<em>Crambe</em>, sea kale or nuage: to plant, to grow, to care for

Description and botany

Crambe is a herbaceous perennial plant of family Brassicaceae, formerly crucifers, a wild cousin of garden cabbage. Depending on species, it originates from Caucasus, temperate zones of Europe, Canary Islands or central Asia.

There are about twenty annual or perennial species but only a few are cultivated, such as Crambe maritima also called Crambe maritima, “sea kale” or “sea cabbage”, which is edible and which grows wild on sandy and rocky coastal areas of Atlantic coast, North Sea and Morbihan. Long harvested for food, sea kale, as delicious as it is forgotten, has become quite rare and is now strictly protected.

Crambe cordifolia is also found — Crambe cordifolia, nicknamed “cloud kale” — which is a species grown mainly for its imposing and spectacular foliage and flowering: this kale deserves more than a simple spot between two rows of vegetables! There is also Abyssinian crambe (Crambe hispanica).

Crambe develops in clumps from a thick woody stump deeply rooted. It can reach 70 cm in height for sea kale and easily up to 2 m in flower for Crambe cordifolia, with at least equivalent spread. A little slow to establish, Crambe needs around two to three years to bulk up and reach full potential.

A slow grower with impressive longevity, lifespan can exceed 10 years and sometimes reach 20 years!

Foliage differs by species. Evergreen for Crambe maritima, it is deciduous for Crambe cordifolia.

Crambe maritima – botanical illustration

Sea kale develops long petioles bearing numerous rounded and fleshy leaves, very undulate even curly at the margins, 30 to 50 cm long. Glaucous, covered with a bluish bloom, they resemble those of garden cabbages; young leaves are edible (as are the roots!).

Foliage of Crambe cordifolia is truly magnificent. It differs from sea kale by its breadth and its imposing basal leaves in the form of a heart (cordiform), reaching 40 to 60 cm in length and width. They are thick, fleshy, brittle and pubescent. Strongly crinkled and dentate, dark bluish-green in colour, they inevitably call to mind leaves of crucifers from vegetable gardens. Leaves set higher up the stems are smaller, ovate and hairless. Basal foliage disappears quickly after flowering, often by September, while attractive vegetation of Crambe maritima persists through winter.

In crambes, airy and scented flowering appears in spring from May to July according to climate. Spectacular, flowering of Crambe cordifolia gives this large perennial appearance of giant gypsophila. It differs from sea kale by its profusion, earning it the poetic nickname “cloud kale”. Less showy, sea kale nevertheless offers interest but its flowering is less spectacular due to more moderate development of that Crambe species.

Flower stems, very airy, can sometimes exceed 1.80 m and bear large, light but dense and highly branched panicles with countless fluffy 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 recall flowers of gypsophila, nigella or even mimosa. This evanescent floral mist gives off a pleasant sweet scent reminiscent of honey.

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

Each pollinated flower gives way to globose fruits, round hard siliquae turning yellow at ripeness and containing seeds that easily self-sow.

Hardy to -15/-20°C, Crambe is fairly easy to grow in sun in deep, imperatively well-drained soil, even calcareous or stony, provided it retains coolness at depth. Crambes fit easily into natural, romantic gardens and gravel gardens where they bring airy relief. Tolerant of sea spray, sea kale is a good choice for seaside gardens. Do not confine it to the vegetable plot; like its large cousin cloud kale, it also makes a strong impression in ornamental beds, on not-too-dry rockeries. With its extrovert character, cloud kale will better find its place as a specimen or in centre of a large flowerbed.

Superb airy bloom of Crambe cordifolia

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

Main species and varieties

Although there are about twenty Crambe species, only a few are cultivated. Crambe cordifolia and sea kale (Crambe maritima), prized for edible shoots, fit easily into garden rockeries that are not too dry, appreciated as much for ornamental appeal as for taste. Both form long-lived, fragrant clumps and are perennial.

Most popular

Crambe maritima - Sea Kale

As beautiful as it is tasty! This cabbage forms attractive clumps with edible bluish-green leaves and a delicate, airy display of fragrant white flowers. Worth adding to garden for visual pleasure, and to vegetable patch of any curious gardener.

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

See the product sheet

Our favourites

Crambe cordifolia - Greater Sea Kale

Imposing yet airy, this perennial cabbage makes a statement in ornamental gardens with large fleshy leaves topped by a fragrant white flowering at head height. Suits sunny positions in large flower borders!

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

See the product sheet

Crambe cordifolia - Flowering Sea Kale Seeds

A very elegant perennial cabbage forming a veritable cloud of small white flowers with a honeyed scent. It will add a poetic touch to planting schemes.

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

See the product sheet

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 coastal plant, sea kale appreciates mild, humid climates and tolerates salt spray well, making it a good plant for coastal gardens. It does not tolerate drought well. It prefers stony ground, even calcareous, and above all very well-drained but retaining coolness at depth. It will be perfect with vegetable garden plants, of course, but also in ornamental gardens 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 situation sheltered from strong winds that could break its tall stems, and although it tolerates poor soil, it will reach its full potential in more fertile soil.

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

Give Cloud cabbage a well-open position, because it hates crowding and root competition: make sure to 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 it lightens them with its opulent yet airy flowering.

All crambes will add an airy texture to natural gardens or romantic gardens.

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. Prefer a well-aerated planting for Crambe cordifolia; this species will also 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, so transplanting is not recommended.

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

• Dig a hole 2 to 3 times the size of the rootball
• Spade soil deeply
• Lay a 20 cm layer of gravel at the bottom of the hole
• Mix river sand half and half with the excavated soil
• Plant without burying the collar
• Backfill the planting hole
• Gently firm the soil with your hand
• Water regularly after planting and mulch

When and how should Crambe cordifolia and sea kale be sown?

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

In seed tray

• Sow Crambe seeds thinly in seed tray or in modules filled with potting compost mixed with sand
• Cover seeds with a 5–6 mm layer of potting compost
• Press down lightly
• Keep compost moist but not waterlogged at 15–18 °C until germination, which usually occurs between 3 and 5 weeks
• Pot on the sturdiest seedlings into small buckets of 7.5 cm
• Plant out when young plants reach about 10 cm (at 5–6 leaf stage) and after 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 soil well and loosen deeply
• Add leaf mould and coarse sand
• Sow in small groups of 2 to 3 seeds
• Cover with soil
• Water seedlings regularly during emergence
• Thin to at least 50 cm, more for crambes cordifolia

Succeed in sowing perennials, it’s easy by following our tips!

Striking graphic foliage of sea kale

Maintenance, pruning and care

Undemanding, Crambe is easy to grow and requires little attention.

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

The Cloud Cabbage (Crambe cordifolia) is more demanding than sea kale: each spring fork in a light dressing of compost around its base.

Cut faded flower stalks to prevent them setting seed (unless you wish to collect seeds for sowing, in which case keep a few as seed-bearers). Remove old damaged and dry foliage and cut back the clump of Cloud Cabbage after flowering.

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

Harvest, uses and storage of sea kale

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

When to harvest the sea kale

Evergreen leaves can be picked as required, throughout the year. Young shoots, on the other hand, are harvested before flowering, from February–March to April after having been previously blanched.

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, dressed with vinaigrette, in gratin or in soup. Flower buds are enjoyed raw or cooked.

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

Potential diseases and pests

Planted in well-drained soil, crambe has good longevity and good resistance to diseases. It dislikes excess water and gastropods at shoot emergence.

Protect young shoots from snails and slugs : follow our tips for controlling gastropods!

Like all cabbages, crambe foliage can be devoured by flea beetles and cabbage whites: spray a tansy leaf decoction, dislodge unwanted pests by regularly spraying foliage.

Cabbage white caterpillar

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

Multiplication

Crambe is propagated by clump division in spring or autumn on a plant aged 4 or 5 years or by sowing from March to June. Root cuttings are also possible in autumn on a plant already well established.

Clump division

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

By root cuttings

• Take 10 cm sections containing roots and buds
• Push them into buckets filled with potting compost and river sand
• Water regularly
• Protect from frost
• Plant out into open ground the following spring when cutting has developed sufficient roots

Sowing

Sowing is done in spring with fresh Crambe seeds of the year, harvested as soon as they turn yellow or with our Crambe seeds sold in easy-to-sow sachets. Germination can sometimes be slow and erratic. Proceed according to the method shown in our section “When and how to sow Crambe cordifolia and Crambe maritima?”

Companion planting crambe in the garden

With their airy flowering and fleshy bluish-green leaves, heart-shaped on cloud cabbage, Crambe bring breath, exuberance and lightness to garden, transforming simple perennial border into grand, poetic tableau. They are a staple of English cottage gardens, country gardens and seaside gardens, where they create opulent, romantic summer scenes. They also work well in white garden.

Sea kale is spectacular in vegetable garden as well as ornamental garden, although cloud cabbage’s strong personality makes even greater impression!

An idea for a combination in a palette of acid 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 pair, slotting effortlessly into natural, lush scenes. Depending on species, Crambe can play dazzling role as mid- or back-of-border plant creating luminous floral mist, or as a mossy foreground for mixed border.

Crambe is slow to establish and, once well settled, its foliage quickly fades after flowering, becoming rather untidy, so better to mask 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 help keep base cool.

In gravel bed, sea kale will make an impact year‑round, remaining through winter; pair with perennials with exotic look such as agaves, architectural grasses like carex or other evergreen perennials such as artemisias, creeping bugles or pussy ears, sedums or white delospermas, in white and silver harmonies.

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

Crambe pairs admirably with glaucous foliage of Achilleas millefolium, Euphorbias, nepeta and even lavenders.

→ More ideas for combining Crambe in our care sheet