Sea-kale

How to recognise it

Growth habit

Robust, hairless perennial, 40–75 cm tall and up to 1 m wide, forming a broad, rounded clump. The whole plant is covered with a bluish, waxy bloom.

Leaf

Large, often 30 cm or longer, thick and fleshy, blue-grey, on long stalks. The edge is lobed, wavy and curled. It looks like a cabbage leaf, but coarser and greyer.

Flower

White flowers about 1 cm across with four petals in a cross and yellow anthers, in large, broadly branched clusters above the leaves. They smell of honey and appear in May–June, sometimes into July.

Fruit/Seed

A hard, round fruit about 1 cm across on a short stalk, holding a single seed. When ripe it is dry and corky: it floats and is spread by the sea.

Roots

A thick, deep taproot with fleshy side roots, which anchor the plant in loose shingle and sand and draw water from deep down.

Confusion with

Cabbages have yellow flowers and long, narrow seed pods. Sea rocket grows on the same beaches, but it is a small annual with lilac flowers and narrow, fleshy leaves.

Flowering: May–July · Pruning: July and November

Why grow it?

• A rare native coastal plant that stays in the same spot in a garden for many years.
• The honey-scented flowers in May–June attract honeybees, bumblebees, solitary bees and hoverflies.
• The thick, blue-grey leaves with their wavy edges catch the eye from spring to autumn in a gravel garden or border.
• Food plant for the caterpillars of the large and small white butterflies, like most members of the cabbage family.
• An edible perennial: blanched shoots in spring, young leaves and flower buds later in the season.
• Copes with wind, salt and drought: ideal for a seaside garden or a dry, sunny spot inland.

Sea-kale: where does it grow best?

• In the wild: shingle and shell beaches, strandlines with washed-up seaweed and the foot of young dunes, where salt and wind keep competition low.
• In the garden: full sun, in an open, airy spot.
• Deep, free-draining soil: sand, gravel or sandy loam, ideally limy to neutral. It does not tolerate wet feet in winter.
• Lovely in a gravel or seaside garden, or in a permanent spot at the back of the vegetable plot, where it can stay undisturbed for years.

Goes well with

• Sea holly: A silvery-blue coastal plant for the same dry, sunny, sandy soil.
• Thrift: Pink cushions of flowers at its feet, also a true coastal plant.
• Yellow horned-poppy: Blue-grey leaves and large yellow flowers; a plant of the same shingle beaches.
• Asparagus: Another perennial vegetable for a permanent spot in the kitchen garden.

Sea-kale: when and how to plant it?

1. Buy seed or plants from a native plant nursery or a seed supplier specialising in heritage vegetables. Never take plants, roots or seed from the wild: sea-kale is very rare here.
2. Sow in March–April in small pots or a seed tray, 2 cm deep. The seed germinates faster and more evenly if you first carefully remove the hard, corky fruit case.
3. Plant out young plants or root cuttings in March–April, when the soil is no longer frozen or waterlogged.
4. Give each plant about 60 cm of space; in the vegetable garden, plant in rows 45–60 cm apart.
5. Improve heavy soil with coarse sand or gravel. In the vegetable garden a spadeful of compost is welcome; in a nature garden it is not needed.
6. Water after planting and keep the soil slightly moist for the first few weeks; after that, watering is rarely needed.

Care

Water

Only young plants in dry spells. An established plant draws enough water from deep down with its taproot, even in dry summers.

Feeding

Not needed in a nature garden. If you want to harvest it as a vegetable, give a thin layer of compost in spring: it gives thicker shoots.

Blanching

In January–February, place a bucket or forcing pot over the dormant plant. In the dark the shoots grow pale and tender; harvest them in March–April when they are 15–20 cm long.

Rest after harvest

Remove the pot after harvesting so the plant can grow for the rest of the year and regain its strength. Do not harvest in the first two years.

Flower stalks

If you mainly want leaves and shoots, cut the flower stalks off after flowering. For the insects and the seed, leave a few standing.

In the kitchen

Blanched shoots are briefly boiled or steamed, like asparagus. Young leaves are used like kale, the flower buds like broccoli.

Tip: Grow two or three plants if you want to harvest: then you can blanch one plant each year and let the others rest. A layer of gravel or shells around the crown keeps it dry in winter.

Pruning and mowing

Pruning months: July and November.

When: After flowering, in July, for the flower stalks, and in November for the dead leaves.

How:

• Cut spent flower stalks just above the leaves if you do not want seed, or leave a few to ripen.
• In autumn, remove yellowing and dead leaves: they attract slugs and can rot.
• Cut blanched shoots with a sharp knife just above the crown, leaving the buds in the centre.
• Always leave the crown itself alone: that is where next year’s buds are.

Caution: Never cut into the crown or the taproot, and never harvest from wild plants.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow in March–April or in autumn in pots of sandy soil. Remove the corky fruit case to speed up germination, which is often erratic.

Root cuttings

In autumn or winter, cut pencil-thick pieces of side root, 10–15 cm long. Cut the top straight and the bottom at a slant, so you know which end is up. Store them in damp sand and plant them upright in March, with the top just below the surface.

Sea-kale: how does it get through the winter?

Hardy to −20 °C.

• The leaves die back in autumn; the plant overwinters as a bare, thick crown on its taproot.
• Fully hardy, to about −20 °C. Wet, heavy soil is a bigger danger in winter than frost.
• January–February is the time to blanch: place a pot or bucket over the crown.
• Mark the spot with a cane so you do not accidentally dig up the dormant plant.

Diseases and pests

• Cabbage whites: The caterpillars of the large and small white eat the leaves. Pick off eggs and caterpillars or use fine insect mesh; on a large, healthy plant a little damage is no problem.
• Flea beetles: Tiny jumping beetles make small holes in young leaves in spring. Keep the soil slightly moist; older plants simply grow away from it.
• Slugs: They love the young, blanched shoots. Check under the forcing pot regularly and remove them by hand.
• Clubroot: A soil disease of the cabbage family that makes the roots swell. Do not plant sea-kale where cabbages with clubroot have grown; limy, free-draining soil helps.
• Pigeons: Wood pigeons peck at the leaves in winter and spring. A net over young plants helps.

Through the year

• January: Place a forcing pot or bucket over the dormant crown.
• February: Blanching. Store root cuttings in damp sand.
• March: Harvest blanched shoots. Sow and plant root cuttings.
• April: Last harvest, then remove the pot. Plant out young plants.
• May: Flowering begins: honey scent and lots of bees.
• June: Full bloom. Watch out for cabbage white caterpillars.
• July: Last flowers. Cut off flower stalks or leave them for seed.
• August: The fruits ripen. Water young plants in dry spells.
• September: Collect ripe seed.
• October: Sow in pots outdoors. Take root cuttings.
• November: Remove dead leaves. Mark the spot with a cane.

Did you know?

• The genus name Crambe comes from the Greek krambē, an old word for cabbage.
• The corky fruits float in seawater and can be carried by currents to new beaches.
• On the English coast, people used to harvest the shoots that grew up pale through the shingle. In the 18th and 19th centuries sea-kale became a popular vegetable there, grown under special forcing pots.