Hairy Vetch
Vicia villosa · legumes
Hairy Vetch (Vicia villosa) is an annual in the legumes.
When do I plant this? →
Plan this in your garden →
What the corpus records
- Mature height
- 30–91 cm12–36 in
- Mature spread
- 30–91 cm12–36 in
- Days to maturity
- 70–100
- Light
- Part sun
- Feeding
- Makes its own nitrogen
- Root depth
- Medium
- Frost tolerance
- Hardy
- Lifespan
- Annual
- Habit
- Vine
- Value to pollinators
- Moderate
- Fixes nitrogen
- yes
Which of these numbers are soft
Every number above carries a confidence tier. These are the ones the corpus does not stand behind — estimated from general knowledge, or contested between sources. They are shown because hiding them would be the dishonest half of showing the rest.
- days to maturity — estimated
- root depth — estimated
- frost tolerance — estimated
- casts shade — estimated
- ground coverage — estimated
- pollinator value — estimated
- bloom window — estimated
Rules that apply to Hairy Vetch
PromisingCold-hardy annuals can be sown or transplanted before the last spring frost — hardy crops about three weeks before, half-hardy about two weeks before. Tender crops wait for the frost itself.
suboptimal if ignored → advise
Mechanism: Cold hardiness. Hardy crops tolerate hard frost and half-hardy crops tolerate light frost, so they can occupy the ground weeks before frost-tender crops are allowed in. The offset is measured from the last spring frost.
Evidence: confirmed against 4 sources in the research-based literature.
the 4 sources
University of Illinois Extension, 'Time Your Vegetable Plantings by Cold Hardiness' (2018-03-26), extension.illinois.edu/blogs/ilriverhort/2018-03-26-time-your-vegetable-plantings-cold-hardiness: very hardy vegetables 'withstand freezing temperatures and hard frosts without injury' (planted earliest in spring); frost-tolerant vegetables 'can withstand light frosts, but not freezing temperatures' (planted a couple of weeks later). LLM-summarised from a read of the page; it establishes the CATEGORIES but states no week offsets.
Colorado State Univ. Extension, GardenNotes #720, 'Vegetable Planting Guide', extension.colostate.edu/resource/vegetable-planting-guide (read 2026-07-25): hardy vegetables go in 'As early as 2-4 weeks before the date of the average last spring frost'; semi-hardy 'As early as 0-2 weeks before the date of the average last spring frost'; tender from seed 'around the date of the average last spring frost'; very tender 'Typically 2+ weeks after'. This is the source that states the offsets in weeks.
Where this rule sits in that range: hardy at 3 weeks is mid-range of CSU's 2-4. Half-hardy at 2 weeks is the EARLIEST EDGE of CSU's 0-2 - the most aggressive planting CSU sanctions, not the middle of it. The rule is inside published guidance at both ends, but it leans early on the half-hardy side and a gardener following it in a cold spring is taking that boundary.
Do not import an offset from another publication's hardiness scheme without checking the category names: CSU has no 'very hardy' tier, so a '4-6 weeks before frost' figure written against a four-tier scheme does not describe CSU's 'hardy'. Categories are not comparable across sources.
Read the full rule → · open in the planner ↗
PromisingA legume fixes atmospheric nitrogen only in symbiosis with rhizobia specific to its cross-inoculation group; ground with no recent history of that group may carry too few of them to nodulate well.
suboptimal if ignored → advise
Mechanism: Nitrogen fixation happens in root nodules formed by Rhizobium or Bradyrhizobium bacteria specific to each legume group. On ground that has not grown that legume group before - a new bed, a soil-less mix, a long gap in the rotation, a fumigated or strongly acid soil - the matching strain can be absent or sparse, so nodulation and fixation are reduced until a population builds.
Evidence: confirmed against 1 source in the research-based literature.
the source
Penn State Extension, 'Inoculation of Forage and Grain Legumes', extension.psu.edu/inoculation-of-forage-and-grain-legumes (read 2026-08-14): 'Rhizobia bacteria are fairly specific as to which legumes they will infect, form nodules on the roots of, and for which they will fix nitrogen'; 'Legumes effectively nodulated by the same Rhizobia species are termed cross-inoculation groups'; 'Inoculation is recommended when the legume being planted has not been grown in that field in the past three years or with every planting of a high-value crop'; 'Inside the nodule, an enzyme called nitrogenase drives the N fixation reaction.'
remedy
On first-time legume ground, coat the seed at sowing with the inoculant matched to the crop's group (garden peas and beans, soybean, and clover each take a different one). Ground that has grown that legume recently usually needs none. It is a cheap one-time step - advised where the history is absent, never required.
Read the full rule → · open in the planner ↗
Another 91 rules in the corpus apply by situation rather than by species — rotation intervals, frost windows, sun, spacing and soil. Read the full evidence page.
Cite this page
Milpa Gardens. "Hairy Vetch (Vicia villosa)." https://milpa.garden/plants/vicia-villosa/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
All plants