Greater sea kale

Greater sea kale: how do you recognise it?

Habit

Large, broad clump: a low mound of leaves with flowering stems up to 1.8 m; 1.5 m across.

Leaves

Large, heart-shaped, coarse and rough, dark green, with a wavy, toothed edge.

Flower

Countless small white four-petalled flowers in a loose, much-branched panicle, in June and July.

Scent

A sweet honey scent that is easy to notice on warm days.

Roots

A deep, fleshy taproot.

Flowering: June–July · Plants: March–April and September–October · Pruning: July–August and November

Why grow it?

• A spectacular focal point: a cloud of white flowers almost 2 m tall.
• The flowers smell of honey and attract plenty of bees and other insects.
• Thanks to its airy flower heads you can see through it: lovely in a large border or against a dark hedge.
• Hardy and, once established, well able to cope with drought thanks to its deep taproot.
• Long-lived if left undisturbed.

Greater sea kale: where does it grow best?

• Full sun for the most flowers.
• Deep, free-draining soil: sand, loam or clay, neutral to chalky.
• Dry to moist; no wet feet in winter.
• Allow 1.5 m of space: the large leaves shade smaller neighbours.
• Sheltered from strong wind, or the heavy flower head may blow over.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Neutral or chalky

Moisture

Dry or normal

Size

1.8 m tall, 1.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Delphinium: Blue spikes in front of the white cloud, in the same month.
• Roses: A romantic pairing in a sunny border.
• Catmint: A low blue edging in front that later hides the dying leaves.
• Ornamental grasses: They fill the space the sea kale leaves free in late summer.
• Michaelmas daisy: Flowers later and takes over after the crambe has finished.

Greater sea kale: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October, when the soil is neither frozen nor waterlogged.
2. Dig a deep hole and loosen the subsoil so the taproot can go down deep.
3. Mix in some compost; on heavy clay add coarse sand too.
4. Set the plant at the same depth as in its pot and keep 1.5 m clear around it.
5. Water well straight away and again in dry spells during the first season.
6. Protect the young leaves from slugs.

Care

Water

In dry spells in the first year; after that only in very dry summers.

Feeding

A layer of compost or well-rotted manure in spring.

Support

Usually not needed; in a windy spot, put a few sturdy stakes around the flowering stem.

After flowering

Cut off the flowering stem once the flowers have faded and remove tatty leaves.

Leave alone

Leave it undisturbed: moving it often fails because of the long taproot.

Tip: Plant it straight away in its permanent spot and put late flowers such as ornamental grasses or asters in front: they fill the gap when the leaves die back after flowering.

Greater sea kale: when to prune it?

Pruning months: July–August and November.

When: After flowering, in July–August, cut off the flowering stems; in November clear away the dead leaves.

How:

• Cut the faded flowering stem off at the base.
• The leaves often partly die back after flowering: remove yellowed and nibbled leaves.
• In November clear away the dead leaves, so slugs have fewer hiding places.

Caution: After flowering there is often a gap in the border: put late-flowering plants in front of or beside it.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Root cuttings

From December to February: carefully dig up a piece of root at the edge, cut it into 5–8 cm lengths and push them upright into pots of sandy cutting compost. They sprout in spring; plant them in their final spot in autumn.

Division

Not recommended: the taproot divides poorly and the plant struggles to recover.

Greater sea kale: how does it get through the winter?

Hardy to −30 °C.

• Hardy to about −30 °C: no protection is needed in Belgium.
• The top growth dies back; it reshoots from the taproot in spring.
• Wet soil in winter can make the root rot: make sure drainage is good.

Diseases and pests

• Slugs: They make large holes in the young leaves in spring. Pick them off in the evening and clear away hiding places.
• Cabbage white caterpillars: Green caterpillars on the leaves in summer. Pick them off; blue tits and great tits help too.
• Flea beetles: Small holes in young leaves in dry weather. Water; the plant usually grows away from the damage.
• Blowing over: The large flower head falls over in a storm. Choose a sheltered spot or give support.
• Few flowers: Young plants often flower only sparsely in their first years. Be patient: full flowering comes after a few years.

Through the year

• January: Take root cuttings.
• March: Add compost. Plant.
• April: Plant. Watch for slugs on the young leaves.
• May: The flowering stem grows. Stake it in a windy spot.
• June: Flowering: a white, honey-scented cloud full of bees.
• July: End of flowering. Cut off faded stems.
• August: Clear dead leaves. Water in severe drought.
• September: Plant.
• October: Plant.
• November: Clear away dead leaves.
• December: Take root cuttings.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• It is related to cabbage and to sea kale (Crambe maritima), which grows wild on beaches along the Atlantic and the North Sea.
• The name cordifolia means ‘with heart-shaped leaves’.
• Each tiny flower has four petals in a cross, typical of the cabbage family, which also includes mustard.