Ornamental · Fabaceae
Hairy Vetch
Vicia villosa
Sow it in fall and this nitrogen-fixing cover crop quietly feeds your soil right through to spring.
Full sun
Every 7–14 days
180–240 days
USDA 4–8
Overview
Hairy vetch isn't grown for looks, and that's fine, because it's a cool-season legume that earns its keep as a cover crop and green manure. It sprawls out into a vine-like mat of fine, feathery leaves and grabs onto whatever it can climb, which is exactly why growers so often plant it alongside cereal rye to give it something to lean on. When spring rolls around, up come the violet-purple to blue-purple flowers, right before the stand gets cut down.
The real action, though, is underground. Being a legume, hairy vetch teams up with Rhizobium bacteria to grab nitrogen out of the air and stash it away in root nodules, and then it hands that nitrogen back once the plant's terminated and starts breaking down. Pretty handy, right? A good stand can cover a big chunk of what a following corn crop needs.
It pulls its weight, but there are two things to keep in mind. It's hard-seeded and reseeds without much fuss, 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 treat it as a soil crop first and a forage a distant second.
Care
The short version: it wants full sun, well-drained ground, and seed inoculated with the right Rhizobium. Sow it in fall, let it fix nitrogen all winter, and cut it down at flowering before it sets seed.
Light
Hairy vetch loves full sun, but it'll take partial sun without much grumbling. More light gets you a denser stand and more nitrogen fixed, so pick an open spot if you can swing it.
Water
Once it's settled in, it just shrugs off dry, well-drained soil and leans on fall, winter and spring moisture, so you'll hardly ever need to water it outdoors. The one thing it can't stand is waterlogging, which opens the door to crown and root rot.
Soil
It's happy on well-drained sandy to loam soils and puts up with low fertility and a bit of acidity, though it likes a pH of 6.0 to 7.5. It barely asks for nitrogen, but it does want enough phosphorus, potassium and sulfur to really thrive.
Temperature
This is one 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 so well as an overwintering cover crop across zones 4 to 8.
Humidity
Ordinary outdoor humidity suits it just fine, so there's no number to worry about. What matters more here is air movement, since a crowded, damp stand is what lets crown rots move in.
Feeding
Being a legume, it feeds itself by fixing its own nitrogen through Rhizobium nodules, so you can skip the nitrogen fertilizer completely. Just inoculate the seed well and make sure the soil has enough phosphorus, potassium and sulfur.
Pruning
Grown as an ornamental, it needs no pruning at all. As a cover crop, the equivalent move is termination, so you mow, roll or crimp it at flowering, or till it in, before it sets mature seed, which lets it release nitrogen and skip the reseeding.
Repotting
none
Size & spacing
A stand climbs to 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 clambers over its neighbors. Sow it thick as a cover crop and it weaves into a dense mat instead of standing around as separate plants.
When to plant
Hairy vetch runs on a fall-to-spring schedule, and it's easy to follow. Sow it about 30 to 45 days before the killing frost so it roots before winter, let it coast through the cold, and then terminate the stand when it flowers in spring to release its nitrogen and keep it from 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 headaches boil down to three things: seed that reseeds, a stand that never really got going, and wet-soil rots or spring aphids. Read the signs below and you'll be fixing the actual cause instead of chasing the symptom around.
Vetch popping up as a weed in your next crop
So what's going on here? It's hard-seed reseeding, and it's the price you pay for letting a stand go to maturity. About 10% to 20% of the seed has a hard coat, so it can nap in the soil for a season or more and then wake up in your next grain or vegetable crop, and even wander into the field edges. The fix is easy enough: cut the stand at flowering before any seed forms, and then cultivate or spot-treat whatever seedlings do sneak through, well 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 that isn't giving you much nitrogen
Nine times out of ten, this is failed inoculation talking. If the right Rhizobium isn't on the seed, hardly any nitrogen-fixing nodules form, and the plants just sit there yellow and weak. Sowing too late, loose seed-to-soil contact, soggy ground, or being short on phosphorus, potassium and sulfur can all make it worse too. Dig up a few roots and see if you've got pink, active nodules, then inoculate with fresh vetch or pea Rhizobium, firm the seed in 30 to 45 days before killing frost, and sort out any drainage trouble.
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, rotting crowns, or aphids showing up on the shoots
Soggy ground is usually the culprit behind root and crown rots like Sclerotinia, which you'll spot as soft, discolored tissue and white fuzzy growth down at the base. Then there are aphids, the other spring headache, bunching up on tender new shoots and the undersides of the leaves. The good news? Plant on well-drained ground, rotate away from legumes if the rots start piling up, and let those lady beetles vetch brings in do the aphid patrol for you.
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 rabbits and birds do fine with the leafy foliage in moderation. The seeds carry mild toxins, so just keep them out of reach. The one big warning? It's 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 thing to really watch. Horses can come down with hairy vetch toxicosis, which brings fever, skin sores, hair loss and weight loss, and a lush legume stand can also set off bloat.
Livestock Caution
Cattle are looking at the same danger horses face. Load their diet up with hairy vetch and you can trigger fatal granulomatous toxicosis, with fever, dermatitis, alopecia and weight loss, plus the usual legume bloat, so never let stock graze pure or thick stands.
Cats Safe
The growing foliage? Pretty much low risk. If a cat chews down a lot of plant, or more likely gets into the seeds, it might get a quick upset stomach, but that's about the worst of it.
Dogs Safe
Dogs are in the same boat as cats. Chewed-up leaves usually just pass right through, though if a dog wolfs down a bunch of seeds, you might see some vomiting or a loose stool.
Rabbits Safe
A bit of the leafy growth is fine as part of a mixed forage, no problem there. Just keep the seeds out of reach, since they carry the plant's mild toxins.
Birds Safe
Foraging birds handle the foliage just fine. The seeds do hold mild toxins though, so they aren't something to put out on purpose.
People Safe
This one's a field crop, not dinner. There's no real hazard in handling it, but the raw seeds and sprouts contain L-canavanine, so they're definitely 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
You'll only find a handful of named selections in the seed trade, and they're mostly bred for better winter survival and an earlier spring maturity.
'Purple Bounty'
This one's a cold-hardy release bred to make it through northern winters and flower early, so you can terminate the stand sooner in spring.
'Purple Prosperity'
It's a companion to 'Purple Bounty' that overwinters reliably and matures early too, which gets you that same earlier spring termination.
Common vetch (Vicia sativa)
This is a related cover crop with bigger seed and less cold tolerance than hairy vetch, and its seeds come with 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
There's really just one way to grow hairy vetch, and that's from seed sown straight into the ground, where the right inoculant ends up 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
Growing hairy vetch is refreshingly simple. You just sow the seed right into the ground in late summer to fall, about 30 to 45 days before the killing frost, so it can settle in before winter shows up. Coat 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, and a lot of folks toss in cereal rye for support. The stand roots in fall, coasts through winter, and then really takes off in spring once things warm up.
Myths
Vetches and legume cover crops are harmless grazing, just like clover.
It's tempting to think vetch grazes as easily as clover, but it really doesn't. Hairy vetch is a great nitrogen-fixing cover crop, sure, yet its seeds carry L-canavanine and, in some vetch seed, cyanogenic compounds, and heavy grazing can cause hairy vetch toxicosis, a systemic granulomatous disease, plus bloat in cattle and horses. Think of it as a soil crop, not safe pasture.