Growing Kohlrabi: Time To Grow Alien Veggies
Much of the United States is unfamiliar with growing kohlrabi. We explore this forgotten and delicious vegetable and how to grow it at home!
Contents
Kohlrabi is a member of the cabbage family. The name Kohlrabi comes from two German words: Kohl and Rube. While kohl means cabbage, rube means turnip. So the name literally means “cabbage turnip” in German! Today, we’ll be discussing growing kohlrabi in your own garden.
Kohlrabi originated from northwestern Europe. Today this odd-looking plant is found worldwide. It is cultivated as a food source rich in vitamin C and vitamin B. It’s also an excellent source of minerals, especially copper, magnesium, potassium, and calcium. The calorie count is low, with only 27 calories per 100g of raw kohlrabi.
Fresh, young kohlrabi has a sweet taste and a juicy, crispy texture. The flavor profile resembles a mix of cabbage and radish. The bulb, stalks, and leaves can all be eaten, but its skin is a bit tough and is generally removed. It can be eaten raw or used in salads, soups, or meat dishes.
This alien, bizarre vegetable may not resemble anything we usually eat, but that’s part of its charm. Whether Early White Vienna, green, or purple kohlrabi (like Early Purple Vienna), it’s an unusual addition to your garden beds… and a delicious one, too. So let’s talk about how to grow kohlrabi so you can enjoy this brassica in your garden and kitchen!
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Quick Care Guide
| Common Name(s) | German turpin, cabbage turnip, kohlrabi, su hào, kalerab |
| Scientific Name | Brassica oleracea var. gongylodes, Gongylodes group |
| Days to Harvest | 55 to 60 days after sowing |
| Light | Full sun, at least 6 hours per day |
| Water | Consistent soil moisture, about 1” per week |
| Soil | Rich, well-worked, well-draining soil with high organic content |
| Fertilizer | Composted cow manure, 10-5-5 fertilizer |
| Pests | Cabbage aphids, beet armyworm, cabbage worms, cabbage loopers, cutworms, flea beetles |
| Diseases | Alternaria leaf spot, black rot, downy mildew, powdery mildew |
All About Kohlrabi
The botanical name of kohlrabi is Brassica oleracea, and it’s part of the Gongylodes group and the cabbage family. If that seems like a mouthful, you can just call it by its common name, kohlrabi. It has a myriad of names in other languages, from su hào in northern Japan to kedluben in the Czech Republic. While the names are unusual, so is the plant itself!
What does a kohlrabi look like? Kohlrabi has a broad, roundish bulb with protruding stems. These kohlrabi stems reach anywhere from 6 to 18 inches tall, depending on the variety (unless we’re talking about giant kohlrabi varieties). Big, cabbage-like leaves with long petioles and wavy edges top each stem. The plant also produces flowers that are white or yellow and bloom in clusters on top of flowering stalks.
Kohlrabi is not a root vegetable, as all portions are edible, but the bulb is most commonly used in food. The main producing countries include Russia, China, India, and Korea. If you’re looking to plant kohlrabi in your vegetable garden, select from varieties such as Early White Vienna, Grand Duke, Gigante or Superschmelz, Purple Kohlrabi, and White Danube. They all vary slightly in exterior color, but the interior flesh is white for all kohlrabi varieties.
How To Plant Kohlrabi
The first step to growing kohlrabi is planning the best start. After all, it won’t grow well if it’s in the wrong location or if you plant kohlrabi at the wrong time!
Kohlrabi plants do well in cool weather conditions. The best time to plant kohlrabi seeds is 3 to 4 weeks before the predicted date for the last spring frost or earlier if you want to start seeds indoors. These vegetables take 45 to 60 days to mature. As kohlrabi can survive an early frost, warm-climate dwellers can sow seed for a summer or early fall crop in the cool weather of autumn. Warm locations like southern California can grow kohlrabi for a winter harvest too! Those areas with cool weather in summer can plant and grow kohlrabi for a fall harvest or winter harvest.
Sow seeds directly in the ground or start seeds indoors. Live kohlrabi plants should be transplanted into the garden a little before the final frost date, so begin hardening them off to the outdoor temperatures in advance. Your seedlings should be four to six weeks old at the time of transplant for best success.
Select a full-sun location to plant kohlrabi. While kohlrabi can be grown in containers, it may require more frequent watering and fertilization, so keep that in mind. We recommend growing yours in raised beds with fertile, well-draining soil.
When you’re growing kohlrabi, space plants 9-12 inches apart in rows spaced at least the same amount of inches apart. However, square-foot gardeners have been known to use intensive kohlrabi plant spacing, with as many as nine plants per square foot. This usually leaves only about 3 inches apart between individual plants, but it can really increase the quantity you’re able to plant.
For sowing kohlrabi seeds, plant ¼” deep with just a light dusting of soil over top. Once they’ve germinated, thin to your preferred number of inches apart by cutting off excess sprouts with pruning snips.
Growing kohlrabi from transplants starts similarly, but once you have 4-6 week-old transplants of kohlrabi growing, put them out into the garden when they’re hardened off. Plant at the same depth they were in their pot. Avoid planting kohlrabi where you’re allowing an inch deep of soil to build up around the kohlrabi bulb base; for these plants, their bulb actually forms above ground, with only their cabbage-like roots underneath. Space at your preferred kohlrabi spacing as covered above.
Kohlrabi Care
So now we’ve covered planting, and you might ask how to grow kohlrabi for the best results. Let’s talk about elements like garden soil and other important factors for good growth!
Sun and Temperature
Kohlrabi grows best in full sun… the more, the better. Make sure you choose a spot in your garden that receives at least 6 hours of full sunlight every day. The ideal temperature range for growing Kohlrabi is 40°F to 75°F (4.4°C to 23.9°C).
The plant is heat-sensitive, and conditions that are too warm can make the kohlrabi bulb turn woody. Kohlrabi grows poorly in temperatures higher than 75°F (23.9°C) during the harvesting season. Kohlrabi can be grown in USDA growing zones 3 to 10. A spring for fall, and even late winter harvest is possible.
Watering and Humidity
When considering how to grow kohlrabi, remember these plants need moisture to supply those bulbs, stems, and leaves. Keep the soil evenly moist at all times, applying more water when the first inch of soil dries out. A soaker hose is ideal for watering your kohlrabi plants.
Kohlrabi grows best with an inch of water per week, but if the weather’s rainy, you can skip watering. As long as you keep the soil evenly moist, you’re good.
Soil
Kohlrabi needs fertile and well-drained soil to grow and produce healthy stems, leaves, and its bulbous base. Mulch the soil with plenty of organic matter, like composted manure for added nutrition and water absorption to keep the soil moist. Loose, well-worked soil is best for your kohlrabies to truly shine! The ideal soil pH level for growing kohlrabi ranges from 6.0 to 6.8.
Fertilizing Kohlrabi
Fertilizing kohlrabi is a little tricky as they’re heavy feeders. Start with rich soil, to begin with, and side-dress every few weeks with well-rotted cow manure. Alternately, begin with rich soil but opt for regular fertilization using a nitrogen-rich fertilizer. A 10-5-5 should suffice, but follow manufacturer’s instructions for the frequency of application.
When you’re growing kohlrabi in containers, regular fertilization is a must, as they will drain the soil of nutrients. They have shallow but large root systems, so apply your fertilizer in a ring around the plant but don’t make contact with the bulbous stem base. The same is true of in-ground fertilization, but there’s less risk of water washing the fertilizer back against the plant in a normal bed setting.
Liquid fertilizers are also an option, but only if your soil retains the dissolved nutrients. If you have ample supplies of organic matter in the soil, regular applications of liquid fertilizer will work.
Pruning
Pruning is not necessary when growing kohlrabi. The only time you’ll cut the plant is when you harvest.
Kohlrabi Propagation
Kohlrabi is typically propagated through seeds only. Other methods of propagation don’t result in good, healthy plants. Opt to grow kohlrabi from seeds from a reliable supplier.
Harvesting and Storing
The green leaves, long stems, and bulbous base of kohlrabi are all harvestable. Growing kohlrabi can be a lot of fun, and so is the time when you harvest kohlrabi for future meals! Whether you’re looking at a fall harvest or spring harvest, here’s how to do it. We’ll discuss how to store kohlrabi too.
Harvesting Kohlrabi
While we’ve covered how to grow kohlrabi, harvesting can be a bit tricky by comparison as it relies on what you plan to use. When you harvest kohlrabi, know that each portion has slightly different timing. Harvest kohlrabi leaves and stems from the outer portions of the base first, cutting off stems cleanly with pruning shears to reduce the risk of damage to the bulb. Leave the inner, uppermost stems and leaves intact until you’re ready to harvest the base as well.
Harvest kohlrabi leaves one by one at need. Stems should be at least the size of your finger or larger, although most harvest when the stems are about an inch in diameter.
Once you grow kohlrabi to a size of 2-4 inches, you can harvest kohlrabi bulbs. More mature kohlrabi bulbs become woody with age. We recommend a good median size of about 3 inches. To harvest the base, remove the entire plant from the soil and cut off the root ends. Clip off leaves and stems flush with the bulb.
Storing Kohlrabi
For best storage, place your kohlrabi harvest in a cold, moist location. Ideal conditions would include 95% relative humidity at 32° F to 40° F (0° C to 4°C). The closest approximation is to place your kohlrabi stems and base into a perforated plastic bag in the crisper drawer of your refrigerator.
The leaves can be left on the stems or removed, but the stems and base will last longer if the leaves are removed. Lay your leaves from a spring or fall, and even winter crop on a long piece of paper towel and then carefully wrap it into a tube. Put the tube of leaves into its own plastic bag. Use your leaves within a few days for best freshness.
Stems and bases can be frozen for long-term storage. Wash your kohlrabi and remove the stems from the base. Peel the tough outer layer of skin off. If desired, cut your kohlrabi into ½” segments, although you can freeze it whole. Boil it in water (3 minutes for whole stems/bases, 1 minute for diced pieces) and then immediately transfer to cold water to stop cooking. Drain, pat dry, and lay kohlrabi on a baking sheet to freeze until solid, then transfer it into a freezer storage bag. Store kohlrabi in the freezer for up to 8 months.
Troubleshooting
While we’ve covered how to grow kohlrabi, there are a few issues you might encounter. Let’s go over how to handle problems that might arise while you’re growing kohlrabi in your garden.
Growing Problems
Woody bulbs can be caused by multiple issues: underwatering, age, or hot weather are the most common concerns. Make sure your plant has ample water, that it is not exposed to high temperatures for prolonged periods of time, and that you harvest when they’re still tender.
Pests
Cabbage aphids congregate on the underside of leaves and along the stems. These annoying pests prefer a sheltered location whenever possible to protect themselves while they’re feeding. A hard spray of water knocks them off the plant, and they won’t be able to get back on. For large outbreaks, neem oil or insecticidal soap is effective.
The beet armyworm is a larvae that can skeletonize leaves of your kohlrabi as well as other members of the cabbage family. To treat these before they devour your green leaves, apply a coating of Bacillus thuringiensis, which will gradually kill off the larvae.
Other caterpillars that might attack your kohlrabi include cabbage worms, cabbage loopers, and cutworms. All of these should also be treated with BT. Picking large caterpillars off the plant and dropping them into soapy water is a quick way to remove them.
Flea beetles eat a shothole pattern into leaves and can become a nuisance. Neem oil is effective for the home gardener, but a dusting of diatomaceous earth over the leaves can also work to reduce their numbers.
Kohlrabi Diseases
Alternaria leaf spot is a fungal disease that can cause brown or black spots on the foliage of infected plants. The lesions form rings and become brittle. It is caused by extended wet periods in colder months. Copper-based fungicides are effective against leaf spot.
Black rot is a bacterial disease that is more common in seedlings than established plants and is easily confused with fusarium. V-shaped lesions may appear on the foliage, turning the leaves brown and yellow until they collapse. Dark rings may also appear in the cross-section of the stem. Use healthy seeds, rotate the crop every two years, avoid sprinkler irrigation, and maintain good sanitation to avoid this problem.
Both downy mildew and powdery mildew are fairly common on the leaves of your kohlrabi. While these will not kill the plant in small amounts, large patches of diseased leaves can cause severe wilting and ruin the edible leaf surfaces. Applications of neem oil work as a preventative, and copper-based fungicides kill off any remaining spores on the plant.
Frequently Asked Questions
Q: Is kohlrabi easy to grow?
A: In cool weather conditions, kohlrabi is easy to grow. Warmer weather can cause problems, particularly if paired with humidity. Grow these plants in the cooler months of the year.
Q: Does kohlrabi transplant well?
A: Kohlrabi seedlings can be transplanted but do so very gently to avoid the risk of transplant shock.
Q: Is kohlrabi a perennial?
A: Technically speaking, kohlrabi is a biennial plant. For eating, these plants are grown as annuals and harvested during that first year.
Q: How long does it take to grow kohlrabi?
A: It takes roughly 55 days to grow kohlrabi.
Q: Will kohlrabi grow back after harvesting?
A: If you leave the bottom stem in the ground after you harvest, yes! It will grow back.
Q: Does kohlrabi need full sun?
A: At least 6 hours of full sun is needed to grow kohlrabi.
Q: What can you not plant next to kohlrabi?
A: Companion plant kohlrabi with beets, cucumber, and alliums.
Q: Why is my kohlrabi not forming bulbs?
A: This usually occurs when you space plants too closely or when temperatures aren’t suited for growing, and they’re either too hot or too cold. Sometimes improper watering is an issue.
