Considered the powerhouse of vegetables, the genus Brassica includes such nutrient-rich greens as Brussels sprouts, cabbage, broccoli, cauliflower, turnips, collards, kale, kohlrabi, rutabagas, mustard and bok choy. What sets the Brassicas apart from other groupings is that they represent vegetables that are harvested for edible roots, stems, flowers and leaves. No plants grow like clockwork, and setting a maturity date on the calendar is no guarantee your vegetables are ready. So keep a close eye on your garden so you’ll know when the time is right.
Harvest your cabbage when the head of it is filled out and firm. This usually means the head is anywhere from 4 to 10 inches in diameter depending on the variety. The firmness, however, should tell you it is ready.
Slice across the base of the stem immediately below the head. If you're unsure where to cut, or cannot see it well, then cut just above the soil level.
Pull up the remaining root system and plant more cabbage or other vegetables in its place. Try succession planting so you’ll never have too much cabbage to harvest, yet enjoy fresh cabbage throughout the growing season.
Broccoli and Cauliflower
Wait for broccoli to have a large head with tight, green buds. Cauliflower should have a firm head to it with a diameter anywhere from 4 to 8 inches across.
Cut horizontally across the main stem, just below the heads to harvest. Be sure your knife is sharp because the main stem can often be thick and resistant.
Harvest your broccoli a second time after secondary shoots have spread out from the cut main stem. While these secondary shoots will make smaller heads, there will be more of them than the first initial head of the plant.
Cut ready Brussels sprouts from the base of the stem after they are 1 to 1-1/2 inches in diameter.
Working up the stalk, remove only bottom level sprouts that are ready, a few at a time from each plant. This leaves the higher-up sprouts time to mature and grow.
Force the plant into maturity if you want to harvest all of your sprouts at once by cutting off the top 6 inches of the plant a month before you expect to harvest. A month later, simply remove all sprouts from the stalk.
Collards, Kale, Mustard and Bok Choy
Collect the leaves of collards, kale, mustard and bok choy from the outside first by cutting them from the main stalk. Collards and kale should be 10 to 12 inches tall, mustard 6 to 8 inches long, and bok choy needs to be at least 5 inches tall before the first harvest.
Continue to harvest occasionally as needed without ever stripping the plant of all its leaves. Occasional harvesting will allow the plant to continue to produce and subsequent harvests can come from the same plant throughout the growing season.
Pull up the entire plant of mustard before the weather becomes continually hot. While bok choy shouldn’t have more than six hours of direct sunlight a day in exposed, hot spaces for best performance, collards should continue to do well through the summer and into the light frosts of fall. If you cut your kale to 2 inches tall just before it bolts, it will grow two head sprouts in a few weeks.
Kohlrabi, Rutabagas and Turnips
Pull up the entire bulb when kohlrabi stems have reached 2 to 3 inches in diameter. Rutabagas should be pulled when the tuber is 3 to 5 inches in diameter and the tops are a foot tall. Turnips should also be 1 foot tall, but with a tuber 2 to 3 inches in diameter.
Use a garden fork if it feels like the greens might separate from your tuber when pulled. Be sure to slide the fork into the dirt a few inches away from the bulb and let it run under the soil well below where you assume the base of the bulb is to avoid damaging it.
Harvest only the greens of turnips by thinning the outside leaves and leave the central growth bud to sprout again.