Crambe maritima aka Sea Kale

Crambe maritima, or sea kale, belongs to the mustard family. This herbaceous perennial grows on coasts from Europe to the Caucasus. Its range includes Britain and Ireland. Wild plants grow on sand, shingle, rocks, and sea cliffs. They often grow near the line of washed-up shore debris. In gardens, sea kale serves as both a vegetable and an ornamental plant.

The plant forms a broad clump of leaves at ground level. Garden plants reach about 2.5–3 feet (0.75–0.91 metres) tall. They spread about 2–2.5 feet (0.61–0.76 metres) wide. RHS gives a wider height range, reaching 3.3 feet (1 metre). Its listed spread is smaller than the Missouri Botanical Garden range. The large, fleshy leaves have a blue-green, waxy surface. Their edges wave and curl, with shallow lobes. Individual leaves can reach 2 feet (0.61 metres) long. The foliage dies back for winter.

Thick stems hold dense clusters of small white flowers. These rise above the leaves and have a scent. The broad flower clusters can span 2 feet (0.6 metres). Bloom dates differ among the garden sources. Chicago lists May to June; Missouri lists June to August. The flowers draw butterflies, and Chicago reports resistance to deer. The leaves provide much of the plant's garden interest. Sea kale suits borders, gravel beds, and cottage gardens. It also works in coastal gardens, vegetable beds, and containers. Groups of plants can provide ground cover.

Give sea kale full sun and soil that drains well. It tolerates some shade and poor soil. Rich, sandy or gravelly loam supports good growth. Missouri favours neutral to alkaline soil; RHS also accepts acid soil. Keep soil moderately moist, though established plants withstand some drought. RHS advises shelter from strong winds. Missouri lists USDA zones 5–9; Chicago extends the range to 4–9. RHS rates it H7 for severe winter cold. Plants can take two to five years to mature. Propagate by seed, division, or root cuttings. Cut the old growth to ground level in autumn.

Slugs and caterpillars can damage sea kale, and clubroot may occur. Missouri reports no major pest or disease problems overall. Young leaves and spring shoots can be eaten raw or cooked. Older leaves taste more bitter. Gardeners blanch shoots before cooking them like asparagus. Flowers are edible, and roots can be cooked. PFAF records no known hazards and no known medicinal uses.