Kohlrabi looks like the space alien of vegetable crops: It develops a big, fat bulb (actually a swollen stem) on the surface of the soil, and from that come antenna-like stems topped with leaves. Despite its strange appearance, kohlrabi is a terrific addition to a salad or stew, and its leaves are edible, too. This member of the cabbage family comes in three colors: green, white, and reddish-purple. All have a similar flavor and the same appealing crunch.
Kohlrabi is very fast growing. The bulbs are usually ready to eat in just eight weeks or less. They are best picked when they are the size of a large orange; if you wait too long they can become tough.
Because the seeds germinate well outdoors and the plants grow quickly, there is little point in starting seedlings indoors. Plant seeds about half an inch deep and 3" apart, thinning to 6" apart once the bulbs get to be a couple inches in diameter. Like most in the cabbage family, the plants are fairly frost-tolerant and prefer cool weather. Kohlrabi can be planted four weeks before the last frost, and again in late summer for a fall crop.
Kohlrabi grows best in full sun and rich soil that drains well but stays lightly moist. If it is deprived of water, it tends to split, or develop cracks. Prevent this by amending the soil with compost at planting time and watering during dry times. A layer of mulch on the soil surface will help, too. Some of the new cultivars have been bred to resist splitting.
Like other members of the cabbage family, the leaves of kohlrabi are attractive to a number of insect pests; flea beetles, aphids, cabbage loopers and slugs. A layer of garden fabric (row covers) placed over the young plants will prevent those pests from getting to them.
Kohlrabi is rich in potassium and vitamins A and C. It stores well in the refrigerator or in a cool, 35-50 degree F. root cellar with high humidity. Stored properly, it will keep for three months or longer.