The most popular cole crops--broccoli, cabbage and cauliflower--are members of the same botanical family. Less-popular members include Brussels sprouts, collards, kale, kohlrabi and turnips.
Seeds Versus Plants
Seeds for these vegetables can be sown directly in the garden one or two months before the last expected frost, but extreme temperatures may affect the quality of the harvest. Seeds can also be sown indoors five to 10 weeks before the last expected frost. Sow each seed roughly 1/4-inch deep in a one- or two-inch pot, and place on a sunny windowsill or under grow lights.
If you purchase plants instead of seeds, look for stout, healthy plants that are approximately six inches tall and have three or four leaves. To reduce the risk of transplant shock and to provide a good start for the plants, harden them off by leaving them outside during the day and bringing them in at night.
Planting
The cole crops are related, so it's not surprising that they prefer basically the same soil type. The soil should drain well and contain a fair amount of organic matter such as compost. These cool-season crops should have at least six hours of sun per day and should be planted three to six weeks before the last frost date so they will be ready to harvest before summer heat arrives.
The planting method for each of these crops is the same: Gently remove the transplant from its pot, tease the roots apart slightly and place the plant in the ground one to two inches deeper than it was growing in its container. Space the plants approximately 12 to 15 inches apart in every direction, in straight rows or staggered ones, to allow for more plants in a given amount of space.
Harvesting
Harvesting cole crops is slightly different from the procedure used for other types of crops. Once broccoli starts to develop, inspect the head daily and cut it when it is still nice and firm. Don't wait too long to harvest, or the head will begin to flower and much of the flavor will be lost. After the main harvest, don't forcefully pull the plant out of the ground; depending on the variety, a second harvest is possible from the side shoots.
With most varieties of cauliflower, the plant will have to be blanched as follows: When the head reaches the size of a golf ball, wrap the outer leaves around it and fasten them with a rubber band or some string. Inspect the head every day and harvest while still firm. Self-blanching varieties of cauliflower are available but may not be as tasty as those that require blanching.
Timing the cabbage harvest is slightly easier than for broccoli and cauliflower. Begin cutting the heads when they reach the size of a softball, or let them develop to full-sized heads. The easiest way to harvest is to cut the base of the head with a sharp knife.
Insect Control
A number of pests prey on cole crops, but most are easy to control without resorting to chemicals. The most widespread pest is the imported cabbage worm, which can be controlled with light spraying or dusting. If there are cutworms in the soil, consider wrapping cardboard around each stem before planting. Make sure the cardboard extends up from the base of the plant roughly two inches. Slugs can be a problem for cabbage too. To protect cabbage from slugs, lay a board in the cabbage patch and inspect the underside of it daily, destroying any slugs that gather there.
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