Coronilla varia aka Crownvetch

Coronilla varia, or crown vetch, belongs to the pea family. It is a perennial herb that spreads across the ground. Kew places its native range from Europe to Iran and Turkmenistan. It grows in dry grassland, along roads, and on railway banks. The RHS also lists it under the name Securigera varia. It loses its leaves in winter.

Plants reach about 1–3.3 feet [0.3–1 metre] in height. Their stems trail along the ground or rise above it. Grooves run along the angular stems, which lack most hairs. Green, pinnate leaves give the plant a fine texture. Each leaf has many small leaflets arranged in opposite pairs. The leaflets have smooth edges and rounded ends. Tough roots and spreading rhizomes help it form dense mats. Seeds also help it spread beyond the original planting.

Pink and white pea-shaped flowers grow in round clusters. Each cluster holds roughly ten to twenty-five small flowers. The RHS gives a flowering season from May to July. North Carolina State reports blooms from early summer into fall. Bees visit the flowers and help the plant set seed. The fruit is a narrow, angular pod with several segments. Pinched joints divide these segments, and a pointed tip ends the pod.

Crown vetch grows best in sun and well-drained soil. It also tolerates some shade and survives drought. Clay, loam, sand, and chalk all suit it. It accepts acid, neutral, and alkaline soils, including poor ground. It fixes nitrogen and needs little or no fertilizer. North Carolina State lists USDA zones 3–7. The RHS gives it a UK hardiness rating of H7. Growers can raise it from seed, cuttings, or divisions. Cutting it back can limit growth and make it bushier.

People have used crown vetch to cover slopes and reduce erosion. Its flowers also provide food for visiting bees. But its fast spread can crowd out nearby plants. It has become invasive in parts of the United States. Established patches can be hard to remove. Few major pests or diseases trouble it; spread is the main concern. PFAF records insecticide use and past medicinal use, but no known food use. The plant contains the toxic glycoside coronillin. Eating large amounts can cause paralysis or death. It poses a risk to people, pets, and horses. Its medicinal history does not make it safe to use.