Crambe cordifolia aka Colewort

Crambe cordifolia is a large perennial in the cabbage family. Gardeners call it colewort or greater sea kale. Kew places its native range in the North Caucasus. It forms a broad clump and loses its leaves in winter. Its bold leaves and tall flowers need plenty of room.

The leaf mound reaches about 1.5 feet [0.46 metres] high. Large green leaves have deep lobes and a crinkled surface. They can reach about 1 foot [0.3 metres] across. Strong, branching stems rise well above this low mound. Flowering stems usually reach 4–6 feet [1.2–1.8 metres]. Missouri Botanical Garden records occasional heights of 7 feet [2.13 metres]. RHS gives a broader height range of 4.9–8.2 feet [1.5–2.5 metres]. Clumps spread about 3.3–4.9 feet [1–1.5 metres] wide.

Small white flowers grow in loose sprays above the leaves. Each flower has four petals and a sweet scent. June to July is the main flowering period listed by Missouri Botanical Garden. Its account puts the flower display at about three weeks. The plant suits sunny borders, cottage gardens, and wild gardens. Its size makes it useful as a bold border accent. Large clumps can also serve as ground cover. RHS lists the flowers for cutting.

Give it deep, fertile soil that drains well. Full sun suits it best, though it accepts partial shade. RHS also notes that it can grow in poor soil. It accepts acid, neutral, and alkaline conditions. Keep soil moderately moist to help the leaves stay sound. Dry soil can cause leaf decline and scorch in heat. Hot, humid summers in the deep South do not suit it. Shelter it from strong winds, and stake flowering stems as needed. Leave established tap roots undisturbed. Cut dead growth to ground level in autumn. Hardiness ratings are USDA zones 5–8 and RHS H5.

Slugs, flea beetles, and caterpillars may damage the leaves. Club root is another possible problem. Plants For A Future lists cooked leaves and roots as food. Young leaves taste like cabbage; older leaves become tough. That source reports no known hazards, rather than proof of safety. It also records traditional use for itch, without evidence of effectiveness.