Kohlrabi is a flowering plant and 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. However, today this odd-looking plant is found worldwide. It is cultivated as a food source and is rich in vitamin C and vitamin B. It is 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 and 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, although its skin is a bit tough and is generally removed. It can be consumed raw or used in salads, soups, or meat-based dishes.
This alien, bizarre vegetable may not resemble anything else we usually eat, but that’s part of its charm. Whether white, purple, or green in color, it will definitely be an unusual addition to your garden beds… and a delicious one, too. So let’s talk about how to grow kohlrabi so that you can enjoy this unusual 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, 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. 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, ranging from su hào in northern Japan to kedluben in the Czech Republic. But while the names are unusual, so is the plant itself!
Wondering “what does a kohlrabi look like?” If so, then you’ve come to the right place. Kohlrabi has a broad, roundish bulb with stems that protrude from it. These stems can reach anywhere from 6 to 18 inches in height, depending on the variety. Big, cabbage-like leaves with long petioles and wavy edges top each stem. The plant also produces flowers that are generally white or yellow. The flowers bloom in clusters on top of the flowering stalks.
As is to be expected, this alien-looking garden plant is harvested for food. Kohlrabi is not a root vegetable, as all portions are edible, but the bulb is most commonly used culinarily. While the vegetable is enjoyed all around the world, 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 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.
Trying to determine how to grow kohlrabi the best way? The first step is planning the best start for the plant. After all, it won’t grow well if it’s in the wrong location or planted 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’ll be starting them indoors. These vegetables take 45 to 60 days to mature. As kohlrabi can survive an early frost, warm-climate dwellers can sow seeds in the late summer or early fall for a crop in the cool weather of autumn. Warm locations like southern California can grow kohlrabi all winter long!
Sow seeds directly in the ground or start them indoors for transplants. 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 for your 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.
Traditional spacing for growing kohlrabi is 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 can really increase the quantity you’re able to plant.
But now that we’ve discussed spacing kohlrabi, how to plant is essential to cover as well. For sowing kohlrabi seeds, plant ¼” deep with just a light dusting of soil overtop. Once they’ve germinated, thin to your preferred spacing 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, you can put them out into the garden once they’ve been hardened off. Plant at the same depth they were in their pot. Avoid even allowing an inch deep of soil to build up around the bulbous 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.
So now we’ve covered planting, and you’ll be asking how to grow kohlrabi for the best results. Let’s talk about elements like your garden soil and other important factors for good growth!
Sun and Temperature
These plants require 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 bulb turn woody. Make sure that the temperature is not higher than 75°F (23.9°C) during the harvesting season for the peak flavor. Kohlrabi can be grown in USDA growing zones 3 to 10.
Watering and Humidity
When considering how to grow kohlrabi, remember these plants need quite a bit of moisture to supply those bulbs, stems, and leaves. Keep the soil 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.
An inch of water per week is recommended, but if the weather’s rainy, you can skip watering as nature will handle it.
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 for added nutrition and water absorption. 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 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 the 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 growing kohlrabi in containers, regular fertilization is a must as they will drain the soil of nutrients regularly. However, they have shallow but large root systems, so apply your fertilizer in a ring around the plant so that it does not 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 will retain the dissolved nutrients. If you have ample supplies of organic matter in the soil, regular applications of liquid fertilizer will work.
Pruning is not necessary when growing kohlrabi except for harvesting purposes.
Kohlrabi is typically propagated through seeds only. Other methods of propagation just 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 for food. Growing kohlrabi can be a lot of fun, but so is harvesting kohlrabi plants for future meals!
While we’ve covered how to grow kohlrabi, harvesting can be a bit tricky by comparison as it relies on what you plan on using of the plants. Each portion has a slightly different harvesting time based on what use it will be put to.
For the leaves and stems, you have the option of cut and come again growing methods. Harvest 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.
Individual leaves can be snipped 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 it. Waiting for it to grow larger is not always better as more mature kohlrabi bulbs tend to become woody with age. We recommend a good median size of about 3 inches To harvest this base, remove the entire plant from the soil and then cut off the root ends. Clip off leaves and stems flush with the bulb at the time of harvest.
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). Since few of us can match those exact conditions, 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 themselves can be left on the stems or removed, but the stems and base will last longer if the leaves are removed. Lay your leaves 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. To do this, 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 it can be frozen whole as well. Blanch in boiling 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 on a baking sheet to freeze until solid, then transfer into a freezer storage bag.
While we’ve covered how to grow kohlrabi, there are still a few growing issues you might encounter. Let’s go over how to handle any problems that might arise while you’re growing kohlrabi in your garden.
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 this cool weather plant is not exposed to high temperatures for prolonged periods of time, and that you harvest when they’re still tender.
Cabbage aphids will 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 will knock them off the plant and they won’t be able to get back on without assistance. 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. While there are some commercial-grade pesticides that are also effective, BT is usually the best option for the home garden.
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 obvious worms when discovered.
Flea beetles will 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.
Alternaria leaf spot is a fungal disease that can cause brown or black spots on the foliage. The lesions often form rings and become brittle. It is caused by extended wet periods in colder months. Copper-based fungicides are effective against this leaf spot.
Black rot is a bacterial disease that is more common in seedlings as compared to 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 plants. While these will not generally kill off 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 will 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. Try to 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. Try not to damage the roots to avoid the risk of transplant shock.
Q: Is kohlrabi a perennial?
A: Technically speaking, kohlrabi is a biennial plant. For the purposes of eating, these plants are usually grown as annuals and harvested during that first year.
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