Sea kale: A veggie made in the shade

“The greatest service which can be rendered any country is to add an useful plant to its culture.” – Thomas Jefferson, ca. 1800

In Sunday’s column, I wrote about some vegetable plants that don’t mind a bit of shade, including: bush beans, beets, carrots, leafy greens, onions, peas, perennial herbs, potatoes and radishes. In addition, some vegetables taste better when the young shoots are covered to prevent exposure to the sun, which stops photosynthesis from occurring and results in paler produce with a more delicate flavor and texture. This shading process is called blanching; vegetables that are often blanched include celery, endive, leeks, white asparagus, lovage, rhubarb and sea  kale.

Thomas Jefferson grew sea kale (Crambe maritima), a perennial member of the cabbage family, at Monticello in the early 1800s. He used clay pots to cover the shoots, but mulch, rocks, boards and plastic pots can also be used. Jefferson ate the tender shoots steamed like asparagus; young blanched leaves can also be cooked and eaten like collards or spinach, and the young flower stalks can be prepared and eaten like broccoli. One species, Crambe orientalis, has a thick root, full of nutrition, that can be used as a substitute for horseradish.

Sea kale blooms in the summertime with a profusion of pretty white flowers. For this reason, it is sometimes grown as an ornamental plant in rock gardens, and the Royal Horticultural Society in England has recognized it as a garden plant of merit. Although its native climate is along northern European coastlines, sea kale is winter hardy down to USDA Hardiness Zone 5 (the Rogue Valley is in Zone 8a/b) and tolerates heat up to AHS Heat Zone 8 (the Rogue Valley is listed as  Zone 6). Sea kale is not difficult to grow as long as it is provided with a sandy loam that drains well but stays moist throughout the hot summer months.

The key to growing sea kale is patience. It’s a long-lived plant, producing for about 12 years, but it should be left alone in the garden for two seasons before harvesting during the third season. Sea kale can be started by seed, but germination is erratic and can take up to three years. It’s easier to start sea kale from root cuttings called thongs. I ordered my thongs online from Cultivariable. They are about 4 inches long and the thickness of a pencil. Before planting, soak the thongs for a few hours and then plant them vertically in the soil, 12-15 inches apart, with the thicker cut about 2 inches below the soil surface. Add some compost to the planting hole and  organic fertilizer, such as liquid seaweed, around the plant, water thoroughly… and wait.

Allow the plant to grow and establish itself for two years. The leaves will die back when the weather turns cold; prune away old foliage, cover the roots with mulch… and wait some more.

After the second growing season, you can either lift the roots in November for early forcing indoors, or you can cover the plant right in the garden and take cuttings for propagating in the spring. To take cuttings, select side shoots that are about as thick as a pencil and cut into 3-6 inch pieces. Making a straight cut on the top and a slanting cut on the bottom will help prevent accidentally planting the thong upside down in the soil.

Harvest blanched sea kale shoots and leaves in early spring when still young. Shoots should be cut at soil level when they are about 8-10 inches long; eat soon after cutting. Stop cutting in May, remove the pots to allow the plants to grow naturally, and enjoy the flowers when they bloom in the summer!

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  • About the Author

    Rhonda Nowak

    Rhonda Nowak is a Rogue Valley gardener, writer and teacher. With more than 25 years of gardening experience and a Ph.D. in literature and language arts education, she combines a love for plants, poetry, and prose in her Literary Gardener blog. ... Full Profile
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