By Matt Gibson
Native to northwestern Europe (most likely Germany), kohlrabi is a flowering plant that belongs to the cabbage family. Originally grown in Europe, kohlrabi was brought to North America in the 19th century. Today, kohlrabi is cultivated all around the world for culinary purposes. Its flavor is described as juicy, crisp, and slightly sweet, like a mix between a radish and a cucumber. It can be enjoyed raw or cooked.
Depending on the variety, kohlrabi grows anywhere between six to 18 inches in height and 2 to 4 inches in diameter. Kohlrabi is a truly strange and unique-looking plant. Its massive, green or purple-green cabbage-like foliage has wavy, uneven edges and long petioles which emerge from thick, roundish stems. Cross-shaped clusters of white or yellow flowers sit atop its stalks.
The fruit which kohlrabi is cultivated for, is four to five inch long seed pods, which are filled with tiny seeds. The leaves and stalk of the plant are also edible, and are often used as a garnish, or plate decoration. Varieties of kohlrabi are split into two main categories based on the color of the stems and the skin of the fruit.
White kohlrabi varieties are typically light-green to cream colored, and purple varieties come in various shades of purple, from bright magenta to deep purple. Though the color of the skin can vary greatly based on the cultivar, all varieties have a creamy white flesh underneath.
Propagated by seed, kohlrabi can be planted two times per year, once in the spring, and again in the fall. Seed pods are typically ready for harvest in just 55 to 60 days after planting. Kohlrabi is rich in minerals such as copper, calcium, potassium and magnesium, as well as vitamin C, and multiple forms of vitamin B.
Varieties of Kohlrabi
Kohlrabi varieties are split into two different categories based on the color of their outer layer of skin, which is either white, or purple. White varieties are typically not truly white, but different shades of light green, whereas purple varieties range from light, lavender-like purple, to bright, magenta-purple, to dark purple.
There are over 30 different cultivars available to gardeners around the world.. Instead of listing every cultivar, we have gathered the most trusted varieties from each type to help narrow your list down to the best possible options of kohlrabi varieties on the market. Also, aside from color, we have listed varieties based on fruit size, quick maturing cultivars, bolt resistant varieties, and extended storage varieties so that you can better decide on the variety that’s right for you.
White Kohlrabi Varieties:
Grand Duke – The pale-green grapefruit sized bulbs of the Grand Duke cultivar take 50 days to mature. Grand Duke kohlrabi is the only cultivar to be awarded an All American Selections honor.
Kossack – This cultivar is simply massive. It produces light-green bowling ball-sized bulbs and tasty leaves which are similar to collard greens. Matures in 60 days. Sometimes spelled Kossak.
White Vienna – Ready to harvest in 60 to 65 days, White Vienna produces a flat bulb with pale-green to white skin. Very tasty.
Logo – Pretty, highly uniform plants used for baby vegetable production in Europe. Early white forcing type. Plant in springtime once temperatures reach 60 degrees F.
Early White Vienna – Ready to harvest in 50 to 58 days, this heirloom variety produces a flat, greenish-white bulb that is two inches wide. Early White Vienna is a dwarf kohlrabi variety, with medium stems, short tops and miniature leaves. Slow to bolt.
Korridor – Matures in 50 days, producing dark-green, erect leaves and white bulbs.
Purple Kohlrabi Varieties:
Kolibri – This quick growing Dutch variety matures in just 43 to 45 days. Produces large to medium-sized purple bulbs with almost fiberless white flesh. Tough stems make harvesting somewhat difficult. Stores well.
Rapid Star – Matures in 49 days, this crisp, cucumber-like bright-purple bulbed hybrid cultivar is slow bolting.
Purple Vienna – Also called Early Purple Vienna, this popular cultivar matures in 55 days. Purple Vienna produces flat bulbs with purple skin and creamy white flesh.
Azur Star – Similar to Logo, the Azur Star is a highly uniform plant which should be sown once temperatures reach 60 degrees F. Produces blue-skinned bulbs. Bolt resistant.
Medium Sized Bulbs:
Kossak, listed above in the white kohlrabi varieties, forms incredibly large bulbs. Though Kossak is a favorite for some gardeners due to its tasty leaves and tender flesh, many gardeners prefer varieties that produce medium-sized bulbs. Here are a few of the best medium-sized bulb varieties.
Dyna – Ready for harvest in 60 days, Dyna is an open-pollinated variety. Produces eight to ten inch bulbs that are sweet and tender. Similar to Superschmelz, but with purple skin. Better when planted in summertime for an autumn harvest.
Tianstsin Strain – Produces medium-sized green bulbs with white flesh. From northern china.
Quickstar – Ready for harvest in 49 to 59 days, this early-maturing hybrid produces flat, round, smooth, six-inch bulbs with pale green skin and dark-green leaves. Plants are slow to bolt.
Early White Delicacy – Matures in 50-65 days, harvest when swollen stem is tennis ball-sized.
Peking Strain – From northern China. Produces pale-green bulbs with white flesh.
Longer Storage Kohlrabi:
Kossak – See above.
Gigante – Matures in 62 to 130 days, this massive Czechoslovakian heirloom forms 10-inch diameter, 10 pound bulbs that do not get woody even if the plant bolts. Leaves can be used like kale. Plant during the spring for a fall harvest. Root maggot resistant. Stores well. Also known as Gigant and Gigant Winter.
Superschmelz – Plant in the summer for an autumn harvest. This open-pollinated variety produces eight to ten inch bulbs that stay sweet and tender. Matures in 60 days.
Kolibri – See above.
Quick Maturing Kohlrabi:
Winner – Matures in 45 to 57 days. Winner is a hybrid variety that forms pale-green, 18-ounce, semi globe-shaped bulbs.
Kolibri – See above.
Eder – Ready for harvest in just 38 days, Eder produces tender bulbs with excellent flavor.
Sweet Vienna – Matures in 45 days, this variety produces three-inch bulbs with a sweet flavor.
Granlibakken – Ready for harvest in 45 days, this cultivar produces light to medium-green bulbs that hold well without becoming woody.
Bolt Resistant or Slow To Bolt Kohlrabi:
Rapid Star – See above.
Early White Vienna – See above.
Azur Star – See above.
Quickstar – See above.
Growing Conditions for Kohlrabi
Kohlrabi is a cool weather vegetable that is quite cold tolerant. It is hardy to USDA zones two through 11 and should be added to the garden with early starters so that it is finished growing and ready for harvest before the soil temperatures start to warm up. Though it is not a root vegetable, kohlrabi prefers very similar growing conditions to root vegetable crops like radishes and carrots.
Kohlrabi prefers a full day of sun exposure and a nutrient rich, consistently moist, loamy soil type with a slightly acidic pH range between 5.5 and 6.9. Planting your kohlrabi in raised beds, or taking the time to double dig the soil before planting will help assure you of high-quality bulbs. Keep the soil moist and if possible, give your kohlrabi a nutritional bonus with diluted compost tea when watering.
Be sure to harvest all of the bulbs before the weather starts to warm up, as kohlrabi plants will bolt in warm weather, though there are some varieties that are more bolt resistant if you live in a warm weather region. If you let one of your kohlrabi plants bolt, its bulbs will turn woody and bitter very quickly.
Kohlrabi is a heavy feeder and your plants will grow more vigorously if given ample amounts of nutrients throughout the growing season. Feeding your kohlrabi plants with organic soil amendments is recommended over using commercial fertilizers. Amend the soil with lots of well-rotted manure prior to planting and continuously enrich the soil by side dressing each row of kohlrabi with compost up until the bulbs reach full maturity. And, as mentioned above, water with a diluted compost tea for an additional boost.
How to Plant Kohlrabi
Four to six weeks before you plan to move them outside, start your kohlrabi plants indoors. Kohlrabi loves cool weather, and will perform well if transitioned outdoors with early starters like radishes and peas, however, you can also plant them directly into the garden after the last hard freeze. Prepare the beds by double digging with lots of well-rotted manure. Remove clumps, stones, and any plant debris from previous seasons.
If you’re starting your kohlrabi seeds indoors, plant them one-fourth to one-half inch beneath the soil spaced three to five inches apart in a small container or seed starting tray. If planting directly outdoors, press seeds into the soil about a half-inch deep in rows spaced 12 inches apart. Thin seedlings down to four or five inches apart after the second set of leaves sprout. Keep the soil well watered. Because of the large size of the bulbs that it produces, kohlrabi is not a good candidate for container gardening.
Care for Kohlrabi
Keeping the soil around your kohlrabi plants moist and nutrient rich are the keys to successful kohlrabi cultivation. Providing a consistently even supply of water will insure sweet, tender bulbs. If the soil doesn’t get enough moisture, the bulbs and stems will become woody, fibrous, and tough. Work in compost throughout the season by side dressing each row. Give a boost to your kohlrabi plants with diluted compost tea, if possible.
How to Propagate Kohlrabi
Propagate kohlrabi by seed by either starting indoors four to six weeks prior to the last hard freeze in your area, or plant directly into the ground after the last hard freeze in your area passes.
Garden Pests and Diseases of Kohlrabi
Cutworms are one of the few garden pests that trouble the kohlrabi plant. Prevent cutworms by placing collars around your plants or by spreading out Diatomaceous Earth (DE) when the plants are young. Check your plants occasionally for cabbage worms. Hand pick them off and crush them. Also look for their eggs, which they deposit in clusters on the underside of leaves. They can be destroyed simply by lightly rubbing your thumb over the underside of the leaves.
How to Harvest Kohlrabi
It’s rather tough to tell when your kohlrabi is mature, as there is no color change to indicate ripeness, so you have to rely on the size of the bulb to determine when to harvest. Luckily, young bulbs and young leaves have the best flavor, so depending on the variety and the expected size of the cultivar that you are growing, harvest when it reaches the expected size. Most medium-sized kohlrabi bulbs should be harvested when the bulbs are between two and three inches in diameter.
How to Store Kohlrabi
Store kohlrabi in a cool, dry location until you are ready to use them. Bulbs will stay fresh and crisp in the refrigerator for up to one month. If you want to freeze your kohlrabi, it is best to blanch it first, unless you are planning to use it in just a few days. Blanch whole kohlrabi bulbs boiling them for three minutes, and half-inch cubes for one minute. Cool quickly. Drain and pat dry with a paper towel and then store in an airtight container leaving about a half-inch of headspace at the top of the container.
Kohlrabi might be a strange looking vegetable, but it is a wholesome, nutritious, tasty treat that is definitely worthy of some space in your garden beds. It can be used to replace broccoli or cabbage in recipes, it can be eaten raw or cooked in a variety of methods. Kohlrabi pairs well with radishes in soups and stews. The name kohlrabi actually means cabbage-turnip, which it was probably titled in a nod to its flavor. It has the subtle spiciness of the turnip combined with the green cruciferous vegetable crunch of fresh cabbage. What’s not to like?