How to grow sea kale
All you need to know about growing sea kale, in this detailed Grow Guide.
Sea kale, Crambe maritima, is a striking plant that is both ornamental and edible. The large leaves are a lovely glaucous green, with wavy edges, and in summer these are crowned with a cloud of tiny white perfumed flowers. These nectar-rich flowers are great for attracting pollinating insects. As the name suggests, sea kale is often found growing wild on the coast. In gardens, it looks good planted in dry sunny beds or into gravel, with other plants that favour this habitat, such as knifphofia and thrift. Or you could include it in your vegetable plot and harvest the young shoots in spring to eat raw or steamed – they taste like asparagus.
Where to plant sea kale
For best results, grow sea kale in full sun or partial shade in fertile, very well-drained soil. The position needs to be deep enough to accommodate the long tap root of the plant with plenty of space for it to spread out. Sea kale is not suitable for growing in containers.
How to plant sea kale
You can grow sea kale from seed. The round bullet-like seeds have a hard, outer casing, so soak seeds and score to remove this before planting the seed in compost with a little bit of heat. Alternatively, young plants can be grown from root cuttings. Plant out young sea kale plants in early spring, into a well-prepared bed that is the final position for these perennial plants as they don’t like being moved.
Propagating sea kale
You can collect seed from sea kale plants at the end of the summer or take root cuttings – also known as ‘thongs’ – from older plants. These might be established sea kale plants coming to the end of their life so they can be dug up. Take cuttings from the side roots. Plant these ‘thongs’ into compost in early spring, covering with a layer of compost 2cm deep and grow on.
Sea kale: problem solving
Sea kale is a member of the brassica family and therefore can succumb to club root. They may also be attacked by flea beetles, while slugs and caterpillars love the tender young leaves, so use netting or other barrier methods to protect them.
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Looking after sea kale plants
Seakale is a perennial and should be cut back in autumn. In spring add a thick mulch of well-rotted manure or garden compost. If you want to grow seakale as an edible, force the plants over winter, covering with a bucket or rhubarb forcer to get flavoursome young shoots that can be eaten raw or steamed. However, don’t try this until the second year, as it will weaken the plant.
Sea kale varieties to grow
Crambe maritima grows to 75cm and is a perennial with large glaucous green leaves and small, scented white flowers.
Crambe cordifolia has been given the Royal Horticultural Society’s prestigious Award of Garden Merit (AGM). Larger than its maritime cousin, it grows to 1.8m and the foliage is dark green. The frothy sprays of small, scented white flowers are followed by seed pods. It looks good in a sunny border whether you are using it for the foliage or flowers. Beware, as the leaves have a good aroma of cabbage, but are not edible.