How to Grow Crambe Plants in your Garden

Gardener's HQ Guide to Growing Sea Kale, Colewort, Crambe, and Giant Kale

Crambe are very large plants that can reach over two metres in height.

They are generally hardy perennials, but can also come as hardy annuals or hardy bulbs.

They are very woody in nature and bloom with white flowers in the summer.

Common names for Crambe include Colewort and Seakale.

Crambe maritima
Crambe maritima - Sea kale by Dag Endresen; Creative commons.

Crambe maritima flower
Crambe maritima flower by Phill Sellens.

Crambe Growing and Care Guide

Common Names: Sea Kale, Crambe, Colewort, Giant Kale.
Life Cycle: Hardy annual. Hardy biennial. Hardy perennial.
Height: 32 to 60 inches (80 to 150 cm).
Native: Europe, Central and Southwestern Asia, Eastern Africa.
Growing Region: Zones 5 to 9.
Flowers: Late spring and summer.
Flower Details: Yellow, cream, white. Florets. Honey fragrance.
Foliage: Cabbage-like.
Sow Outside: 1/2 inch (12mm). Biennials in late summer. Perennials before last frost or autumn. Annuals following last frost. Spacing 30 inches (75 cm).
Sow Inside: Peat pots. Germination time: three weeks to six months. Temperature 60°F (10°C). Start ten weeks in advance. Transplant perennials outdoors following the last frost or in autumn; transplant annuals following last frost; transplant biennials in the autumn.
Requirements: Full sunlight or light shade. Good drainage. Soil pH 7 to 8.5. Rich soil. Gravelly soil. Will not flower until the third year. Stake the inflorescence stem. Propagate by dividing the root balls in spring.

How to Grow Colewort and other Crambe Species

It is best to sow Crambe seeds outside in their final location at a spacing of 60 cm to a metre apart. The seeds and bulbs should be sown at a depth of about 1cm into a partially shaded or sunny area of the garden that has good drainage. They prefer a fertile soil with an alkaline pH. The timing of sowing of Crambe varies depending upon the nature of the plant. Annuals should be planted before the last frost of spring; perennials before it (early spring) and bulbs at the end of summer.

If you first plan to grow Colewort and other Crambe species indoors from seed then they should be sown in peat pots about 10 weeks before they are due to be transplanted after the last frost of spring (annuals/perennials) or the autumn (bulbs/perennials). However given the variation of germination time (three weeks to six months) it is usually best to sow the seeds outdoors.

Caring for Crambe in the Garden

It will take at least three years until you see flowers from your perennial Crambe plants. Plants should be cut back to the ground in the autumn, and regularly treated with insecticide. If you require more plants then cuttings can be taken from the root in the spring.