How to Grow Giant Sea Kale
Crambe cordifolia
Giant Sea Kale is a jaw-dropping architectural perennial for a permanent sunny spot in well-drained soil. Its enormous dark blue-green heart-shaped basal leaves (up to 60 cm) emerge in spring, followed in June–July by towering stems bearing a billowing cloud of tiny white honey-scented flowers beloved by bees and butterflies. Plant in full sun with 120 cm of space around it — this is a statement plant that needs room. It thrives on neglect once established. Cut flower stems to the base after blooming; leave the basal leaves to die back naturally in autumn.
Yearly Lifecycle
Care Essentials
Apply a balanced general-purpose fertiliser or a generous mulch of garden compost around the crown in early spring as new growth emerges. Avoid high-nitrogen feeds — they produce lush leaves but fewer flowers.
Watch For
- Slugs and snails on emerging young foliage in spring
- Cabbage white butterfly caterpillars (Crambe is a brassica family member)
- Clubroot on waterlogged or acidic soils
- Powdery mildew on foliage in hot dry summers
Companions
Geranium (Hardy Cranesbill), Stipa gigantea, Allium hollandicum, Iris sibirica, Salvia nemorosa
Care Requirements
Light
Full sun — essential.
Giant Sea Kale demands at least 6 hours of direct sun daily. In part shade it produces lush leaves but the flower stems are weak and flopping, and flowering is greatly reduced. A south- or west-facing open border is ideal.
Watering
Low — drought-tolerant once established.
Water regularly in the first season to help the taproot establish. Once settled (typically after the second year) the plant is highly drought-tolerant and rarely needs supplemental watering in the UK. Avoid waterlogging — it will rot the taproot.
Fertilizing
Light annual feed in spring.
A single application of balanced granular fertiliser or a mulch of garden compost in early spring is sufficient. Do not feed after flowering — it is unnecessary and can encourage soft growth susceptible to disease.
Pruning
Cut flower stems after blooming; leave basal leaves.
Remove spent flower stems to the base in July–August once the blooms fade. Do not cut the large basal leaves — they fuel next year's flowering. Tidy up tatty or frost-damaged basal leaves in late winter, just before new growth appears.
Spacing
120 cm minimum between plants.
The basal rosette can reach 150 cm across at maturity. Cramped plants produce fewer flowers and are more prone to mildew. Once planted, the deep taproot makes moving the plant very difficult, so get the spacing right from the start.
Support
Not needed in a sheltered spot; may need a stake on exposed sites.
In sheltered borders the stiff branching stems are self-supporting. On exposed or windy sites, place a single tall stake centrally before the flower stems emerge to prevent wind damage to the flowering display.
Growing Tips
Choose the position once — forever
The deep fleshy taproot makes Giant Sea Kale virtually impossible to move once established. Spend time choosing a permanent sunny, well-drained spot before planting. You will not get a second chance without losing the plant.
The cloud effect needs space
The billowing flower cloud — up to 200 cm tall and 150 cm wide — only looks spectacular when the plant has breathing room. Crowded specimens produce a fraction of the flowers and are far less dramatic. Stick to the 120 cm minimum spacing.
Excellent cut flower (with caveats)
The delicate white flower sprays make beautiful, long-lasting cut flowers. Cut stems early in the morning when flowers are about two-thirds open, and condition in deep cool water. Note that the cut stems produce a slight brassica smell indoors.
Leave the basal leaves alone
After the flowers fade, resist the urge to cut back the enormous leaves. They look tatty by late summer but they are the engine that fuels next year's flowering cloud. Only remove them in late winter when new growth is about to emerge.
Spacing & Planting
| Plant spacing | 120 cm |
| Row spacing | 150 cm |
| Mature height | 200 cm |
| Mature spread | 150 cm |
Space at least 120 cm apart — plants form enormous basal rosettes up to 150 cm across and resent being crowded. Position carefully as the deep taproot makes relocation very difficult once established.
