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Garden Talk

kohlrabi plants growing in front of a wooden tobacco barn

Botanical name: Brassica oleracea
Common name: Cabbage, kale, collards
Family name: Brassicaceae (Mustard Family)
Native range: Southern and western Europe
Location in Duke Gardens: Charlotte Brody Discovery Garden, Historic Gardens
USDA Hardiness Zones: 2-11

By Katherine Hale

Marketing & Communications Assistant

Late winter and early spring is the peak season for brassicas, or members of the mustard family, in the Charlotte Brody Discovery Garden. These plants were originally sown in late summer and grown through the fall and winter, the initially bitter leaves growing sweeter over time, thanks to frosts and cold snaps. Visitors will find multiple species of Brassica represented in this year’s vegetable garden, but Brassica oleracea is by far the most abundant. This may not be obvious at first glance, due to its incredible plasticity and diversity.

As a result of both naturally occurring and human-assisted hybridization, B. oleracea plants can take a wide variety of forms. Over time, selection for edible leaves yielded cabbage, on which the leaves curl up to form a dense and compact “head”; kale, on which the leaves can be dense, green and bumpy, or purple and frilly on the edges, or some combination of the two; and collards, a classic Southern favorite with broad flat leaves ranging from yellow-green to deep blue or purple-green. Selection for edible flower buds created broccoli and cauliflower. And selection for edible stems resulted in kohlrabi, which resembles a purple or green alien spaceship when ready to harvest.

Broccoli heads opening up to reveal bright yellow four-petaled flowers

Despite their differences in size, taste and appearance, all of these vegetables are B. oleracea, not unlike how a golden retriever looks very different from a poodle or a border collie. The ancestor of all of these varieties can still be found growing wild in its native Europe along with feral cultivars that have escaped from human cultivation, although the taxonomic evidence increasingly suggests that the modern B. oleracea is descended from B. cretica in the eastern Mediterranean.

Once they have experienced a significant cold period, brassicas are primed to flower in late spring and early summer as temperatures warm. This process, known as bolting, marks the end of the harvest season for leaf crops, as plants shunt their energy away from large, tasty leaves to butter yellow four-petal cross-shaped flowers and, eventually, seeds. Even people growing broccoli or cauliflower must work quickly to harvest before the whole stalk or head becomes unpalatable, although the early pollinators will appreciate the ones that inevitably get away.

We donate the edible brassicas in the Discovery Garden to Iglesia Presbiteriana Emanuel, which distributes them to local families in need of food assistance. But we also grow many other B. oleracea plants purely for decoration in the winter months, taking advantage of their cold hardiness and attractive ruffled leaves to brighten the landscape when few other ornamental plants will thrive. Look for them in planters and pots throughout the Historic Gardens, and incorporated into the spring annual beds in the Terrace Gardens (see garden map here).

More Garden Talk Highlights

Photos from top: Purple kohlrabi plants in the Charlotte Brody Discovery Garden in late fall, before their stems have swollen, by Clarence Burke; bolting broccoli heads beginning to flower, by Karen Webbink; water droplets on curly purple kale, by Cathi Bodine.

close-up of water droplets on curly purple kale leaf