown outdoors
- Plant: Late summer to fall, about 30 to 45 days before killing frost, to overwinter; often mixed with cereal rye for support
- Harvest: Violet-purple to blue-purple flowers in spring; terminate at bloom for green manure
Hardiness
USDA hardiness zones: 4–8
Temperature: down to -34°C
Troubleshooting
Nearly all hairy vetch problems reduce to three mechanisms: hard-seed reseeding, failed establishment, and moisture-driven rots or spring aphids. The entries below tie each symptom to its cause so you can correct the underlying condition rather than the symptom.
Volunteer vetch recurring in subsequent crops
The mechanism here is hard-seed reseeding, the chief liability of carrying a stand to maturity. Roughly 10% to 20% of the seed sets a hard, water-impermeable coat, so it can persist dormant in the soil profile for a season or longer, germinate in a later grain or vegetable crop, and encroach along field margins. Terminating at flowering, before any seed matures, removes the source, and cultivating or spot-treating escaped seedlings before they flower keeps the seedbank from renewing.
Fix:
- Terminate the stand at flowering, before mature seed forms, by mowing, rolling/crimping or tilling
- Cultivate or spot-treat volunteer seedlings before they flower
Weak chlorotic stand fixing little nitrogen
In most cases the root cause is failed inoculation. Absent the correct Rhizobium on the seed, the symbiosis does not form, few nitrogen-fixing nodules develop, and the foliage stays chlorotic and weak because the plant cannot access atmospheric nitrogen. Late sowing, poor seed-to-soil contact, waterlogging, or shortages of phosphorus, potassium and sulfur compound the problem. Excavate several roots to look for pink, active nodules, then reinoculate with fresh vetch or pea Rhizobium, drill or firm the seed 30 to 45 days before killing frost, and correct the drainage.
Fix:
- Inoculate seed with the correct vetch/pea Rhizobium before sowing
- Drill or firm seed for good soil contact and sow 30 to 45 days before killing frost
- Choose well-drained sites and correct P, K and sulfur deficiencies
Crown rot and spring aphids on the stand
Poorly drained soil favors root and crown rots such as Sclerotinia, whose soilborne fungi advance through saturated tissue and leave soft, discolored crowns and white mycelial growth at the base. Aphids are the second spring pressure, colonizing succulent new shoots and leaf undersides. Siting on well-drained ground denies the fungi the moisture they need, rotation away from legumes lowers inoculum where rots build, and the lady beetles that vetch attracts suppress aphid populations biologically.
Fix:
- Improve drainage and avoid waterlogged sites
- Rotate away from legumes if soilborne rots build up
- Encourage lady beetles and other beneficials, which vetch attracts, to manage aphids
Toxicity
The growing plant is low risk to cats, dogs and people, and the foliage is acceptable to rabbits and birds in moderation. The seeds concentrate mild toxins and should be kept out of reach. The material warning concerns grazing animals, because heavy hairy vetch can cause fatal toxicosis and bloat in cattle and horses, so pure or dense stands must never be grazed.
Toxic to
Horses · Livestock
Safe for
People · Cats · Dogs · Rabbits · Birds
Horses Caution
Sustained grazing of dense vetch is the material hazard. Horses can develop hairy vetch toxicosis, presenting with pyrexia, dermatologic lesions, alopecia and weight loss, while a rich legume stand can additionally precipitate bloat.
Livestock Caution
Cattle carry the same exposure risk as horses. A ration dominated by hairy vetch can induce fatal granulomatous toxicosis, with fever, dermatitis, alopecia and weight loss, compounded by conventional legume bloat, so pure or dense stands should never be grazed.
Cats Safe
The vegetative foliage presents low risk to a cat. Ingestion of a large quantity of plant, or more commonly the seeds, may provoke a transient gastrointestinal upset, but nothing of consequence.
Dogs Safe
The picture parallels cats. Chewed foliage generally passes without effect, whereas a dog that ingests a bolus of seeds may show self-limiting vomiting or loose stool.
Rabbits Safe
Moderate quantities of the leafy growth are acceptable within a mixed forage. Exclude the seeds, which concentrate the plant's mild toxins.
Birds Safe
Foraging birds tolerate the foliage without incident. Because the seeds hold mild toxins, they are not an intended feed.
People Safe
This is an agronomic crop rather than a food plant. Handling carries no meaningful hazard, though the raw seeds and sprouts contain L-canavanine and are not edible.
The growing cover-crop foliage is low risk for pets; keep cats and dogs from gorging on plants and especially from eating the seeds. The greater hazard is to grazing livestock: do not let cattle or horses graze pure or heavy hairy vetch stands, which can trigger hairy vetch toxicosis and bloat.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
Only a small number of named selections reach the commercial seed trade, most of them bred for improved winter survival and earlier spring maturity.
'Purple Bounty'
A cold-hardy release selected for northern winter survival and early flowering, which advances the spring termination window.
'Purple Prosperity'
A companion selection to 'Purple Bounty' with dependable overwintering and early maturity that supports the same earlier spring termination.
Common vetch (Vicia sativa)
A related cover crop bearing larger seed and lower cold tolerance than hairy vetch, whose seeds carry the same vetch toxicity concerns.
Companions
Hairy vetch pairs best with a sturdy grain it can climb and a heavy feeder that wants the nitrogen it leaves behind, and worst with the winter grains it can contaminate by reseeding.
Plant near
Cereal rye: Rye provides a sturdy structure for the climbing vetch tendrils to scramble up, improves weed suppression and residue, and balances the nitrogen contribution
Corn: Hairy vetch terminated in spring supplies a large flush of fixed nitrogen that can partially replace fertilizer for a following corn crop
Keep apart
Winter wheat or other winter grains: Hard-seeded vetch readily reseeds and becomes a contaminating volunteer weed in winter grain crops
How to propagate
Hairy vetch is propagated in one way, by direct seeding into the soil, with correct inoculation being the decisive factor in establishment.
SeedEasy
Late summer to fall, about 30 to 45 days before killing frost, for overwintering · Establishes in fall, grows slowly over winter, then accelerates in spring
Propagation is by direct seeding into the soil in late summer to fall, about 30 to 45 days before the killing frost, which gives the seedlings time to establish ahead of winter. Inoculate the seed with the proper Rhizobium beforehand to ensure nodulation, then drill it at roughly 15 to 20 lb per acre or broadcast 25 to 30 lb per acre, commonly in mixture with cereal rye for support. The stand establishes in autumn, remains largely dormant over winter, and resumes vigorous growth in spring as soil temperatures rise.
Myths
Legume cover crops such as vetch provide harmless grazing on par with clover.
Hairy vetch is a sound nitrogen-fixing cover crop, yet it does not equal clover as forage. Its seeds contain L-canavanine and, in some vetch seed, cyanogenic compounds, and heavy grazing can induce hairy vetch toxicosis, a systemic granulomatous disease, together with bloat in cattle and horses. Regard it as a soil crop, not as safe pasture.