Sea kale
Crambe maritima · Brassicaceae
Thick, waxy, blue-grey leaves with ruffled edges, like a sculpture in lead, and domes of white, honey-scented flowers in early summer.
- Size
- 24 in tall, 2½ ft wide
- Zones
- 5 to 9
- Light
- Full sun
- Flowers
- Late May to late June
- Pets
- Not checked
- Job in a bed
- Specimen
A bed built around sea kale
The planner designed this bed around sea kale when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why sea kale stands where it does.
The plants
- 1 Sea kale × 1, white
- 2 Winter heath × 11, pink
- 3 Blanket flower 'Arizona Sun' × 4, red
- 4 Foxglove beardtongue × 3, white
- 5 Switchgrass 'Shenandoah' × 3, green leaves
- 6 Eastern bee balm × 3, pink
- 7 Ornamental onion 'Purple Sensation' × 4, purple
- 8 Tulip × 3, yellow
Why this plant
- The only bold leaves here. The rest are fine and medium. A change of leaf keeps plants distinct when nothing is in flower.
- The only dense clusters. The others are bells, daisies, spires and others. Shape reads at a distance, where colours blur.
Why here
- In the middle. At 24 in it is the step between blanket flower 'Arizona Sun' (12 in) in front and switchgrass 'Shenandoah' (4 ft) behind: each is seen over the one before.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
- Bold leaf against fine. Switchgrass 'Shenandoah' is beside it: the strongest contrast of leaf there is.
Why now
- In flower for five weeks. From late May to late June.
- Part of the bed's peak. With foxglove beardtongue, eastern bee balm and ornamental onion 'Purple Sensation' in late May: 4 kinds at once. No week has more.
Planned as an English border: 5 of the 6 groups (83%) are drifts, longer along the bed than they are deep. Winter heath is the first into flower, in late January, and blanket flower 'Arizona Sun' the last to finish, in early October. The back corners are held by foxglove beardtongue and switchgrass 'Shenandoah', the tallest plants on the plan.
The planner's own design check: 11 Excellent, 6 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where sea kale goes in a border
At 24 in it belongs in the middle of a bed. In the planner's ten height classes it is medium short (18 to 24 in).
Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.
A native of British shingle beaches, and one of the finest foliage plants for dry gravel. Beth Chatto made it a signature of her gravel garden. The young shoots are edible.
- Bold blue foliage for gravel gardens
- Seaside planting
- Edible landscaping
What to plant with sea kale
Plants recorded as good partners for it, and what each pairing does:
- Sea holly: takes over when it finishes, flowering from early July; medium leaves against its bold ones; happy in the same dry soil.
- Red valerian: in flower together for five weeks, from late May; medium leaves against its bold ones; happy in the same dry soil.
- Blue oat grass: in flower together for four weeks, from early June; fine leaves against its bold ones; happy in the same dry soil.
Questions about sea kale
Does sea kale need sun or shade?
Sea kale grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled.
What zones does sea kale grow in?
USDA zones 5 to 9. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does sea kale flower in my zone?
In zone 5 it flowers late May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 5 | Late May to late June |
|---|---|
| Zone 6 | Late May to late June |
| Zone 7 | Mid May to late June |
| Zone 8 | Early May to late June |
| Zone 9 | Early May to mid June |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should sea kale be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 2½ ft (75 cm), so a group knits into one patch.
It grows 24 in (60 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many sea kale plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one, with clear ground around it: a feature plant is seen as an object, and a group of them is a thicket.
In the bed above, the planner used one in one group.
What flowers after sea kale?
Sea kale is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Sea holly: from early July to mid August, 3 ft tall (a recorded partner).
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Butterfly weed: from late June to early August, 24 in tall.
What does sea kale look like in winter?
Sea kale dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
More Crambe
- Greater sea kale Crambe cordifolia
In these guides
Every fact on record
- Type
- Perennial
- Size
- 24 in (60 cm) tall, 2½ ft (75 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Medium short (18 to 24 in)
- Place in the bed
- Middle
- Flowers
- Late May to late June; dense clusters; white
- Leaves
- Bold texture, herbaceous; blue-green, silver
- Shape
- Mounding, clumping
- Hardy in
- USDA zones 5 to 9
- Light
- Full sun
- Soil
- Lean, dry and sharply drained
- Water
- Low
- Feeding
- None needed
- Family
- Brassicaceae
Not yet checked against an outside reference: its figures rest on general horticultural knowledge. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.