Cabbage can be grown for late spring/ summer harvest, or for fall harvest. For a spring crop, sow seeds indoors 6-8 weeks before your last frost date, and plant seedlings out after the last frost. Plant seeds ¼ inch deep. Transplant your seedlings out after your last frost date. Space them 12 to 24 inches apart, depending on the size of head you’d like them to produce. Cabbage prefers full sun, but can tolerate part shade, particularly if you are growing in a hot climate. Try not to plant cabbage in the same spot where other brassica crops have been planted in the previous three years.
For a fall crop, start cabbage seeds in mid to late summer. If your summer temperatures are fairly mild, you can direct-seed your fall cabbage outdoors. Sow seeds about ¼ inch deep and 4 inches apart, then thin the seedlings to at least 12 inches apart once they’ve developed their second set of true leaves. If your summers are scorching, you may have better success starting your fall cabbage crop either indoors or in the shade, and transplanting the seedlings out in the garden after temperatures begin to cool down. Chinese (napa) cabbage varieties are especially good for fall plantings, as they tend to bolt much more easily in the spring.
It’s a good idea to mulch around your cabbage plants to keep the soil moist and regulate weeds. The roots of brassica crops tend to be shallow and easily disturbed by weeding. Watch for cabbage loopers and aphids, and either pick them off or spray your plants with soapy water or Bt as needed. If you have lots of trouble with pests, keeping your cabbage plants under light row cover can help. Once the heads have reached the desired size, harvest your cabbages by cutting at the base of the head with a sharp knife. After harvesting, pull up the rest of the plant and compost it.
Cabbages (Brassica oleracea) are an insect-pollinated biennial. They will flower and go to seed in their second season after overwintering. If you are growing in a fairly mild climate, you can overwinter cabbage plants under row cover. If your area experiences regular hard freezes, you may need to dig up the plants you want to save seed from and keep them in pots in cool place such as a root cellar for the winter, then plant them back out as the soil becomes workable again in early spring. An important note: leave the head intact on any cabbage plants you want to use for seed saving. You can’t have your cabbage (seed) and eat it too! The flower stalk of a cabbage plant emerges from the central growth tip, which is in the middle of the head.
The seeds are mature when the seed pods turn brown. Mature pods will shatter and drop their seeds quickly, so it’s best to pull up the plants and bring them indoors to finish drying on tarps once many of the pods begin to turn brown. Thresh the seeds from the pods by stomping on them on a tarp, or hitting the stalks against the inside of a clean trash can, or smashing the seed pods inside a pillowcase. Winnow out the chaff by pouring seeds and chaff from one container to another in front of a box fan set on low. Once you have clean seed, make sure that it is fully dry before storing it in an airtight container in a dark, dry, and cool location.