Fertilising guide
How to fertilise Sea Kale (Crambe maritima)— schedule & NPK
Also called sea kale, crambe, seakale.
More about sea kale
About Sea Kale
Crambe maritima · also called sea kale, crambe · edible
Sea kale is a hardy maritime perennial in the cabbage family, grown for its blanched young shoots that taste like a nutty cross between asparagus and cabbage. Plants form a glaucous blue-green mound and crop for years once established. Force shoots under pots in late winter, then let the plant build reserves through summer.
Growth habit: Clump-forming herbaceous perennial with a thick fleshy taproot and a rosette of large, wavy, waxy blue-grey leaves, topped by frothy white honey-scented flowers in early summer.
What fertiliser sea kale actually wants — and why
Sea Kale is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.
A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops.
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 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 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 sea kale:
Top-dress in spring with well-rotted manure or compost; sea kale relishes seaweed mulch, echoing its shoreline origins. A balanced general feed at growth onset supports the crown after forcing. Avoid high-nitrogen feeds that produce soft, rot-prone growth. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).
The dormant-season rule matters more than the exact interval: skip feeding entirely when 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 sea kale
Use the vegetable-feed label rate for sea kale. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.
Feeding always goes onto already-damp soil, never dry roots — water 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 sea kale watering schedule.
Signs you are over-feeding sea kale
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for sea kale:
- Very soft, floppy, dark-green growth that attracts aphids.
- Excess leafy growth at the expense of hearts/heads in cabbage and the like.
- Salt crust and scorched leaf edges in containers; nitrate-heavy leaves.
Signs you are under-feeding sea kale
- Pale, yellow-green leaves, oldest first, and slow growth.
- Small, tough, bitter leaves and premature bolting.
- Weak, stunted heads in cabbage, broccoli and cauliflower.
If the symptoms point at watering, light or roots rather than nutrition, the full sea kale care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
For container-grown sea kale, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.
Organic vs synthetic feeds for sea kale
Organic options
Well-rotted manure or compost dug in, plus nitrogen-rich liquid feeds like diluted chicken-manure pellets or nettle feed. UK: pelleted chicken manure or Westland; US: Espoma Garden-tone or blood meal. Steady and soil-building.
Synthetic / liquid feeds
A balanced feed at planting then a high-nitrogen liquid or granular side-dress — UK: Growmore then a nitrogen feed or Phostrogen; US: a 10-10-10 then a high-N (e.g. 21-0-0) side-dress or Miracle-Gro.
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 sea kale — frequently asked questions
What fertiliser does sea kale need?
A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops. Sea Kale is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.
How often should I feed sea kale?
Top-dress in spring with well-rotted manure or compost; sea kale relishes seaweed mulch, echoing its shoreline origins. A balanced general feed at growth onset supports the crown after forcing. Avoid high-nitrogen feeds that produce soft, rot-prone growth. Top-dress in spring with well-rotted manure or compost; sea kale relishes seaweed mulch, echoing its shoreline origins. A balanced general feed at growth onset supports the crown after forcing. Avoid high-nitrogen feeds that produce soft, rot-prone growth. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).
What strength of feed for sea kale?
Use the vegetable-feed label rate for sea kale. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.
What does over-feeding sea kale look like?
Very soft, floppy, dark-green growth that attracts aphids. Excess leafy growth at the expense of hearts/heads in cabbage and the like. Salt crust and scorched leaf edges in containers; nitrate-heavy leaves. Letting sea kale run short of nitrogen mid-crop is the main mistake — growth checks, leaves toughen and brassicas/leafy greens bolt or turn bitter. Keep nitrogen steadily available.
Should I flush the soil of sea kale?
For container-grown sea kale, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.
Keep reading
- Sea Kale care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water 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 tomato
- How to fertilise pepper
- How to fertilise cucumber
- All 5561 fertilising guides in the Growli library