Brussels Sprouts (Brassica oleracea var. gemmifera)

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Brussels sprouts are widely grown in temperate zones for their edible axillary buds which are reminiscent of miniature cabbages. Although native to the Mediterranean region with other cabbage species, Brussels sprouts first appeared in northern Europe during the 5th century, later being cultivated in the 13th century near Brussels, Belgium, from which they derived their name.

They are rich in vitamin C and vitamin K, with moderate amounts of B vitamins. Like other brassicas such as broccoli, they contain sulforaphane, a phytochemical under basic research for its potential biological properties. Levels of suforaphane are better preserved when Brussels sprouts are steamed rather than boiled.

Growing recommendations

Brussels sprouts are biennial plants (commonly grown as annuals) that prefer environments with a full sun exposure as well as a well-drained, loamy, fertile and alkaline soil. They require a very long growing season (~90 days) and are difficult to grow in hot summer climates. Plants, especially the late harvesting cultivars, are hardy to about -10° C.

In colder climates, Brussels sprouts can be started indoors around early May then transplanted in the garden in mid-June or about four months before the first fall frost. In warmer climates, fall planting is preferred, but direct seeding is possible in mid-summer for a late fall or early winter harvest if the conditions permits it. The seeds should be adequately spaced out, covered with 1 cm of soil, and germinate best at about 20° C within 5-10 days. Plants meant for seed production should be thinned out to 30-60 cm.

Pollination, crossing, and isolation

Brussels sprouts are in flower from May to August, with the seeds ripening from July to September. The species bears hermaphrodite flowers, having both male and female organs, that are pollinated by bees. They are self-incompatible and must indeed be insect or hand-pollinated in order to produce viable seeds. As strong outbreeders, they will need to be isolated accordingly with appropriate techniques in the event several varieties are grown simultaneously in the garden or in the vicinity. Brussels sprouts will indeed easily cross with each other, as well as with all other varieties within the Brassica oleracea species. If spatial isolation is not possible, advanced seed savers may want to use alternate day caging with or without the introduction of pollinators.

General seed saving guidelines (harvesting and processing)

As a biennial plant, Brussels sprouts will require two seasons to produce seeds and must undergo vernalization in order to flower. In mild climates, they can be left outside in the garden to overwinter. In cold winter areas, selected plants will need to be carefully dug out in the fall and stored in sawdust in a humid place (80-90%) at about 0-4° C for 2-3 months. Some losses are to be expected. Overwintering them in a greenhouse can also be an option. They are replanted in the following spring, where they will produce flower stalks and seedpods.

As they mature, the pods will start to dry and turn brown. However, if the plants are allowed to fully dry in the field, one run the risk of them shattering, which might attract birds and result in important losses. Several hand harvests can be conducted over several weeks as the seeds dry or the whole mature stalks can be cut and dry further on tarps in a protected area for a few days (which is best). The stalks can then be threshed by placing them inside a bag and trampling over it, or the seedpods stripped and rubbed gently to crush them and release the seeds. The threshed pods can be cleaned by winnowing and/or with the help of screens. If a source of wind is used to remove the chaff, ensure that the processing area is covered by a tarp, which will help recover any seed that has been accidentally blown out of the winnowing container. Do not forget to clean it after each new variety to avoid any accidental mixing.

Brussels sprouts seeds will remain viable for an average of five years when stored under optimum conditions.