Kale Seeds

Kale is a hardy biennial whose leafy rosette is familiar from markets, but the plant produces seed in its second year, when it sends up a tall stalk of yellow, four-petalled flowers. These develop into slender pods called siliques, each holding a row of tiny spherical seeds about 2 mm across. The seeds are reddish brown to nearly black, hard and smooth. Raw, they taste sharp and slightly peppery, similar to mustard or rocket, and become milder once sprouted. They are sold mostly as packets of garden seed, but also as sprouting seed in bulk for home sprouters and microgreen growers. Curly, flat-leaved, Lacinato and red-veined varieties all produce similar seed. Seed is best kept cool, dry and dark, where it stays viable for roughly four to five years.

Kale descends from wild cabbage, Brassica oleracea, a plant of the coasts of the Mediterranean and western Europe. Leafy, non-heading forms are considered among the oldest cultivated brassicas and were probably selected from wild populations in the eastern Mediterranean or Asia Minor. The English word kale is a northern form of cole, itself from the Latin caulis, meaning stem or cabbage. Borecole comes from the Dutch boerenkool, meaning farmer's cabbage, and the German Grünkohl simply means green cabbage. Because the plant needs a winter cold period before flowering, seed production has traditionally been tied to temperate climates, and seed-saving cultures in Britain, Germany and the Netherlands preserved many regional landraces.

Leafy kales were grown by the ancient Greeks and Romans, who valued them as winter greens, and writers such as Theophrastus and Cato described cabbage-like plants with curled leaves. In medieval Europe kale was one of the most common vegetables, because it survives frost and keeps producing when other crops fail. It was a staple of Scottish, Irish, Dutch and north German kitchens, and Scots once used the word kail for a meal or broth in general. Colonists carried kale seed to the Americas, and Russian traders introduced Siberian types to North America in the nineteenth century, which became a foundation for many hardy garden varieties. During the Second World War, British Dig for Victory campaigns encouraged home growers to plant kale for its reliability and vitamin content. After a long period as a humble vegetable, kale had a major revival in the early twenty-first century, and seed sales, sprouting seed and microgreen production grew along with it. Today seed is produced commercially in temperate regions of Europe, the United States and Oceania, and heirloom varieties are conserved by seed banks and gardeners.

Kale seeds are used first of all to grow the plant, whether for mature leaves, baby leaf salads or microgreens. Sprouted for a few days, the seeds give a crisp, peppery shoot that is added to sandwiches, salads and grain bowls. Microgreens harvested at one to two weeks have a tender texture and mild cabbage flavour. Brassica seed in general can be pressed for oil, and kale seed oil has been studied, although it is not a common commercial product. Gardeners save seed from their best plants to maintain local varieties, taking care that different brassicas do not cross with one another. Dried seed pods are also used in dried flower arrangements.

The seeds themselves are rarely eaten in quantity, so most nutrition research concerns the leaves and sprouts. Brassica sprouts contain glucosinolates, sulfur compounds that the body can convert into isothiocyanates, which are being studied for their possible role in cellular defence systems. Human evidence for disease prevention is still mixed and mostly based on observational studies of vegetable intake. Sprouts are a source of vitamin C and some minerals, but a handful of seeds does not make a meaningful dietary contribution. Eating a variety of cruciferous vegetables is associated with generally healthy dietary patterns.