Ornamental kale, scientifically known as Brassica oleracea, is a striking cool-season plant cultivated purely for its aesthetic qualities, not for consumption. It is a favorite for fall and winter landscaping, providing a burst of non-fading color when most other plants have declined. The plant forms a dense, low-growing rosette of leaves that can be highly ruffled or frilly. The inner foliage displays vibrant shades of white, pink, purple, or deep red. This member of the cabbage family is prized for its ability to maintain its dramatic appearance even after enduring hard frosts.
The True Lifespan: Annual, Biennial, or Perennial?
Ornamental kale is botanically classified as a biennial, meaning its complete life cycle naturally spans two years. In its first year, the plant dedicates its energy to vegetative growth, forming the large, colorful rosette of leaves that gardeners value for display. The plant requires a period of cold temperatures, or vernalization, to trigger the next stage of its life cycle. In horticultural practice, however, it is overwhelmingly treated as a cold-hardy annual and discarded after the first season’s display. If the plant successfully survives a winter, it will “bolt” in the spring of its second year, sending up a tall flower stalk, which signals the loss of its ornamental value.
Essential Care for Vibrant Color
Achieving the deepest, most saturated colors in ornamental kale requires specific environmental conditions, primarily related to temperature. The plant needs full sun exposure to thrive, though it can tolerate partial shade, which may result in slightly less intense color development. Coloration does not fully begin until the plant is exposed to cool nights, ideally when temperatures consistently drop below 60°F (15°C). The vibrant pigments, such as anthocyanins, are concentrated in the leaves as a natural response to the chilling stress of the cold weather. Planting ornamental kale in rich, well-draining soil is important, but avoid over-fertilizing, as excessive nitrogen encourages green leaf growth at the expense of the colorful center.
The Process of Overwintering
Attempting to overwinter ornamental kale means treating it as a true biennial. The plant is impressively cold-tolerant and can generally withstand temperatures down to approximately 5°F (-15°C) once it is fully established. To maximize survival in regions with harsh winters, a heavy layer of organic mulch, such as straw or shredded leaves, should be applied around the base. This mulch acts as an insulator, protecting the crown and root system from extreme temperature fluctuations and damaging freeze-thaw cycles. Container-grown kale can be moved to a protected location, such as an unheated garage or cold frame, to shield the roots from deep freezes. If successful, the plant will emerge in the spring of the second year and begin to bolt, signaling the end of its decorative phase.
Distinguishing Ornamental from Edible Kale
Ornamental kale and the edible varieties found in grocery stores belong to the same species, Brassica oleracea, but they have been selectively bred for different traits. Ornamental varieties were cultivated to exaggerate the non-green color pigments and produce showy, tightly packed rosettes. In contrast, culinary kale is bred for texture and a less bitter flavor profile. While all kale is technically edible, the ornamental types possess a tough, waxy leaf texture and a distinctly bitter taste that makes them unpalatable for most culinary uses. Furthermore, commercially grown ornamental plants may have been treated with pesticides or fertilizers that are not certified as food-safe, so it is advised to use ornamental kale strictly for decoration.