How to Plant, Grow, and Save Seeds from Cabbage (Brassica oleracea)
Cabbage varieties come in a spectrum of colors, from light green to dark purple. The scientific name of cabbage is Brassica oleracea, a species that also includes broccoli, cauliflower, kale, and Brussels sprouts.
Sow cabbage seeds indoors 4-6 weeks before transplanting seedlings outdoors. Sow seeds ¼” deep. Cabbage seeds will germinate in 7-12 days. Transplant cabbage seedlings outdoors just before the last frost. Space cabbages at least 24-36” apart in even spacing or 12-14” apart in rows spaced 36-44” apart.
Cabbage can suffer from a number of pests and diseases including flea beetles, cabbage moths, aphids, leaf miner bugs, slugs, and black rot. Early season insect pests, such as flea beetles, can be deterred by growing transplants underneath row cover.
Cut the head at the base of the plant with a harvesting knife or pruning shears as soon as the cabbage head feels solid. Trim off the loose outer leaves and store heads in a cool place.
Eating and Storing
Raw cabbage can be used in fresh salads like coleslaw. It can also be enjoyed roasted, braised, stewed, and stir fried. Cabbage is often fermented to make sauerkraut and kimchi. Cabbage will keep for about four months at a temperature between 32-40 °F and a relative humidity of 80-90%.
Cabbage is a biennial crop. Biennials typically do not flower in their first growing season. They must first experience cold weather before they flower, set seed, and die in their second growing season.
When saving seeds from cabbage, separate varieties by at least 800 feet in their second year of growth. To ensure viable seeds, save seeds from at least 5 plants. To maintain a variety over time, save seeds from between 20-50 plants.
To save seeds from cabbage, first decide how you will vernalize your plants. Vernalization can happen in the field or in storage. Overwinter cabbage in the field if you will have 10-12 weeks of cool weather (around 50 °F) without regular temperatures below 35 °F.
When plants cannot be successfully overwintered in the field, they can be vernalized in storage. Before the first frost, dig up the entire plant, roots and all. Trim off outer leaves but keep the cabbage head intact. Replant these trimmed plants into containers filled with slightly moist potting mix or sand. Then, find a place to store your plants. The optimum storage conditions for cabbage vernalization ranges from 34-39 °F and 80-95% relative humidity. A traditional root cellar is ideal but garages, sheds, and other unheated structures work well in some climates.
In the spring, when the soil can be worked, replant cabbage in your garden. Space plants at least 36” apart. Staking the plants is recommended. After flowering in their second year of growth, mature seed pods become dry and turn brown as the seeds inside also mature and brown. As with many of the brassica crops, the window of time for an optimal harvest may be short as mature pods will begin to shatter and bird predation can become a problem.
Seeds can be gathered by cutting entire branches or by harvesting whole plants. Because of this species’ tendency to shatter, the harvested material should be placed on drop cloths or in containers to prevent seed loss. Branches of mature fruits can be threshed by rubbing the pods between one’s hands or by flailing the brittle pods against any surface that will cause fruits to break open. If the pods are dry, they will release their seeds easily when threshed.
Store cabbage seeds in a cool, dark, and dry place in an airtight container to keep out moisture and humidity. Properly stored cabbage seeds will remain viable for several years.