Broccoli and Cauliflower (Brassica oleracea var. italica, var. botrytis)

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Broccoli (Brassica oleracea var. italica) is a commonly grown edible plant belonging to the cabbage family (Brassicaceae) whose large flowering head, stalk and small leaves are consumed as a vegetable. Classified in the same species, cauliflower is a different but closely related cultivar group (var. botrytis) whose only the head is eaten. Broccoli and cauliflower are the result of centuries of selection in the Mediterranean region which slowly developed to the several colored varieties that are cultivated today.

Broccoli is known to be a rich source of vitamin C and vitamin K, better preserved when it is steamed rather than boiled. Cauliflower also contains vitamin C in high amount, with moderate levels of several B vitamins and vitamin K.

Growing recommendations

Both broccoli and cauliflower are biennial, frost-tolerant plants (but typically cultivated as annuals when grown for consumption), planted in early spring for a summer harvest or late summer for a fall harvest in temperate areas with mild winters. They are suitable for light (sandy), medium (loamy) and heavy (clay) soils provided they are moist and well-drained soils with a neutral pH. While broccoli and cauliflower prefer full sun, they can be grown in partially shaded areas and tolerate maritime exposure.

Depending on the climate and season, both can be direct seeded (at a depth of 1.5 cm) then covered or started in a greenhouse then transplanted. Seeds will usually germinate at an optimum temperature of 20° C in about a week. Plants meant for seed production should be thinned out to 40 cm for broccoli and 60 cm for cauliflower.

Pollination, crossing, and isolation

Both broccoli and cauliflower flower from May to August with the seeds ripening from July to September. The plants bear hermaphrodite flowers, having both male and female organs, that are pollinated by bees. 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. Broccoli and cauliflower will indeed easily cross with each other, as well as with all other varieties within the Brassica oleracea species, except Chinese cabbage (Brassica rapa, subsp. pekinensis and chinensis). 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 biennial plants, both broccoli and cauliflower will require two seasons to produce seeds and must undergo vernalization in order to flower. However, some shorter season varieties might flower and produce seeds in one season. In mild climates, broccoli and cauliflower 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.

Broccoli and cauliflower seeds will remain viable for an average of five years when stored under optimum conditions.