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. 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 one-inch spacing. For row planting, space the rows 12 inches apart. Thin the seedlings to four 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 four-inch spacing and thinned to 12 inches between plants.
Kohlrabi Care
Light
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.
Soil
Although kohlrabi isn’t a root vegetable, it craves the same kind of growing conditions you would give carrots or radishes: moist, rich loam. Double digging or raised beds will yield kohlrabi bulbs with tender, non-pithy flesh.
Water
Keep kohlrabi well-watered, which shouldn’t be difficult in cool spring or fall soils. It typically needs one 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.
Fertilizer
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 Varieties
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.
Harvesting
Kohlrabi doesn’t go through a very noticeable color change as it ripens, but you can rely on the 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 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 collard greens) or raw. Eat the greens immediately after harvest for the best flavor.
Common Pests
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.
