For many people, kohlrabi (Brassica oleracea) is one of 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.
Kohlrabi reaches harvest maturity 45 to 60 days after the seeds germinate. Ideally, you should plant it so it comes to harvest before average daytime temperatures exceed 75 degrees Fahrenheit. If you plan to harvest it as a fall crop, you can plant the seeds about 90 days before the expected first frost date.
|Botanical Name||Brassica oleracea|
|Common Names||Kohlrabi; German turnip|
|Plant Type||Herbaceous biennial|
|Mature Size||18 inches tall, 18 to 24 inches wide|
|Sun Exposure||Full sun|
|Soil Type||Rich, moist loam|
|Soil pH||Slightly acidic (5.5 to 6.9)|
|Flower Color||Pale yellow|
|Hardiness Zones||2 to 11 (USDA)|
|Native Area||Northern Europe|
How to Plant Kohlrabi
Kohlrabi is easy to grow, even for beginners. 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.
Plant kohlrabi seeds directly in the garden after the last hard freeze in spring, or plant in fall with enough time to harvest before the first hard freeze. Press the seeds 1/4 to 1/2 inch deep into the soil with 1-inch spacing. For row planting, space the rows 12 inches apart. Thin the seedlings to 4 inches apart after true leaves develop. Note: Spacing may differ for different plant varieties. For example, giant kohlrabi varieties, which are preferred for the longer fall season, should be seeded with 4-inch spacing and thinned to 12 inches between plants.
Kohlrabi needs a full day of sun to grow plump and develop its characteristic flavor. Because this 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 or fall soils. It typically needs 1 inch of rain or watering per week. 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.
Kohlrabi comes in nearly two dozen varieties with a range of different sizes, colors, flavors, shapes, resistance to disease, and length of storage life. You can select from heirloom or hybrid varieties as well.
You can choose between green and purple kohlrabi varieties based solely on your aesthetic preference. In either case, the bulb is white on the inside when cut or peeled. Some chefs say the purple varieties have a sweeter taste; a few favorite purple options include 'Kolibri', 'Rapid', and 'Purple Vienna'.
- 'Gigante' produces a large, tasty bulb, is disease-resistant, and can be kept stored for a long period of time.
- 'Early White Vienna' is a smaller "dwarf" variety that can remain in the garden longer without bolting to seed.
- 'Grand Duke' is the only kohlrabi to obtain an All America Selections Winner distinction, and it needs only 50 days to mature.
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 have complementary flavors and taste great together in soups or roasted vegetable medleys.
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 2 and 3 inches in diameter. Store bulbs in a cool, dry place until you are ready to eat them. The bulbs will keep for a month in the refrigerator.
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 introduction to a new vegetable taste sensation.
Kohlrabi leaves and stems are also edible and can be eaten cooked (like collared greens) or raw. Eat the greens immediately after harvest for the best flavor.
Prevent cutworms by spreading diatomaceous earth around young plants, or by using collars around plants. Handpick caterpillar pests like the cabbage worm. You can also remove egg clusters from the undersides of leaves.