An Ode to Brassicas: The Weeds That Feed the World
Brassicas may be the most successful weeds humanity ever adopted. Long before broccoli crowns sat beneath grocery store misting systems or kale became fashionable enough to headline restaurant menus, brassicas were wild plants clinging to rocky Mediterranean coastlines and disturbed fields. They were opportunistic plants: fast-growing, adaptable, and remarkably capable of thriving wherever. Today the brassica family includes some of the world’s most recognizable crops: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, bok choy, mustards, turnips, canola and more. Many of these vegetables are astonishingly close relatives. In fact, the first six plants on this list all cultivars of the same species: Brassica oleracea.
In many ways, the changes made to wild brassicas parallel another species humans profoundly reshaped: Canis lupus familiaris. A Pomeranian and a Great Dane are both dogs despite their radically different appearances. Brassicas follow a surprisingly similar path except instead of selecting ears or tails, humans selected leaves, stems, buds, flowers, and roots. Brassica leaves became kale. Enlarged buds became cabbage. Flower stalks became broccoli. Immature flower tissue became cauliflower. Axillary buds became Brussels sprouts. Swollen stems became kohlrabi. The list goes on.
Modern brassicas continue to evolve through breeding programs around the world. Some varieties are stable open-pollinated cultivars whose seeds can be saved generation after generation. Others are F1 hybrids, which are first-generation crosses created by breeding two carefully selected parent lines together. These hybrids are often developed for uniformity, disease resistance, bolt resistance, heat tolerance, shelf life, and flavor. Many grocery store brassicas are hybrids displaying what breeders call “hybrid vigor,” where offspring grow more vigorously or uniformly than either parent line. Because brassicas grow and reproduce relatively quickly, humans can adapt them at an unusually fast pace compared to many other crops.
One of the clearest examples of this is the Brussels sprout. Thirty or forty years ago, many people vocally disliked Brussels sprouts. But these days, people often say they “grew into” liking the vegetable. In most cases it is the vegetables themselves that have changed. Those older varieties contained significantly higher levels of bitter sulfur compounds. Plant breeders selected sweeter, milder, and more tender strains with lower bitterness and improved texture. Modern Brussels sprouts are often dramatically more palatable than earlier iterations.
One of the most remarkable traits of many brassicas is their frost tolerance. Kale, collards, Brussels sprouts, and winter cabbages often become sweeter after cold weather because the plants accumulate sugars and dissolved compounds that help reduce freezing damage within their cells. They make their own antifreeze! A frost can destroy a tomato overnight. A frost can improve the flavor of kale. Heat stress often pushes the chemistry in the opposite direction. During prolonged warmth or drought, brassicas develop stronger flavors, increased bitterness, and tougher textures.
Unlike chili peppers, whose heat lingers on the tongue, brassica heat is sharp, sinus-oriented, and fleeting. The characteristic pungency of brassicas comes largely from glucosinolates, sulfur-containing compounds common throughout the mustard family. When tissues are crushed or chewed, these compounds break down into sharp volatile chemicals called isothiocyanates.
This chemistry connects brassicas to radishes, horseradish, and true wasabi.
Wild brassicas still reveal their opportunistic ancestry. Across Napa Valley, spring erupts into yellow mustard blooms dominated by introduced Mediterranean species such as Black mustard. Widely considered invasive in many regions, these mustards can outcompete native plants, alter habitat structure, and contribute seasonal biomass to fire-prone landscapes. Yet these same plants have also become deeply integrated into California agriculture. In vineyards throughout Napa and beyond, mustard and other brassicas are commonly planted as cover crops between vine rows.
As cover crops, brassicas help reduce erosion, improve soil structure, increase water infiltration, support pollinators, and return organic matter to the soil. Some are even used in biofumigation, where compounds released during decomposition may help suppress certain soilborne pests and pathogens. ‘Nemagon’ mustard is planted where root-knot nematodes are an issue.
Brassicas remind us that the line between weed and crop is often surprisingly thin. Some now spread invasively across California hillsides while others are among the most carefully cultivated vegetables on Earth. Over thousands of years people have intentionally and unintentionally selected wild cabbage relatives for flavor, texture, vigor, and productivity, transforming them into an enormous diversity of crops. We owe a small thank you to the generations who saw potential in these resilient plants and helped turn a weed into one of humanity’s most important food families.
