Often overlooked in the garden plot, purple kohlrabi is a strikingly beautiful and surprisingly versatile member of the cabbage family. Its unusual appearance, a swollen stem bulb that grows above the ground, belies a crisp, juicy texture and a mildly sweet flavor reminiscent of a broccoli stem with a hint of pepper. Growing this vibrant vegetable at home is a straightforward process that rewards the gardener with a unique and nutritious harvest. With proper planning and care, anyone can cultivate large, tender tubers that will become a highlight of their garden and kitchen.
Introduction to Purple Kohlrabi
A Unique Member of the Brassica Family
Kohlrabi, whose name is German for “cabbage turnip,” is not a root vegetable, despite its appearance. The edible, bulbous part is actually a swollen stem that develops just above the soil surface. This unique growth habit sets it apart from its cruciferous cousins like broccoli, cabbage, and cauliflower. Purple kohlrabi varieties offer the same crisp texture and flavor as their pale green counterparts but with an added visual flair. The vibrant purple skin is more than just decorative; it is rich in anthocyanins, powerful antioxidants also found in blueberries and red cabbage. The flesh inside remains a creamy white, creating a beautiful contrast when sliced.
Choosing the Right Purple Cultivar
While several purple varieties exist, they can differ in maturation time, size potential, and resistance to bolting. Selecting a cultivar suited to your climate and growing season is a foundational step for success. Some varieties are better for early spring plantings, while others excel in the cooler temperatures of fall. Researching specific traits will help ensure a bountiful harvest of tender, flavorful tubers.
| Cultivar Name | Days to Maturity | Average Tuber Size | Key Characteristics |
|---|---|---|---|
| Purple Vienna | 55-65 days | 5-7 cm | An heirloom classic, reliable and well-adapted. Best harvested small for tenderness. |
| Azur Star | 50-60 days | 7-10 cm | An early variety known for its deep purple color and resistance to becoming woody. |
| Kolibri F1 | 45-55 days | 10-12 cm | A hybrid with excellent vigor, uniform growth, and a crisp, sweet flavor. Holds well in the field. |
Understanding the fundamental characteristics of purple kohlrabi sets the stage for the next crucial phase: creating the perfect environment for it to grow. The quality of your harvest is directly tied to the groundwork laid before a single seed is even planted.
Soil Preparation and Planting
Creating the Ideal Foundation
Kohlrabi is a heavy feeder that thrives in fertile, well-drained soil. Success begins with proper soil preparation. The ideal soil pH is slightly acidic to neutral, ranging from 6.0 to 6.8. You can test your soil’s pH with a simple home kit. To enrich the soil, incorporate several inches of well-rotted compost or aged manure before planting. This not only provides essential nutrients but also improves soil structure and moisture retention, which is critically important for preventing the tubers from splitting or becoming woody. If your soil is heavy clay, amending it with sand or perlite can improve drainage.
Sowing Seeds for a Successful Start
You have two primary options for planting kohlrabi: starting seeds indoors or sowing them directly into the garden. The best method depends on your climate and desired harvest time.
- Indoor Start: For an early spring harvest, start seeds indoors 4 to 6 weeks before your last expected frost date. Plant seeds 1 cm deep in seed trays. Keep them moist and provide ample light. This head start allows you to transplant strong seedlings into the garden as soon as the soil is workable.
- Direct Sowing: For a spring crop, sow seeds directly in the garden 2 to 4 weeks before the last frost. For a fall crop, which often produces the highest quality tubers due to the cool weather, plant seeds in mid to late summer, about 6 to 8 weeks before the first fall frost.
Spacing for Optimal Growth
Proper spacing is non-negotiable for developing large, round tubers. Overcrowded plants will compete for resources, resulting in small, underdeveloped bulbs. When sowing seeds directly, plant them about 1.5 cm deep and 5 cm apart. Once the seedlings have developed two sets of true leaves, you must thin them. The final spacing should be at least 15 to 20 cm between plants. If you are transplanting indoor-grown seedlings, set them at this final spacing from the start. This gives each plant’s stem enough room to swell into a beautiful, robust tuber.
With your kohlrabi seedlings properly spaced in well-prepared soil, the focus now shifts to the ongoing attention they will need throughout the growing season to reach their full potential.
Plant Maintenance and Care
The Importance of Consistent Watering
The single most important aspect of kohlrabi care is consistent moisture. The swollen stem is composed primarily of water, and any interruption in its supply can have disastrous effects. Irregular watering, where the soil dries out completely and is then flooded, is a primary cause of splitting tubers. A dry spell can also signal the plant to stop growing, resulting in tough, woody flesh. Aim to provide about 2.5 to 4 cm of water per week, either from rainfall or irrigation. Using a soaker hose or drip irrigation is an excellent way to deliver water directly to the soil, keeping the foliage dry and reducing the risk of fungal diseases.
A Strategic Fertilization Plan
Kohlrabi benefits from a steady supply of nutrients to fuel its rapid growth. While the initial soil preparation provides a strong base, a mid-season boost can be beneficial. When the plants are about half-grown, you can side-dress them with a balanced, all-purpose fertilizer or a dose of rich compost. Be cautious not to over-apply nitrogen, as this can encourage excessive leaf growth at the expense of the tuber. The goal is a healthy balance that supports both foliage and stem development.
| Growth Stage | Fertilizer Type | Application Method |
|---|---|---|
| At Planting | Balanced (e.g., 10-10-10) or Compost | Incorporate into the top 15 cm of soil. |
| Mid-Season (4 weeks post-transplant) | Nitrogen-rich (e.g., Blood Meal) or Compost Tea | Side-dress around the base of the plant. |
Mulching for a Healthier Plant
Applying a 5 to 7 cm layer of organic mulch, such as straw, shredded leaves, or grass clippings, around your kohlrabi plants is a simple but highly effective practice. Mulch serves several key functions: it helps retain soil moisture by reducing evaporation, suppresses weed growth that would otherwise compete for water and nutrients, and moderates soil temperature, keeping the roots cool during warmer periods. As the organic mulch breaks down, it also adds valuable nutrients back into the soil.
Maintaining a healthy growing environment is the best defense against potential problems, but even the most well-tended garden can face challenges from pests and diseases.
Pest and Disease Management
Identifying and Controlling Common Pests
As a member of the cabbage family, kohlrabi is susceptible to a number of common garden pests. Early detection and intervention are key to preventing significant damage. One of the most effective preventative measures is the use of floating row covers, which create a physical barrier against flying insects from the moment you plant.
- Cabbage Worms: These green caterpillars are the larvae of the Cabbage White butterfly. They chew large, irregular holes in the leaves. They can be hand-picked off plants or controlled with an application of Bacillus thuringiensis (Bt), an organic pesticide.
- Flea Beetles: Tiny black insects that jump when disturbed, flea beetles chew numerous small “shot holes” in the leaves. They are most damaging to young seedlings. Row covers are the best defense.
- Aphids: These small, sap-sucking insects cluster on the undersides of leaves. A strong spray of water can dislodge them, or they can be treated with insecticidal soap.
Preventing Prevalent Diseases
Kohlrabi is generally a hardy plant, but it can be affected by fungal diseases, especially in damp or humid conditions. Prevention is far more effective than treatment. Good air circulation is essential, which is another reason why proper spacing is so important. Avoid overhead watering that leaves foliage wet for extended periods. The most serious disease to watch for is clubroot, a soil-borne fungus that causes roots to become swollen and distorted, stunting the plant’s growth. The only effective management for clubroot is a long crop rotation cycle, meaning you should not plant any Brassica family crops in the same spot for at least three to four years.
After carefully nurturing your plants and protecting them from harm, the rewarding final steps of the process are harvesting your crop and preparing it for the table.
Harvesting and Storage
The Perfect Time to Pick
The timing of your kohlrabi harvest is absolutely critical to its quality. Unlike many vegetables that can be left to grow larger, kohlrabi becomes tough, fibrous, and woody if it gets too big. The ideal time to harvest is when the swollen stem reaches a diameter of 5 to 8 cm, roughly the size of a tennis ball. Do not judge readiness by the size of the leaves, but by the size of the tuber itself. The flesh will be most tender and sweet at this stage. Check your plants frequently once they begin to swell, as they can grow quickly.
Techniques for a Clean Harvest
Harvesting kohlrabi is a simple and satisfying task. Using a sharp, clean knife or pruning shears, cut the stem at the soil line, just below the bulb. You can also pull the entire plant from the ground if the soil is loose, and then trim off the long taproot. Once harvested, you should immediately trim off the leaves, leaving about 2-3 cm of the leaf stems attached to the bulb. This is important because the leaves will continue to draw moisture from the tuber, causing it to soften and lose its crispness if left attached.
Storing Your Harvest for Future Use
Proper storage can extend the enjoyment of your kohlrabi crop for weeks or even months. For short-term storage, place the trimmed tubers in a plastic bag in the refrigerator’s crisper drawer, where they will keep for up to a month. For longer-term storage, kohlrabi can be kept in a cool, humid environment like a root cellar for several months. Ensure the temperature is just above freezing. Do not forget the leaves; they are entirely edible and nutritious, similar to kale or collard greens. Store the leaves separately in a plastic bag in the refrigerator and use them within a few days.
With a successful harvest safely stored, the final joy comes from exploring the many culinary uses for this unique and delicious vegetable.
Recipe Ideas for Purple Kohlrabi
The Crisp Appeal of Raw Kohlrabi
One of the best ways to appreciate the subtle sweetness and fantastic crunch of kohlrabi is to eat it raw. Its texture is often compared to that of a crisp apple or jicama. Before using, you must peel away the tough outer skin, both the purple layer and the fibrous white layer just beneath it, until you reach the tender, translucent flesh. Once peeled, the possibilities are endless.
- Simple Slices: Cut the kohlrabi into thin sticks or rounds and serve with your favorite dip, such as hummus or a creamy herb dressing. This is a refreshing and healthy snack.
- Vibrant Slaws: Grate or julienne the kohlrabi and toss it with shredded carrots, red cabbage, and a light vinaigrette for a colorful and crunchy slaw that is a perfect side dish for grilled meats.
- Salad Additions: Dice the peeled kohlrabi and add it to green salads or grain bowls for an unexpected burst of crisp texture.
Exploring Cooked Preparations
Cooking kohlrabi transforms its flavor, making it milder and more tender while retaining a pleasant bite. It is incredibly versatile and can be substituted for potatoes, turnips, or broccoli stems in many recipes. Roasting is a particularly popular method, as it caramelizes the natural sugars and brings out a deep, nutty sweetness. To roast, simply peel and chop the kohlrabi, toss with olive oil and seasonings, and cook in a hot oven until tender and golden brown. It can also be steamed, boiled and mashed, puréed into a creamy soup, or sliced thinly and fried into chips.
Don’t Forget the Greens
It is a common mistake to discard the kohlrabi leaves, but they are a delicious and nutritious bonus harvest. They taste similar to collard greens or kale and are packed with vitamins. Prepare them as you would any other cooking green: remove the tough central stem, chop the leaves, and then sauté them with garlic and olive oil, steam them until tender, or add them to soups and stews for the last few minutes of cooking. Using both the tuber and the leaves ensures that nothing from your hard work goes to waste.
Growing purple kohlrabi is a rewarding journey from seed to plate. By choosing a suitable variety, diligently preparing the soil, and providing consistent care regarding water and nutrients, any gardener can succeed. Vigilance against pests and harvesting the tubers at their peak tenderness are the final keys to a perfect crop. This unique vegetable not only adds a splash of vibrant color to the garden but also offers a versatile, crisp, and delicious ingredient for countless healthy meals.
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