Perennial
How to grow sea kale
Crambe maritima
Sea kale is a hardy perennial grown for the pale shoots it produces when forced in darkness in late winter. Plant root cuttings, called thongs, in March or April in full sun and sharply drained soil, leave them to build up for two years, then cover the crowns in January and cut the blanched shoots from March to May. Drainage and patience are what matter: a crown forced too young or cut too long is quickly exhausted.
- Hardiness
- Fully hardy, a native of shingle beaches
- Position
- Full sun
- Soil
- Free-draining, sandy / coastal
- Ideal pH
- 6.5 to 7.5
- Water
- Low
- Feeding
- Moderate feeder
Sowing and planting sea kale
WhenPlant thongs Mar to Apr; force Jan to Mar; harvest blanched shoots Mar to May from year two
Starting off
Plant thongs (15 cm root cuttings, 1 to 2 cm thick, cut square at the top and sloped at the base) in March to April, taken from an established plant in November and stored in sand until buds form. Seed is sown 2 cm deep in April, germinating in 14 to 28 days, and takes 3 years to crop. 'Lilywhite' is the classic variety.
Spacing and planting
Plant root cuttings (thongs) or crowns 45 to 60 cm apart in rows 60 cm apart, the top of the thong 2 to 3 cm below the surface; the plant grows 60 cm tall and 90 cm across. A deep 45 cm pot of gritty compost will carry one plant, and a forced crown is easy to cover.
Varieties worth growing
- Lilywhite
- The classic garden selection, with shoots that blanch to a clean ivory with no purple tinge. Sold as thongs or young plants. Also sold as Lily White.
- Angers
- A French strain usually supplied as thongs, selected for forcing and reliable shoot quality.
- Species (Crambe maritima from seed)
- Cheaper if you want several plants, and handsome in a gravel garden, but variable, slow to germinate and a year behind thongs.
Sea kale month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Cover crowns that are at least two years old with a forcing pot or upturned bucket, blocking all light.
- February
Check under the covers weekly for slugs. Keep the light out.
- March
Cut the first blanched shoots at 15 to 20 cm. Plant thongs.
- April
Keep cutting. Plant thongs and young plants. Sow seed.
- May
Stop cutting and take the covers off. Feed and mulch the crowns.
- June
Water new plants in dry spells. Remove flower stems from young plants so they build strength.
- July
Weed. Check for caterpillars.
- August
Nothing to do beyond weeding.
- September
Nothing to do.
- October
Remove yellowing leaves as they die back.
- November
Clear all dead foliage from the crowns. Lift a three-year-old plant to take thongs and store them in damp sand.
- December
Nothing to do. Get forcing pots ready.
Feeding sea kale
A light feeder adapted to shingle. One modest feed after the forcing season replaces what cutting took; more than that produces lush leaf at the expense of a sound crown.
Light-to-moderate; seaweed and grit suit its coastal nature.
Feeding plan
Before planting, only if a pH test reads below 6.5
Garden Lime (calcium carbonate)
About 0.5 kg/m² worked in during late winter, at least a month before planting. On neutral or chalky soil, none.
May, when the forcing covers come off
Fruit & Vegetable Fertiliser 4-5-6
70 g/m², the bottom of the label range. A crown at 60 cm spacing occupies about 0.36 m², so that is 25 g per plant (70 × 0.36), scattered around the crown and watered in.
May, after feeding
Garden compost
A 3 cm mulch around, not over, the crown. On heavy soil use grit or gravel instead.
Every 3 weeks, June to August, optional
1 g per litre of water as a drench or foliar spray: 5 g in a 5 litre can does four or five plants.
Signs to watch
Thin, weak forced shoots
A crown exhausted by cutting too long or too young
Cut for 6 weeks only and leave plants 2 years before forcing
Yellow, small leaves in summer on sandy ground
Nitrogen short
A light balanced or seaweed feed after cutting
Scorched brown leaf edges after a hot spell
Drought, not a shortage
Water deeply weekly
Pests, diseases and problems
Blanched shoots chewed and slimy under the forcing pot
Slugs, which gather in the dark, damp space under the cover
Clear all dead leaves from the crown before covering, lift the pot weekly to check, and remove any slugs by hand. Dry leaves or straw packed loosely inside make it less inviting than bare, wet soil.
Small round holes peppering the leaves of young plants in spring and summer
Flea beetle
Cover newly planted thongs and seedlings with fine insect mesh for their first summer and keep them watered. Established crowns outgrow the damage.
Leaves eaten ragged from July to September
Caterpillars of the large and small white butterflies
Pick off egg clusters and caterpillars weekly, or net plants with fine mesh. Losing leaf in summer weakens the following spring's shoots, so it is worth doing.
Plants stunted and wilting, roots swollen and distorted
Clubroot, which affects sea kale like any other brassica
No cure. Never plant on ground known to have clubroot, buy thongs from a clean source, and keep the bed apart from the cabbage patch.
Crown soft and black in spring, with few or no shoots
Crown rot in heavy soil that lies wet over winter
Plant on a raised bed or ridge with plenty of grit or sharp sand worked in. On clay, grow it in a deep pot instead.
Harvest and rotation
Harvest and storage
Force from the second winter by covering each crown with a 40 cm pot in January, sealed against light; cut the blanched shoots at 15 to 20 cm in March to April with a knife at the base, and stop by May. A crown gives 300 to 500 g of shoots per spring from year three and crops for 7 to 10 years. Use within 2 days.
Rotation and companions
Rotation: a perennial brassica kept 7 to 10 years, so no rotation, but site it away from the brassica beds. Grow it with asparagus and rhubarb in the permanent corner. Keep away from other brassicas and from anything that will shade it.
Good to knowForce the crowns in spring under a pot for blanched, tender shoots.
Growing sea kale in pots
Sea kale has a long taproot but grows well in a deep pot, which is the best answer on heavy clay. Use a container at least 45 cm deep, of around 40 litres, with a soil-based compost such as John Innes No. 3 mixed with a third grit. Mix in Fruit & Vegetable Fertiliser 4-5-6 at 5 g per litre at planting, which is 200 g for a 40 litre pot, and top-dress with 2 g per litre (80 g) each May after cutting. Water regularly in summer but keep the pot on feet so it drains freely in winter. Forcing is simple: stand a second pot or bucket upside down over the first in January.
Sea kale: common questions
How do you force sea kale?
In January, clear the dead leaves from a crown that is at least two years old and cover it with a forcing pot, bucket or large upturned pot with the holes blocked, so no light reaches it. Pale shoots are ready to cut at 15 to 20 cm from March. Stop cutting in May, uncover the plant and let it grow on in full light.
How long does sea kale take to grow?
From thongs, expect the first forced shoots in the second or third spring after planting. From seed it takes about three years. Once established, a crown crops every spring for seven years or more.
Can you eat sea kale without forcing it?
Yes, the young spring leaves and the unopened flower heads are edible and can be cooked like sprouting broccoli, but unblanched growth is tougher and more bitter. Take only a little from each plant, as it needs its leaves to build next year's shoots.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.
- Crambe maritima (sea kale)RHS
- Crambe maritima 'Lilywhite'RHS
- How to grow sea kaleBBC Gardeners' World Magazine