Sea kale (Crambe maritima)
Sea kale (Crambe maritima) is a robust, ornamental and edible perennial known for blue-green foliage and fragrant white blooms. Hardy zones 5-9.
Complete Plant Information
Overview
Crambe maritima, commonly known as sea kale, is a unique, highly versatile herbaceous perennial valued for both its striking perennial foliage and its use as a traditional spring vegetable. This species commands attention in the garden with its robust, spreading habit and distinctive, large, fleshy, blue-green basal leaves that resemble collards. Beyond its aesthetic appeal, Crambe maritima offers a unique culinary harvest, with edible shoots, young leaves, flowers, and roots available throughout the season.
Native to European coastlines, this member of the mustard family readily adapts to cultivated settings, provided its basic soil needs are met. Both ornamental gardeners and food production enthusiasts appreciate sea kale for its resilience once established. It provides structure in the border while offering a rare, specialized crop that captures attention in vegetable patches across the garden.
Fast Facts
- Plant Family: Brassicaceae
- Plant Type: Herbaceous perennial
- Native Range: Europe, northern Africa, southwestern Asia
- Hardiness Zones: USDA Zones 5-9
- Size at Maturity:
- Height: 2.5-3 ft
- Spread: 2-2.5 ft
- Bloom Time: June to August
- Bloom Description: White
- Sun Exposure: Full sun
- Water Needs: Medium
- Maintenance Level: Medium
How to Grow
The ideal location for establishing Crambe maritima involves rich, well-drained loam, preferably sandy or gravelly in texture. Aim for full sun exposure, although sea kale tolerates light shade well enough to maintain its structure. It is crucial to ensure the soil pH is neutral to slightly alkaline; amend the soil with lime as needed to maintain this preference, reflecting its seaside origins. Propagation is straightforward, primarily achieved through sowing seeds or utilizing root cuttings.
Watering routines should be medium throughout the growing season, but established plants show good drought tolerance—a useful trait inherited from their maritime habitat. As this plant is grown partially as a vegetable, heavy fertilization is usually unnecessary, but ensuring rich soil at planting time is beneficial. Pruning is minimal; the primary seasonal task involves harvesting the shoots in spring or managing the robust foliage display.
For the spring vegetable harvest, delay cutting until the shoots reach about 8 inches tall and blanch them before steaming. Young leaves can be enjoyed raw or cooked similarly to spinach, while flower buds offer a broccoli-like addition to the kitchen. Do not significantly harvest foliage after the summer heat sets in to allow the plant to gather energy for winter dormancy.
Landscape Uses
Sea kale excels in mixed garden settings where its strong architectural foliage can anchor other plantings. It is an excellent candidate for dedicated vegetable gardens due to its dual-purpose nature, offering beauty and bounty simultaneously. Visually, Crambe maritima provides excellent texture contrast in borders, especially when placed near fine-leaved perennials or grasses, complementing its large, glaucous leaves.
The plant’s tolerance for dry sunny areas makes it perfect for challenging, well-drained borders or coastal-style plantings (though it does not need direct sea spray). It performs admirably in cottage gardens, where its height and unique texture fit seamlessly among traditional plantings. Furthermore, its robust nature means it responds well to container culture, provided the vessel offers superior drainage to prevent water retention around the roots.
Standout Features
Flower Qualities
- Showy
- Fragrant
Noteworthy Characteristics
Crambe maritima, commonly known as sea kale, is a robust mustard family perennial that typically grows in a spreading basal mound to 30-36” tall and to 24-30” wide. It is grown for ornamental purposes (attractive blue-green foliage and white flowers) and/or as a vegetable (edible leaves, stems, flowers and roots). Leaves are the main ornamental attraction, followed by a profuse bloom of small, fragrant, white flowers in summer.
Tolerances
- Drought
Potential Problems
Crambe maritima generally remains free of serious insect or disease problems, which contributes to its low maintenance profile. However, gardeners should monitor for common brassica pests, specifically slugs when the young shoots emerge, and cabbage moth caterpillars feeding on the leaves during warmer months. Vigilance in early spring and applying natural slug deterrents can usually manage these minor threats effectively without resorting to heavy pesticides.
Frequently Asked Questions
What hardiness zones is Sea kale suitable for?
Crambe maritima is suitable for USDA Hardiness Zones 5 through 9, providing reliable perennial performance across these ranges.
How large does Sea kale grow?
This perennial typically reaches a mature height between 2.5 and 3 feet tall, with a spread ranging from 2 to 2.5 feet wide, forming a substantial basal mound.
When does Crambe maritima bloom?
Sea kale produces its mass of small, white flowers between June and August.
What sun exposure does Crambe maritima need?
Crambe maritima prefers full sun for the best growth, although it can tolerate some light shade in hot climates.
Conclusion
Crambe maritima remains an invaluable addition to gardens, offering both superb architectural foliage and historical culinary value as sea kale. Its adaptability to dry conditions and low pest pressure make growing this robust perennial highly rewarding. Before planting, confirm your site offers the necessary sun exposure and ensure the soil is well-drained to guarantee many successful seasons of growth.
Propagation Tips
Propagation of sea kale is most reliably achieved either by sowing fresh seeds or utilizing root cuttings from established plants. When propagating by seed, remember that stratification may be beneficial to improve germination rates, mimicking the natural conditions for Crambe maritima. For root cuttings, take sections of roots in late winter or early spring, ensuring each segment has an active bud point, then plant them directly into a prepared nursery bed or pots filled with sandy, well-draining soil.
Companion Planting
Because Crambe maritima thrives in full sun and appreciates neutral to alkaline, well-drained soils, selecting companions requires attention to similar soil pH and moisture preferences. Pair it with herbs that enjoy sunny, drier spots, such as Lavender (Lavandula) or Rosemary (Salvia rosmarinus), as they share similar cultural restrictions and provide contrasting textures. In the vegetable garden, interplanting with onions or garlic can sometimes help deter underground pests near the base of the larger sea kale plants.
