Identification: The Rugged Nitrogen Engine
Hairy Vetch (Vicia villosa) is a sprawling, vining herbaceous legume that is a biological engine for soil regeneration. It is a winter annual that typically reaches 3 to 6 feet in length, relying on branched tendrils at the leaf tips to climb surrounding vegetation.
Visual Markers: The stems and leaves are covered in a dense, soft, silvery-white pubescence (hairs). The leaves are pinnately compound with 10-20 leaflets. Flowers appear in late spring as vibrant purple clusters (racemes) on one side of the stem.
Habitat and Range
Highly resilient and winter-hardy, thriving in **USDA Zones 7 and 8**. It prefers well-drained sandy loams but is famous for its ability to grow in nutrient-depleted, acidic soils where other legumes fail.
Ecological Role
A premier nitrogen-fixer, contributing up to 200 pounds of nitrogen per acre. It provides significant nectar for bumblebees and cover for small wildlife.
Toxicity and Animal Interaction
SIGNAL WORD: WARNING
Risk Exposure Level: High (Systemic Disease). Ingestion of mature Hairy Vetch can cause a fatal immune-mediated disease in cattle and horses. The seeds are also toxic if ingested.
Veterinary Response Notes
Remove from source immediately if skin lesions or milk drop occur. **Reference:** Merck Veterinary Manual, "Pyrrolizidine Alkaloid Toxicosis." [General Gardening Tips](/tech-lab/gardening-basics)