For many people, kohlrabi is one those novelty vegetables you encounter in the produce aisle: It looks interesting, but unfamiliar, and you pass it by. However, kohlrabi is a versatile vegetable, and you can use it in recipes as a substitute for broccoli or cabbage. The name means cabbage-turnip, which is a clue to its flavor. When eaten raw, the young stems are crisp and mild. When cooked in stir-fries, soups, or casseroles, kohlrabi is like cabbage 2.0: vegetal, but slightly spicy.
Botanical Name: Brassica oleracea
Common Name: Kohlrabi; German turnip
Plant Type: Herbaceous biennial
Mature Size: 12 inches
Sun Exposure: Full sun
Soil Type: Rich, moist loam
Soil pH: Slightly acidic; 5.5-6.9
Bloom Time: Summer
Flower Color: Pale yellow
Hardiness Zones: 2-11
Native Area: Northern Europe
How to Grow Kohlrabi
Why take up precious garden space by growing kohlrabi? It's easy to grow, even for beginners. And, like other cruciferous vegetables, the flavor of kohlrabi is excellent the day of harvest, and begins to decline slightly each day thereafter. In fact, that kohlrabi you see on the grocery store shelf with slightly wilted leaves might even be a bit skunky, not a good intro to a new vegetable taste sensation.
Gardeners who can't wait to get a jump on the season should add kohlrabi to their early performers like peas and radishes. Kohlrabi is very cold tolerant, and ideally should be finished with its growing cycle before soil temperatures warm up.
Kohlrabi needs a full day of sun to grow plump and develop its characteristic flavor. Because kohlrabi is a fast, early-season vegetable, you may be able to plant it near deciduous trees that haven't leafed out yet.
Although kohlrabi isn't a root vegetable, it craves the same kind of growing conditions you would give your carrots or radishes: moist, rich, loam. Double digging or raised beds will yield kohlrabi bulbs with tender, non-pithy flesh.
Keep kohlrabi well-watered, which shouldn't be difficult in cool spring soils. For a nutrient boost, water with compost tea each time.
Temperature and Humidity
Like many cruciferous vegetables such as broccoli and Brussels sprouts, kohlrabi grows best in cool weather. When summer temperatures arrive, kohlrabi is done growing. Plants you didn't get around to harvesting will be prompted by warm weather to bolt, or produce flowers.
Kohlrabi is a heavy feeder. It's better to feed the plants continuously by enriching the soil with amendments that improve tilth than to add chemical fertilizers. Add manure at planting time, and side dress rows with compost until harvest.
Varieties of Kohlrabi
Gardeners can choose between green and purple kohlrabi varieties for the garden. In either case, the bulb is white on the inside when cut or peeled. Some chefs say the purple varieties have a sweeter taste. 'Grand Duke' is the only kohlrabi to obtain an All America Selections Winner distinction, and it only takes 50 days to mature.
Kohlrabi doesn't go through a very noticeable color change as it ripens, but you can rely on size as a determinant of harvest-readiness. Young bulbs and foliage have the best texture and flavor, so pull the whole plant when the bulbs are between two and three inches in diameter. Store bulbs in a cool, dry place until you are ready to cook or add to salads. The bulbs will keep for a month in the refrigerator.
Being Grown in Containers
Kohlrabi is not an efficient vegetable to grow in containers due to its large bulbs. You can grow a single specimen in a container as a novelty or to give away to a friend who wants to see what this vegetable is all about.
Growing from Seeds
Plant kohlrabi seeds directly in the garden after the last hard freeze. Press seeds into the soil. Space rows one foot apart, and thin seedlings to four inches apart after true leaves develop.
Prevent cutworms by spreading diatomaceous earth around young plants, or by using collars around plants. Hand pick caterpillar pests like the cabbage worm. You can also remove egg clusters from the undersides of leaves.
Kohlrabi vs Turnips
Kohlrabi and turnips are both cool season vegetables with edible bulbs. However, turnips, like carrots, potatoes, and beets, are true root vegetables. The bulb of the kohlrabi is not a root, and grows above ground. Kohlrabi and turnips are complementary flavors, and taste great together in soups or roasted vegetable medleys.