Brussels sprouts belong to the Brassica oleracea species, related to cabbage, kale, and broccoli. Growing your own seeds allows you to select for valuable traits, such as flavor, size, and hardiness in your local climate. This guide offers a step-by-step approach to successfully harvesting and preserving seeds, ensuring a consistent crop for future seasons.
Preparing Plants for Seed Production
Brussels sprouts are biennial plants, requiring two full growing seasons to produce viable seeds. In the first year, they focus on vegetative growth, forming the edible sprouts along the stem. The plant must survive a cold period to trigger the reproductive stage the following spring.
To ensure seed purity, select open-pollinated varieties, as hybrid seeds will not grow true to the parent. Select five to ten of the most vigorous and disease-free plants from your crop, marking them so they are not accidentally harvested. Isolate these plants from other flowering Brassica oleracea plants, such as cabbage or kale, to prevent cross-pollination, ideally by a distance of 1,000 to 1,600 feet.
The selected plants must undergo vernalization, requiring 10 to 12 weeks below 50°F. In mild climates where temperatures rarely drop below 35°F, leave the plants in the ground, protecting them with a thick layer of mulch or straw. For colder regions, carefully dig up the whole plants before the ground freezes.
After digging, the entire plant, roots and all, can be potted in slightly moist sand or potting mix. Store these potted plants in a cool, dark location, such as a root cellar or unheated garage, maintaining 34 to 39°F with high humidity. This cool storage mimics winter, preparing the plants to bolt and produce seeds when replanted the following spring.
Monitoring Second-Year Flower and Pod Formation
When the weather warms in the second spring, the overwintered plants will grow rapidly, transitioning to reproductive growth. The main stem, or stalk, will elongate significantly (bolting), sometimes requiring a stake for support. This tall stalk will be covered in small, bright yellow flowers, which rely on insects for pollination.
Once the flowers fade, the plant’s energy shifts to forming seed pods, technically called siliques. These pods initially appear small and green, resembling miniature pea pods, filled with developing seeds. Patience is required during this stage, as the seeds need time to fully mature and dry on the plant.
As the season progresses, the siliques will change color, turning from green to a tan or straw-brown. They must be completely dry and brittle on the stalk before harvest, as immature seeds are not viable. Closely monitor the plants, especially during hot, dry weather, because the pods can shatter easily and drop their seeds once mature.
Harvesting and Extracting the Seeds
Harvest when the majority of the seed pods have dried to a brittle, light brown and the seeds inside have turned dark brown. To prevent loss, cut the entire stalk when the pods are nearly dry, doing so over a tarp or container to catch any pods that may burst. Cut the stalks near the base of the plant, removing the roots and remaining foliage.
Bring the stalks indoors and hang them upside down in a warm, dry location with good air circulation for a final drying period of seven to fourteen days. This ensures the remaining moisture content drops sufficiently to prevent mold during storage. The stalks will become brittle once dry.
The next step is threshing, which involves separating the seeds from the dry pod material. Place the dried stalks into a large bag, such as a cloth sack or pillowcase, and vigorously roll a heavy object, like a rolling pin, over the bag or stomp on it gently. Alternatively, rub the dried pods between your hands to break them open and release the seeds.
After threshing, you are left with a mixture of seeds, broken pod pieces, and plant debris called chaff. To clean the seeds, use winnowing, which utilizes air movement to separate the lighter chaff from the heavier seeds. Pour the seed mixture slowly from one container to another in front of a gentle fan. The breeze blows away the lighter debris while the seeds fall cleanly into the receiving container. The resulting seeds must be thoroughly cleaned of all plant matter to ensure long-term preservation.
Storing and Testing Seed Viability
Once the seeds are cleaned and completely dry, proper storage is necessary to maintain viability for future planting seasons. Brussels sprout seeds remain viable for three to five years if kept in optimal conditions. Successful long-term storage requires cool, dark, and dry environments.
Store the seeds in an airtight container, such as a glass jar with a tight-fitting lid, or in a paper envelope inside a sealed plastic bag. Label the container clearly with the variety and the year of harvest to track viability over time. Keeping the seeds in a refrigerator or a dedicated cool, dark cupboard is ideal.
Before planting a new crop, especially if the seeds have been stored for a few years, test their germination rate. This simple viability test involves placing ten seeds on a damp paper towel, rolling the towel up, and sealing it inside a plastic bag to keep the moisture constant. Keep the bag in a warm location, and check the seeds after five to ten days for sprouts. If eight out of ten seeds sprout, the germination rate is 80%, indicating how thickly you need to sow your seeds.