Crambe, sea kale: planting, growing and care

Description and botany

Crambe is an herbaceous perennial plant of the family Brassicaceae, formerly the crucifers, a wild cousin of the cabbages in our vegetable gardens. Depending on the species, it originates from the Caucasus, temperate zones of Europe, the Canary Islands or Central Asia.

Around twenty annual or perennial species are recognised but only a few are cultivated, such as Crambe maritima — also called cordate crambe, “sea kale” or “sea cabbage” — which is edible and grows naturally in sandy and stony coastal areas of the Atlantic, the North Sea and places such as the Morbihan. Long harvested for food, this delicious yet forgotten sea kale has become quite rare and is now strictly protected.

You will also find Crambe cordifolia, nicknamed “cloud kale”, which is more ornamental for its imposing, spectacular foliage and flowering: this cabbage deserves better than a place between two rows of vegetables! There is also Abyssinian crambe (Crambe hispanica).

Crambe grows in clumps from a thick, woody crown with deep roots. It can reach about 70 cm in height for Crambe maritima whereas Crambe cordifolia can easily reach up to 2 m in flower, with an equal or greater spreading in each case. Somewhat slow to establish, Crambe needs around two to three years to bulk up and show its true dimensions.

A slow grower matched only by its longevity, it can live for over 10 years and sometimes up to 20 years!

Foliage varies by species. Evergreen in Crambe maritima, it is deciduous in Crambe cordifolia.

Crambe maritima – botanical illustration

Sea kale produces long petioles bearing numerous rounded, fleshy leaves, very undulate or even ruffled at the margins, 30 to 50 cm long. Glaucous, covered with a bluish bloom, they resemble garden cabbage leaves; the young leaves are edible (as are the roots).

The foliage of Crambe cordifolia is truly magnificent. It differs from sea kale by its size and its large basal, heart-shaped (cordate) leaves reaching 40 to 60 cm in length and width. They are thick, fleshy, brittle and pubescent. Heavily wrinkled and dentate, dark bluish-green, they unmistakably recall the leaves of garden crucifers. The leaves arranged higher up the stems are smaller, ovate and hairless. Basal foliage often disappears quickly after flowering, often as early as September, while the attractive growth of Crambe maritima persists through winter.

In crambes, the airy, scented flowering appears in spring from May to July depending on climate. Spectacular, the flowering of Crambe cordifolia gives this large perennial the appearance of a giant gypsophila. It differs from sea kale by its profusion of blooms, earning it the poetic nickname “cloud kale”. Not without interest, the sea kale’s flowering is nonetheless less spectacular due to the more modest development of that species.

The very airy flower stalks sometimes reach over 1.80 m and bear large, light but dense, highly branched panicles composed of countless downy balls that open into small 1 cm flowers made of 4 sepals. Ivory white, sometimes tinged with pink, these mossy pom-poms suspended in the air evoke flowers of gypsophila, meadow-rue or even mimosa. This fleeting floral mist gives off a pleasant sweet scent reminiscent of honey.

Nectariferous, these tiny flowers attract many pollinating insects, including bees.

Each pollinated flower gives way to globose fruits, round, hard siliquas that turn yellow at ripeness and contain seeds that readily self-seed.

Hardy to around -15/-20°C, crambe is quite easy to grow in sun in deep, strictly well-drained soil, including calcareous or stony soils that retain some coolness at depth. Crambes fit well into natural gardens, romantic gardens and gravel gardens where they add an airy relief. Tolerant of sea spray, sea kale is a good choice for a seaside garden. Do not confine it to the vegetable patch; like its larger relative cloud kale, it will also make a strong impression in an ornamental border, in rocky beds that are not too dry. With its extrovert character, cloud kale will find its place as a specimen or in the centre of a large flower bed.

Superb airy flowering of Crambe cordifolia

All parts of sea kale are edible; sliced leaves and flower buds dress salads, roots can be cooked, and especially the young shoots which, after blanching, recall the flavours of cardoon, asparagus and cauliflower.

Main species and varieties

Although there are around twenty Crambe species, only a few are cultivated. Species such as Crambe cordifolia and sea kale (Crambe maritima), valued for their edible shoots, will easily find a place in the garden, in rockeries that are not too dry, and are also appreciated for their ornamental appeal. Both form very long-lived, fragrant clumps.

Most popular

Crambe maritima - Sea Kale

As beautiful as it is tasty! This cabbage forms attractive clumps with edible bluish-green leaves and an airy, fragrant white flowering. A worthy addition to the garden for visual pleasure, and also to a curious gardener's vegetable patch.

• Flowering time June to August
• Height at maturity 60 cm

See the full description

Our favourites

Crambe cordifolia - Greater Sea Kale

Imposing yet airy, this perennial cabbage stands out in ornamental garden with large fleshy leaves topped by a white, scented flowering at head height. Prefers full sun in large flower borders!

• Flowering time June to August
• Height at maturity 1,80 m

See the full description

Crambe cordifolia - Flowering Sea Kale Seeds

A very elegant perennial cabbage that forms a true cloud of small white flowers scented with honey. It will add a touch of poetry to planting scenes.

• Flowering time June to August
• Height at maturity 1,80 m

See the full description

Planting

Where to plant Crambe?

With very good hardiness, Crambe grows almost everywhere in France, tolerating temperatures down to at least −15 to −20°C in well-drained soil. Cultural requirements vary slightly according to species. However, all crambes are perennials that require sun and soil deep enough to root well.

A plant of the seaside, sea kale favours mild, humid climates and tolerates sea spray well, making it a good plant for coastal gardens. It does not tolerate drought well. It prefers stony, even calcareous sites, and above all very well-drained soils that remain cool at depth. It will be perfect with vegetable garden plants, of course, but also in the ornamental garden in sunny rockeries that are not too dry, in wall crevices, in a gravel bed or in a mixed-border.

Crambe cordifolia will need a position protected from strong winds that could break its tall stems and, while it tolerates poor soil, it will reach its full potential in more fertile soil.

Both dislike heavy, winter-wet, poorly drained soils in which their collar is likely to rot.

Give greater sea kale a well-exposed position, as it dislikes overcrowding and root competition: therefore leave enough space for it to develop freely. Place it in the middle or at the back of large beds of somewhat heavy perennials, where its opulent yet airy flowering lightens the composition.

All crambes will bring a delicate, airy texture to natural or naturalistic gardens or romantic ones.

Crambe cordifolia

When to plant crambes?

Planting crambes is preferably done in spring, from February to April, after frosts, or in autumn, from September to November.

How to plant crambe?

In open ground

In heavy soils: add river sand or gravel to lighten the soil. Favour a well-aerated planting for Crambe cordifolia; moreover this species will be more floriferous in fertile soil: add a few handfuls of compost to garden soil. Once well rooted, crambe does not like to be disturbed; transplanting is not recommended.

Crambes are very airy perennials that benefit from being planted in large clumps for a spectacular effect, counting 5 plants per m² for sea kale, spaced at least 40 to 70 cm apart, and 1 plant per m² for greater sea kale, which is much more imposing.

• Dig a hole 2 to 3 times the volume of the rootball
• Dig over the soil deeply
• Make a 20 cm deep gravel bed at the bottom of the hole
• Mix river sand half-and-half with the excavated soil
• Plant without burying the collar
• Fill in the planting hole
• Firm the soil lightly with your hand
• Water regularly after planting and mulch

When and how to sow Crambe cordifolia and Crambe maritima ?

Sow Crambe seeds in February–March under cover or directly in open ground in April–May. If you already had a Crambe in your garden, you may have kept some seed pods to use for your sowings and obtain new young plants (note: in that case they need stratification before sowing); otherwise choose from our Crambe seeds.

In seed tray

• Sow Crambe seeds broadcast in a seed tray or in small trays filled with potting compost mixed with sand
• Cover seeds with a 5–6 mm layer of potting compost
• Firm gently
• Keep potting compost moist but not waterlogged at 15–18 °C until germination, which usually occurs between 3 and 5 weeks
• Prick out strongest seedlings into small 7.5 cm buckets
• Plant out when young plants reach about 10 cm (when at the 5–6 leaf stage) and when risk of frost has passed
• Protect young seedlings from slugs

In open ground

You can also sow Crambe seeds directly in open ground in April–May in well-prepared, light and perfectly free-draining soil.

• Clear site thoroughly and loosen soil deeply
• Add leaf mould and coarse sand
• Sow in small groups of 2–3 seeds
• Cover with potting compost
• Water sowings regularly during emergence
• Thin out to at least 50 cm spacing, more for Crambe cordifolia

Succeed in sowing perennials, it’s easy if you follow our advice!

Striking graphic foliage of sea kale

Maintenance, pruning and care

Undemanding, crambe is easily grown without requiring much attention.

Water regularly, but never waterlog the soil, during first summer following planting to encourage establishment. Once well established, it will only need watering in case of prolonged drought. Mulch with a dry mulch (straw, flax shives) to retain soil freshness.

The Greater sea kale is more demanding than sea kale: each spring add compost by lightly forking around its base.

Cut off faded flower stalks to prevent them going to seed (unless you wish to collect seed for sowing, in which case keep a few as seed-bearers). Remove old damaged and dry foliage and cut back clump of Greater sea kale after flowering.

If you grow sea kale as a vegetable, we recommend removing the flowers to encourage leaf formation and blanching them as with endives so they lose all bitterness: one month before harvest of petioles, cover your young plants with a terracotta pot or cloche.

Harvest, uses and storage of sea kale

Be patient, it will take three years before harvesting first shoots. Their flavour is a subtle blend of asparagus, cardoon and cauliflower. Although all parts of Crambe maritima are edible, it is mainly the petioles and leaves that are used in cooking.

When to harvest sea kale?

Evergreen leaves are picked as needed, throughout the year. Young shoots, meanwhile, are harvested before flowering, from February–March to April after being blanched beforehand.

How to cook sea kale?

Young leaves can be eaten raw, finely sliced in salad or cooked in water or steamed like endives or asparagus, served with vinaigrette, in a gratin or as a soup. Flower buds can be enjoyed raw or cooked.

Greeks and Romans in Antiquity ate lacto-fermented leaves as sauerkraut.

Potential diseases and pests

When planted in well-drained soil, crambe is long-lived and fairly disease-resistant. It dislikes excess water and gastropods when shoots emerge.

Protect young shoots from snails and slugs: follow our advice to control gastropods!

As with all brassicas, crambe foliage can be devoured by flea beetles and cabbage whites: spray a decoction of tansy leaves, dislodge pests by regularly spraying the foliage.

Cabbage white caterpillar

Excess water in soil encourages rotting of stems or collar: ensure soil is well drained.

Multiplication

Crambe multiplies by clump division in spring or autumn on a plant 4 or 5 years old, or by sowing from March to June. Root cutting is also possible in autumn on a young plant already well established.

Clump division

• Using a digging fork, lift the clump
• Divide into several pieces, each with at least two buds
• Replant immediately in well-worked, free-draining soil

Root cuttings

• Take 10 cm sections containing roots and buds
• Insert them into buckets filled with potting compost and river sand
• Water regularly
• Keep protected from frost
• Transplant to ground the following spring when cutting has sufficient roots

Sowing

Sowing takes place in spring using fresh Crambe seeds from the year, harvested as soon as they turn yellow, or with our crambe seeds sold in easy-to-sow sachets. Germination is sometimes slow and erratic. Proceed according to the method shown in our section «When and how to sow crambe cordifolia and crambe maritima?».

Companion planting with crambe in the garden

With their airy flowering and fleshy blue‑green leaves, heart‑shaped on the cloud cabbage, Crambe plants bring breath, exuberance and lightness to the garden, transforming a simple perennial border into a grand and poetic tableau. They are the charm of English cottage gardens, country gardens or seaside gardens, where they compose opulent and romantic summer scenes. They also find their place easily in a white garden.

Sea kale is spectacular in the vegetable patch as well as in the ornamental garden, although the strong personality of the cloud cabbage makes an even greater impression!

An idea for a pairing in a range of tangy yellow‑green, orange and white: Euphorbia characias ssp wulfenii, Crambe maritima, Euphorbia polychroma, Erysimum ‘Rysi Copper’ and Iris sibirica ‘Snow Queen’

They are easy to combine, fitting effortlessly into natural, abundant scenes. Depending on species, Crambe can play the dazzling role of a mid‑ or back‑of‑border plant creating a luminous floral mist, or a mossy foreground for mixed-border.

As Crambe is slow to settle and, once established, its foliage quickly fades after flowering and becomes rather untidy, it is better to hide its base with some bushy perennials such as hardy geraniums ‘Rozanne’, salvias, dianthus, groundcover roses or annuals such as white cornflowers, ornamental carrot, lobelias or nicotianas which will also keep the base cool and fresh.

In a gravel bed, the sea kale will make an impression all year, remaining evergreen even in winter; combine it with perennials of exotic appearance such as agaves, graphic grasses like carex or other perennials with evergreen foliage such as wormwoods, creeping bugles or lamb’s ears, sedums or white delosperma, in harmonies of white and silvery tones.

In generous yet delicate compositions, pair the giant sea kale with the light flowers of Cosmos, Armeria maritima, gauras, asters and Gypsophilas. It will thrive in a community alongside vigorous perennials or other giant, airy plants that will either precede or follow its flowering, such as Delphiniums, Echinops, Digitalis, Eragrostis spectabilis, Thalictrums or hollyhocks. With Hostas, it will create lush borders.

Crambe complements admirably the glaucous foliage of Achillea millefolium, Euphorbias, nepetas and even lavenders.

→ More ideas for pairing with Crambe in our article.