Le kohlrabi, or kohlrabi, is a vegetable plant prized for its crisp and flavorful bulbs. Growing it allows for regular harvests while enriching the garden. Varieties such as brassica oleracea there. gonglodes These varieties offer rapid growth and adapt well to rich, well-drained soils. Sowing, planting, and maintenance require care and attention to prevent diseases and pests. Harvesting and storage are straightforward if the appropriate techniques are followed. This practical guide details all the steps, from variety selection to post-harvest care, to ensure successful cultivation.
Table of contents
Choosing the variety of kohlrabi
Varieties suitable for cultivation in France
Several varieties of kohlrabi are well-suited to the French climate. Among the most widely cultivated are the Austrian white, prized for its rapid growth and cold hardiness, and the Munich violet, which develops firm, colorful bulbs. The Alsatian sweet is ideal for late harvests thanks to its good storage qualities. Some varieties originating from brassica oleracea there. gonglodes They are also selected for their natural resistance to common diseases and their adaptability to heavy or clay soils.
Selection criteria
Choosing a variety requires considering several key criteria. The growing season generally varies between 45 and 90 days depending on the cultivar, influencing the optimal harvest time. Cold tolerance is crucial for spring and autumn crops, while disease resistance reduces the need for treatments. It is also important to consider the size and firmness of the bulbs, which must suit storage and consumption requirements.
Local and hybrid varieties
Local varieties often retain a traditional taste and good hardiness, while modern hybrids offer more uniform growth and better pest resistance. Hybrids derived from brassica oleracea These varieties can be particularly beneficial for gardens where the soil is prone to fungal diseases. Depending on the growing area, some varieties are recommended for early sowing, others for winter harvesting, thus extending the period of vegetable availability.
Where to plant kohlrabi
Ideal exhibition conditions
Kohlrabi prefers full sun to thrive. An area receiving at least six hours of direct sunlight per day is recommended. However, in very hot climates, light afternoon shade can help prevent excessive heat stress. Avoid shady or overly humid locations, as these slow growth and promote disease.
Suitable soil type
Kohlrabi grows best in fertile, well-drained, and light soil. Loamy or sandy-loamy soil, rich in organic matter, is ideal. It should be deep enough to allow the bulb to develop. The optimal pH is between 6,0 and 7,5. Soil that is too acidic or too alkaline can limit the absorption of essential nutrients.
Amendments and fertilization before planting
Before sowing or planting, it is advisable to work the soil deeply (20 to 30 cm) to aerate it and facilitate root growth. Adding well-rotted compost or mature manure improves soil structure and provides essential nutrients. In addition, a balanced fertilizer (nitrogen, phosphorus, potassium) can be incorporated to ensure a good start. However, avoid excess nitrogen, which promotes abundant foliage to the detriment of the bulb.
Crop rotation and associations
To limit the risk of disease and soil depletion, it is important not to grow kohlrabi in the same spot two years in a row. Rotating with unrelated plants, such as... legumes, helps maintain fertility. Also avoid planting members of the Brassicaceae family (cabbages, radishes, turnips) nearby, as they often attract the same pests and diseases.
Sowing and planting kohlrabi
Sowing period
Kohlrabi is generally sown in spring, as soon as the soil temperature reaches approximately 10°C (50°F). In temperate climates, this often corresponds to late March or early April. It is also possible to sow in autumn, between August and September, for a harvest at the end of the year, provided the ground is not frozen. In a greenhouse, sowing can begin slightly earlier for a more rapid start.
Sowing technique
Sowing can be done directly in the ground or in pots for later transplanting. Direct sowing requires well-prepared, light soil. Seeds should be sown at a depth of about 1 to 2 cm, in rows spaced 30 cm apart, then thin out the plants once they have a few leaves to keep the most vigorous ones, respecting a spacing of 15 to 20 cm between each plant. Sowing in pots allows better control of growing conditions, especially in regions with cool springs, before transplanting into the ground when the plants have reached a height of 8 to 10 cm.
Spacing between plants
To ensure proper bulb development, it is important not to crowd the plants. A spacing of 20 to 25 cm between each plant and 30 to 40 cm between rows is recommended. This also facilitates air circulation, reducing the risk of disease.
Transplanting
If sowing was done in pots, transplanting into the ground should be done when the plants have between 3 and 5 true leaves, generally 3 to 4 weeks after sowing. Care must be taken to water well after planting to limit water stress. Transplanting should preferably be done in the late afternoon or on a cloudy day to avoid too much shock to the young plants.
Watering and fertilizing kohlrabi
Frequency and quantity of water
Kohlrabi requires regular watering to ensure healthy bulb growth. The soil should be kept moist, but never soggy, as excess water can cause root rot. During dry periods, a deep watering once or twice a week is ideal. In cooler or wetter weather, reduce the frequency. It is best to water early in the morning or late in the day to minimize evaporation.
Watering Methods
Drip irrigation is particularly well-suited to kohlrabi because it delivers water directly to the roots while limiting moisture on the foliage, thus reducing the risk of disease. Alternatively, watering by hand at the base of the plant also works. Avoid overhead watering, which can encourage the growth of fungi on the leaves.
Additional fertilization during cultivation
Kohlrabi benefits from an additional application of nitrogen approximately 3 to 4 weeks after planting to support foliage and bulb growth. Use a balanced fertilizer or an organic fertilizer rich in nitrogen, respecting the recommended dosages to avoid root burn. Additionally, a potassium supplement promotes bulb development and improves disease resistance. Fertilization can be repeated once at mid-crop, depending on the plants' growth stage.
Routine kohlrabi maintenance
Hoeing and weeding
Kohlrabi requires clean soil around its base to avoid competition with weeds such as... thistleswhich draw water and nutrients. Regular hoeing is recommended, especially at the beginning of the growing season, to aerate the soil and facilitate water absorption. Manual weeding is preferable to avoid damaging the shallow roots.
mulching
Mulching around plants is an excellent way to retain soil moisture, limit weed growth, and protect the soil from temperature fluctuations. Use organic materials such as straw, dead leaves, or compost. Mulching also reduces the risk of soil being sprayed onto the leaves during watering or rainfall, which reduces the risk of disease.
tutoring
Kohlrabi is a low-growing, sturdy plant that generally doesn't need staking. However, if you're growing a particularly tall variety or if your area experiences strong winds, a lightweight stake can help keep the plant upright and prevent the bulb from touching the ground.
Prevention and management of diseases and pests
Main diseases of kohlrabi
Kohlrabi can be affected by several common diseases, including mildew, which manifests itself as yellowish spots on the leaves followed by powdery white spots on the underside, and root rot, often linked to excess humidity. Powdery mildew can also appear in hot and humid conditions, forming a white veil on the leaves. Finally, the cabbage clubroot may cause abnormal root development.
Prevention through good cultural practices
Crop rotation is essential to limit the persistence of pathogens in the soil. Avoid planting kohlrabi or other brassicas in the same spot more than once every three years. Maintaining good spacing between plants promotes air circulation and reduces humidity, thus slowing the spread of fungal diseases. Mulching also helps limit the splashing of contaminated soil onto the leaves.
Biological control and natural treatments
Use plant purines (nettle, horsetail) sprayed to strengthen the natural resistance of plants and limit attacks. In the event of an infestation, use organic insecticides based on Bacillus thuringiensis or black soap to control pests without harming the environment. Rapid removal of diseased leaves reduces the source of infection.
Managing Common Pests
Aphids are common on kohlrabi, weakening the plants. They can be repelled or eliminated by spraying with water, introducing ladybugs, or using insecticidal soap. Slugs and snails often attack young plants; install natural barriers such as wood ash or crushed eggshells, or collect them by hand in the evening. Flea beetles, small jumping beetles, can cause perforations in the leaves, and control involves destroying crop residue and using insect netting.
Kohlrabi harvest
Signs of kohlrabi maturity
Kohlrabi is ready to harvest when the bulb reaches a diameter of 5 to 8 centimeters, usually between 8 and 12 weeks after sowing. The bulb should be firm to the touch and perfectly round. It is important not to leave kohlrabi in the ground for too long once mature, as it can become fibrous and tough.
Harvesting techniques
To harvest, grasp the bulb at the base of the plant and gently pull, gently lifting the soil around it to avoid damaging the bulb. Use a garden fork if the soil is compact. Then cut the leaves with a clean knife, leaving a small stem of about 2 cm. Remove any damaged or yellowed leaves to avoid exhausting the plant if you want to let it produce more.
Tips for successfully growing kohlrabi
Recommended varieties
Some varieties of kohlrabi are better suited to different seasons and climatic conditions. For example, early varieties like 'Vienna White' are suitable for spring sowing, while more hardy varieties such as 'Kossack' are more resistant to cold and are ideal for autumn sowing. Choosing a suitable variety makes growing and harvesting easier.
Managing extreme temperatures
Kohlrabi tolerates cool temperatures well, but prolonged frosts can damage the bulbs. If frost is expected, protect the plants with horticultural fleece or a thick layer of mulch. Conversely, during periods of intense heat, regular watering and mulching help retain soil moisture and reduce water stress.
Multiple harvests in the season
To prolong production, staggered sowing every two to three weeks is recommended, especially in spring and summer. This allows for staggered harvests and avoids simultaneous overabundance. Late sowing in a greenhouse can also provide a final harvest before winter.
Post-harvest maintenance of kohlrabi
Cleaning and sorting
After harvesting, kohlrabi bulbs must be carefully cleaned to remove soil and plant debris. Damaged or yellowed leaves should be removed to limit the growth of mold and bacteria. Careful sorting also allows for the separation of damaged bulbs from the healthy ones, ensuring better preservation.
Washing and drying
Washing with clean water is recommended to remove any residual dirt, without immersing the bulbs for too long to prevent excess moisture. After washing, the bulbs should be air-dried in a shaded and well-ventilated area, which reduces the risk of rot during prolonged storage.
Storage and preservation
Kohlrabi keeps best in a cool, humid environment, ideally between 0 and 4°C with a relative humidity of 90%. The bulbs can be placed in ventilated crates or perforated bags to prevent condensation. Regular inspection is necessary to remove any bulbs that are beginning to deteriorate in order to preserve the rest of the harvest.
Conclusion
Growing kohlrabi requires careful attention at every stage, from choosing the right variety to post-harvest care. Well-prepared soil, suitable sun exposure, and regular monitoring help prevent diseases and pests while ensuring optimal bulb development. Harvesting at the right time and proper storage extend shelf life and preserve the quality of the vegetable. By following these principles, even novice gardeners can grow firm and flavorful kohlrabi. Regularity and careful observation of the garden remain the keys to successful cultivation.
FAQ
How to sow kohlrabi correctly?
Sowing is usually done in seed trays or pots indoors or under cover. The seeds should be planted 1 cm deep in a light, moist substrate. Once the seedlings are strong, they can be transplanted outdoors, ensuring sufficient spacing.
When to plant kohlrabi in the garden?
Planting takes place in spring or late summer, depending on the variety. The soil should be well-worked and enriched with compost to encourage bulb formation. Moderate temperatures promote steady development and prevent heat stress.
How to protect kohlrabi from diseases?
Crop rotation is essential to limit fungal diseases. It is advisable to choose resistant varieties derived from brassica oleracea and to maintain good ventilation between the plants. In case of infections, biological treatments can be applied without harming the environment.
What are the pests of kohlrabi and how can they be managed?
Aphids, flea beetles, and caterpillars can damage leaves and stunt growth. Using traps, physical barriers, and natural predators can limit their impact. Regular plant inspections facilitate early detection and effective pest management.
How to store kohlrabi after harvesting?
The bulbs must be sorted and cleaned to remove damaged leaves and soil. They should be stored in a cool, humid place, ideally between 0 and 4°C. Frequent inspection is necessary to remove any deteriorating bulbs and prolong their shelf life.
