Fertilising guide
How to fertilise Greater Sea Kale (Crambe cordifolia)— schedule & NPK
Also called Greater sea kale, Flowering sea kale, Colewort, Giant sea kale.
More about greater sea kale
About Greater Sea Kale
Crambe cordifolia · also called Greater sea kale, Flowering sea kale · flowering
Crambe cordifolia is a majestic herbaceous perennial native to the Caucasus region and northern Iran, producing enormous dark green, heart-shaped, lobed basal leaves and a spectacular cloud of tiny, fragrant white flowers on branched stems up to 2 m tall in early summer. It thrives in deep, fertile, well-drained neutral to alkaline soil in full sun or partial shade, forming a bold architectural focal point in borders. Young leaves and roots are edible with a cabbage-like flavour, though the plant is primarily grown as an ornamental. No toxicity has been documented for this species in veterinary literature; it is an edible Brassicaceae member, but treat as mildly toxic out of caution as it is not on the ASPCA confirmed non-toxic list.
Growth habit: Bold, clump-forming herbaceous perennial with huge basal leaves dying back in autumn and tall, airy, repeatedly branched flower stems in early summer.
What fertiliser greater sea kale actually wants — and why
Greater Sea Kale is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for greater sea kale: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed greater sea kale, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For greater sea kale:
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. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when greater sea kale is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for greater sea kale
Half strength is the safe default for greater sea kale — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water greater sea kale first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the greater sea kale watering schedule.
Signs you are over-feeding greater sea kale
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for greater sea kale:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding greater sea kale
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full greater sea kale care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of greater sea kale with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for greater sea kale
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising greater sea kale — frequently asked questions
What fertiliser does greater sea kale need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Greater Sea Kale is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed greater sea kale?
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. 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. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for greater sea kale?
Half strength is the safe default for greater sea kale — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding greater sea kale look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding greater sea kale year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of greater sea kale?
Flush the pot of greater sea kale with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Greater Sea Kale care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water greater sea kale — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise iris
- How to fertilise crocus
- How to fertilise hyacinth
- All 10153 fertilising guides in the Growli library