Sea kale: growing & caring for Crambe maritima

Sea kale is an almost forgotten crop, but it is still considered a real delicacy in many countries. Here is our guide to this unusual perennial kale with tips on how to grow sea kale in your garden.

The wild-growing sea kale (Crambe maritima) thrives in very salty soils on the coast and used to be popular for feeding cattle. As sea kale is easy to grow and care for and is also ready to harvest early in the year, it has over time become a popular garden plant. This article will teach you everything you need to know about the origins of the plant, growing it and care.

Sea kale: origin and characteristics

Sea kale grows wild along the coasts of the Baltic and North Seas, at the Atlantic coast of Western Europe as well as the Black Sea. It used to be a very popular food for people and fodder for cattle. The plant was also known as scurvy grass because it was often pickled and taken on long sea voyages to help prevent scurvy. Nowadays, the wild-growing sea kale is protected under the Wildlife & Countryside Act (1981) and must not be picked without permission from the landowner. Although sea kale is in the cruciferous family (Brassicaceae), it is only distantly related to well-known brassicas such as kale (Brassica oleracea), broccoli (Brassica oleracea var. italica) or palm kale (Brassica oleracea var. palmifolia).

Sea kale is a winter-hardy and partly evergreen perennial with a deep tap root. In the winter, leaves and shoots usually die back but sprout again the following spring. The plant develops wavy, glaucous green leaves in the form of a rosette. The densely branched plant grows to a height of about 20 to 70 centimetres, although such large plants are rare. The flowering period lasts from May to July, when the plant produces thousands of white flowers on long flowerheads.

After fertilisation, little round pods appear, each containing a single sea kale seed. These seeds float on the water surface and spread through the tides and currents of the nearby sea. Sea kale Is extremely tolerant of salt water, making it what is known as a halophyte (salt plant). The spring shoots are considered a delicacy and can be bleached (made to turn from green to white) by covering the plant with a clay pot. Later, they can be prepared like asparagus.

Species and varieties

The genus sea kale (Crambe) is made up of about 37 different species, ten of which are native to Europe. For cooking, only Crambe maritima is used in Europe and Crambe hispanica is used in Africa. The few existing varieties of sea kale are thanks to the sporadic plantings of the vegetable in France, Holland, North America, and England. The varieties are divided into ‘Lily White’, ‘Ordinary Pink-Tipped’ and ‘Ivory White’, which mainly differ in their foliage colour and their ornamental value.

Growing sea kale

Sea kale can be grown from seed or cuttings. However, because the plants are perennial, there is no need to sow or plant sea kale again every year.

Sow your sea kale in March, either on a bright windowsill or directly in the soil in locations that are warm and protected from frost. If you let the seeds soak in water for a day before placing them about 2 cm deep in soil, they will germinate more reliably and faster. Unfortunately, the seeds have very short shelf life; after just one year, the germination rate decreases significantly. So sow any self-saved seeds as soon as possible. After a few weeks, plant out the seedlings, spacing them about 30 cm apart.

It is easier to propagate by taking root or stem cuttings from existing plants. In a nutrient-poor growing medium, such as our Plantura Herb & Seedling Compost, the cuttings will begin to root within a few days. When planting out, the sea kale needs a sunny location in loamy, sandy, well-drained soil with plenty of nutrients. Seedlings or seeds can be found in many specialist retailers these days, especially online.

The most important care measures

Straight after planting, be sure to water your sea kale a few times to encourage root growth. It will never grow as abundantly as on salty beach shores, but it can reach decent sizes as a garden plant too. After the first year of growth, the roots should be well enough established to supply the plant with water. Only during extreme periods of drought, will your sea kale need some extra watering. The nutrient requirements are moderate to high, especially if shoots or leaves are repeatedly harvested. Apply a plant-based, slow-release fertiliser, such as our Plantura Tomato Food, to replenish the soil nutrients in a balanced and sustainable way. You can also apply this when planting your sea kale.

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Harvesting sea kale

The first shoots and leaves of sea kale can be harvested as early as April. To do this, simply cut them off with a sharp knife. In summer, the leaves will have developed their distinct kale flavour and are perfect for hearty stews and soups.

Eating and preparing sea kale

Sea kale can be bleached to form white shoots by covering it with a clay pot, which is then prepared like white asparagus. Green, tender, young shoots can also be added to the menu in April and May. Sea kale leaves can be cooked and used like ordinary kale leaves.