Ornamental · Fabaceae
Hairy Vetch
Vicia villosa
Sow it in fall and this nitrogen-fixing cover crop feeds your soil straight through to spring.
Full sun
Every 7–14 days
180–240 days
USDA 4–8
Overview
Hairy vetch is a cool-season legume grown mostly as a cover crop and green manure rather than for looks. It sprawls into a vine-like mat of fine, feathery leaves and climbs whatever it can reach, which is why growers so often pair it with cereal rye for support. Come spring it throws up violet-purple to blue-purple flowers before the stand is cut down.
Its real job is in the soil. As a legume it teams up with Rhizobium bacteria to pull nitrogen out of the air and store it in root nodules, then releases that nitrogen when the plant is terminated and breaks down. A good stand of hairy vetch can supply much of the nitrogen a following corn crop needs.
The plant earns its keep, but it comes with two cautions. It is hard-seeded and reseeds freely, so it can turn into a weedy volunteer if you let it set seed. And unlike easygoing clover, heavy grazing can poison cattle and horses, so this is a soil 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 it in fall, leave it to fix nitrogen over winter, and cut it down at flowering before it sets seed.
Light
Hairy vetch does best in full sun and will take partial sun without much complaint. More light means a denser stand and more nitrogen fixed, so give it an open site where you can.
Water
Once established it shrugs off dry, well-drained soil and leans on fall, winter and spring moisture, so you rarely need to water it outdoors. What it will not tolerate is waterlogging, which invites crown and root rot.
Soil
It grows on well-drained sandy to loam soils and puts up with low fertility and some acidity, preferring a pH of 6.0 to 7.5. It asks for little nitrogen but does want enough phosphorus, potassium and sulfur to thrive.
Temperature
This is a tough cool-season plant, hardy through cold from about -20°F to 75°F (-29°C to 24°C). That winter hardiness is exactly why it works as an overwintering cover crop across zones 4 to 8.
Humidity
Ordinary outdoor humidity suits it fine, so there is no target to hit. Air movement matters more here, since a crowded, damp stand is what lets crown rots take hold.
Feeding
As a legume it feeds itself, fixing its own nitrogen through Rhizobium nodules, so skip the nitrogen fertilizer entirely. Inoculate the seed properly and make sure the soil has enough phosphorus, potassium and sulfur instead.
Pruning
Grown as an ornamental it needs no pruning. As a cover crop the equivalent step is termination, mowing, rolling or crimping at flowering, or tilling it in, before the plant sets mature seed so it releases nitrogen and does not reseed.
Repotting
none
Size & spacing
A stand reaches 3 to 12 feet (90 cm to 3.7 m) of trailing growth, with each plant spreading about 2 to 6 feet (60 to 180 cm) as it scrambles over its neighbors. Sown thickly as a cover crop, it knits into a dense mat rather than standing as separate plants.
When to plant
Hairy vetch runs on a fall-to-spring clock. Sow it about 30 to 45 days before the killing frost so it roots before winter, let it idle through the cold, and terminate the stand when it flowers in spring to release its nitrogen and head off 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
Most hairy vetch trouble traces back to three things: seed that reseeds, a stand that never got going, and wet-soil rots or spring aphids. Read the signs below and you can fix the cause rather than chase the symptom.
Vetch keeps coming back as a weed in later crops
This is hard-seed reseeding, the main downside of letting a stand mature. About 10% to 20% of the seed is hard-coated and can sit dormant in the soil for a season or more, then sprout in your next grain or vegetable crop and creep into field edges. Terminate the stand at flowering before any seed forms, and cultivate or spot-treat the seedlings that do appear before they flower.
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
Thin, pale stand with little nitrogen to show for it
Most of the time this comes down to failed inoculation. Without the right Rhizobium on the seed, few nitrogen-fixing nodules form and the plants stay yellow and weak. Sowing too late, poor seed-to-soil contact, waterlogged ground, or short phosphorus, potassium and sulfur all make it worse. Dig a few roots and check for pink, active nodules, then inoculate with fresh vetch or pea Rhizobium, firm the seed in 30 to 45 days before killing frost, and fix any drainage problem.
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
Wilting plants, rotted crowns, or aphids on the shoots
Soggy ground invites root and crown rots such as Sclerotinia, which show up as soft, discolored tissue and white fuzzy growth at the base. Aphids are the other spring problem, clustering on tender new shoots and leaf undersides. Plant on well-drained ground, rotate away from legumes if rots build up, and let the lady beetles that vetch attracts keep the aphids in check.
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
For cats, dogs and people the growing plant is low risk, and the leafy foliage is fine for rabbits and birds in moderation. The seeds carry mild toxins, so keep them out of reach. The real warning is for grazing animals: heavy hairy vetch can cause fatal toxicosis and bloat in cattle and horses, so never let livestock graze pure or thick stands.
Toxic to
Horses · Livestock
Safe for
People · Cats · Dogs · Rabbits · Birds
Horses Caution
Grazing heavy vetch is the real worry. Horses can develop hairy vetch toxicosis, with fever, skin sores, hair loss and weight loss, and a lush legume stand can also bring on bloat.
Livestock Caution
Cattle face the same danger as horses. A diet heavy in hairy vetch can trigger fatal granulomatous toxicosis, with fever, dermatitis, alopecia and weight loss, on top of ordinary legume bloat, so never let stock graze pure or thick stands.
Cats Safe
The growing foliage is low risk. A cat that gnaws a lot of plant or, more likely, eats the seeds might get a brief upset stomach, but nothing serious.
Dogs Safe
Much the same as for cats. Chewing the leaves rarely does more than pass through, though a dog that gulps down seeds can end up with some vomiting or loose stool.
Rabbits Safe
The leafy growth is fine in moderation as part of a mixed forage. Keep the seeds out of reach, since they carry the plant's mild toxins.
Birds Safe
Foraging birds handle the foliage without trouble. The seeds hold mild toxins, so they are not a feed to offer on purpose.
People Safe
This is a field crop, not something you eat. The plant poses no real hazard to handle, though the raw seeds and sprouts contain L-canavanine and are not food.
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 few named selections show up in the seed trade, mostly bred for better winter survival and earlier spring maturity.
'Purple Bounty'
A cold-hardy release bred to survive northern winters and flower early, which lets you terminate the stand sooner in spring.
'Purple Prosperity'
A companion selection to 'Purple Bounty' that overwinters reliably and matures early for the same earlier spring termination.
Common vetch (Vicia sativa)
A related cover crop with larger seed and less cold tolerance than hairy vetch, and seeds that 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 grown one way, from seed sown straight into the ground, with the right inoculant making all the difference.
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
Hairy vetch grows from seed sown straight into the ground in late summer to fall, about 30 to 45 days before the killing frost, so it can settle in before winter. Inoculate the seed with the proper Rhizobium first, then drill it at roughly 15 to 20 lb per acre or broadcast 25 to 30 lb per acre, often mixed with cereal rye for support. The stand establishes in fall, idles through winter, and takes off again in spring when the weather warms.
Myths
Vetches and legume cover crops are harmless grazing, just like clover.
Hairy vetch is a fine nitrogen-fixing cover crop, but it is not the easy forage clover is. Its seeds carry L-canavanine and, in some vetch seed, cyanogenic compounds, and heavy grazing can cause hairy vetch toxicosis, a systemic granulomatous disease, along with bloat in cattle and horses. Treat it as a soil crop, not safe pasture.