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Plant care

Greater Sea Kale (Flowering sea kale) care

Crambe cordifolia

Also called Greater sea kale, Flowering sea kale, Colewort, Giant sea kale.

RHS H5USDA 5-9Mildly toxic to petsIndoor 1.5–2.5 m tall in flower by 1–1.5 m wide (5–8 ft × 3–5 ft)

Watering rhythm

Bright indirect light (just back from a sunny window)

Moderate — water regularly while establishing, then during dry spells

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Light

Bright indirect light (just back from a sunny window)

Soil

Deep, fertile, moist but well-drained chalk, loam, or sandy soil; neutral to slightly alkaline pH preferred

Humidity

Moderate

Temp

-20°C to 28°C

Pet safety

Mildly toxic to pets

Mature size

1.5–2.5 m tall in flower by 1–1.5 m wide (5–8 ft × 3–5 ft)

Care at a glance

Light

In the wild greater sea kale grows on the bright edge of a forest canopy, not in the canopy and not in the open. Indoors, that translates to within a metre of an unobstructed window, sheer curtain optional. Performs best in full sun but tolerates light dappled shade; in partial shade, flowering is still generous though stems may be slightly less robust. The fastest test: a hand held at the leaf casts a soft-edged shadow at noon — sharp shadow means too much sun, no shadow means too little light.

Watering

Aim for moderate — water regularly while establishing, then during dry spells for greater sea kale, but treat that as a starting point rather than a rule. A south-facing summer windowsill will dry the pot twice as fast as a north-facing winter room. Lift the pot; if it feels noticeably lighter than it did wet, water it. Keep soil evenly moist during the first growing season; once established it tolerates short dry spells, but extended drought during the flowering period reduces bloom quality.

Soil and pot

Greater Sea Kale grows best in deep, fertile, moist but well-drained chalk, loam, or sandy soil; neutral to slightly alkaline ph preferred. A deep, stone-free soil suits the substantial taproot; dig in well-rotted compost at planting. Acid soils should be limed to neutral before planting. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Greater Sea Kale sits happiest at around Moderate humidity and -20°C to 28°C (-4°F to 82°F). Tolerates average UK outdoor humidity comfortably; sheltering from strong winds is more important than humidity management, as wind shreds the large leaves and can topple the tall flowering stems. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed greater sea kale sparingly. Apply a balanced granular fertiliser in spring as new growth emerges; a second light feed in early summer supports the energy demands of the large flowering canopy. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on greater sea kale in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Cabbage white butterfly caterpillars — As a member of the Brassicaceae, plants can be attacked by the caterpillars of large white and small white butterflies, which can reduce the large foliage to a skeleton. Check the undersides of leaves in summer and remove eggs and caterpillars by hand.
  • Club root (Plasmodiophora brassicae) — This soil-borne pathogen, common in brassica beds, can infect Crambe and cause distorted, swollen roots and poor growth. Raise soil pH above 7.0 with lime, improve drainage, and avoid planting in ground with a history of club root.

Propagation

Root cuttings (3–10 cm sections planted just below the surface in spring) are the most reliable method. Can also be raised from seed sown in a cold frame in March–April, though germination is slow (3–26 weeks at 15°C). Division of established clumps in spring or autumn is possible but difficult due to the fleshy taproot. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Greater Sea Kale is mildly toxic to pets. No known hazards or toxic principles are documented for Crambe cordifolia; the plant is in the edible Brassicaceae family and young leaves are consumed by humans. However, Crambe is not listed on the ASPCA Toxic and Non-Toxic Plant database, so an explicit pet-safe classification cannot be confirmed. Err on the side of caution and prevent pets from ingesting large quantities. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Greater Sea Kale care — frequently asked questions

What is the common name for Crambe cordifolia?

Crambe cordifolia is most commonly called Greater Sea Kale, but it is also known as Greater sea kale, Flowering sea kale, Colewort, Giant sea kale. The names refer to the same species, so care instructions for Greater Sea Kale apply identically to anything sold as Flowering sea kale.

How much light does greater sea kale need?

Greater Sea Kale grows best in bright indirect light (just back from a sunny window). Performs best in full sun but tolerates light dappled shade; in partial shade, flowering is still generous though stems may be slightly less robust.

How often should I water greater sea kale?

Water greater sea kale moderate — water regularly while establishing, then during dry spells. Keep soil evenly moist during the first growing season; once established it tolerates short dry spells, but extended drought during the flowering period reduces bloom quality. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is greater sea kale toxic to cats and dogs?

Greater Sea Kale is mildly toxic to pets. No known hazards or toxic principles are documented for Crambe cordifolia; the plant is in the edible Brassicaceae family and young leaves are consumed by humans. However, Crambe is not listed on the ASPCA Toxic and Non-Toxic Plant database, so an explicit pet-safe classification cannot be confirmed. Err on the side of caution and prevent pets from ingesting large quantities.

What USDA hardiness zone does greater sea kale grow in?

Greater Sea Kale is rated for USDA zone 5-9 and RHS hardiness H5. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Greater Sea Kale deep-dive guides

Every aspect of greater sea kale care, each with its own calibrated guide:

Featured in these plant shortlists

Greater Sea Kale qualifies for 4 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Greater Sea Kale is also known as Greater sea kale, Flowering sea kale, Colewort, and Giant sea kale.