Sea Kale

Sow sea kale seed in pots in a cold frame

Sow seed into pots in a cold frame in spring, then grow the seedlings on before setting them into their permanent bed. Autumn sowing in a cold frame works equally well if you missed spring. Choose a site in full sun with well-drained soil and shelter from strong winds. Sea kale is a coastal shingle and sand plant, so it wants sharp drainage and sun; raising it in pots under a cold frame gets you even germination and a root system worth transplanting instead of losing small seedlings in open ground.

Lime the bed to pH 7.0-7.2 before you ever plant sea kale

The autumn before planting, test the soil and lime to pH 7.0-7.2, incorporating it thoroughly rather than leaving it on the surface. Lime reacts slowly, so getting it in months ahead of planting is the point. If you raise pH substantially, watch boron levels afterward. Sea kale is a brassica and susceptible to club root, whose resting spores persist in soil for years and germinate poorly in alkaline conditions. This is a perennial crop that sits in one bed for a decade, so you cannot rotate your way out of trouble later - pre-plant pH is the only lever you get.

⚠ Lime well ahead of planting and incorporate thoroughly; monitor boron when pH is raised. If club root is already confirmed in a bed, rotate out of brassicas for 7 years rather than planting a perennial into it.

Take root cuttings (thongs) while the plants are dormant

In winter, lift and cut 8-10 cm sections from the side roots and hold them cool and at high humidity until you plant them out. Root cuttings are the most efficient way to propagate sea kale and give you plants true to the parent. Sea kale regenerates readily from root pieces, and a cutting carries enough stored energy to throw up new sprouts on its own. Seedlings vary; a thong is a clone of a plant you already know cropped well.

⚠ Cuttings dry out fast once lifted - keep them cool and humid until planting or they will fail.

Divide established sea kale crowns in early spring

In early spring, lift a crowded old crown and split it, replanting divisions with healthy root attached. This is the simplest way to increase a planting if you did not take root cuttings over winter. Division in early spring catches the plant as it breaks dormancy, so the pieces re-root while the crown is already pushing new growth rather than sitting cut and idle.

Cut sea kale down to ground level in autumn

Once the leaves yellow and abscise in autumn, cut the whole plant down to ground level and clear the debris away from the crown. Growth stops and the foliage drops on its own as the season closes, so the top is finished doing anything useful. Clearing it removes the damp cover slugs overwinter in and leaves you a clean crown to find and cover when you force it in spring.

Check for slugs on emerging shoots after rain

Go out in the evening with a flashlight after cloudy or rainy weather and look for irregular holes and slime trails around the crowns and under nearby debris. Handpick and drown them in soapy water, or set a board out overnight and kill what gathers underneath each morning. Water in the morning so the bed dries by dusk, and clear excess leaf mulch in spring. If you bait, iron phosphate or ferric sodium EDTA pellets go on the soil near the plants in late afternoon. Slugs and caterpillars are the pests sea kale actually gets, and emerging shoots are the vulnerable stage - a mature plant shrugs off chewing but young growth can be destroyed outright. Slugs shelter in exactly the cool shaded damp a blanching pot creates.

⚠ Metaldehyde baits are highly toxic to dogs - do not use where pets have access. Iron phosphate and ferric sodium EDTA are the safer choices around children and pets. Scatter bait on the soil, never on open flowers.

Blanch the crown in total darkness as the first shoots stir

As the first spring shoots begin to move at the crown, cover the plant with a lightproof pot, bucket or traditional forcing pot to exclude light completely. Allow roughly four weeks under cover - sprouts take about 28 to 30 days to reach harvest size in the dark. Keep the cover fully lightproof; any leak defeats the purpose. Excluding light stops chlorophyll forming, so the shoots come up pale, sweet and tender instead of green and bitter. This is not a garnish step - unblanched sea kale shoots are the reason most people who try the crop once never eat it twice.

Cut the blanched shoots, then uncover and let the plant feed itself

About 28 to 30 days after covering, lift the pot and cut the pale shoots at the crown while they are still crisp and tender. Take your cut, then remove the cover for the rest of the season and let the plant leaf out fully. Cook the shoots like asparagus; the young leaves and the flowering shoots are also edible. Yield per crown runs anywhere from 30 to 120 g depending on how much root biomass the plant has built, so the foliage it makes after harvest is literally next spring's crop. Keep cutting or keep it covered and you are eating the root reserves that would have fed the following year.