Kohlrabi

Kohlrabi is one of the fastest-growing brassicas and one of the most unusual-looking vegetables in the garden, forming a swollen, bulb-like stem just above the soil surface. It thrives in cool weather between 7-24°C (45-75°F) and matures in as little as 45-60 days, making it an excellent crop for spring and fall planting. Sow seeds directly 1 cm (1/2 inch) deep and 5 cm apart in rows spaced 30 cm apart, or start transplants indoors 4-6 weeks before the last frost for an earlier harvest.

Thin seedlings to 15-20 cm apart once they develop their first true leaves. Keep the soil consistently moist, as drought stress causes the bulb to become tough and woody. Mulch around plants to maintain even soil moisture and moderate soil temperature. Kohlrabi has relatively shallow roots, so avoid deep cultivation near the plants. A balanced fertilizer applied at planting provides adequate nutrition for this fast-growing crop.

For spring planting, sow as soon as soil can be worked — kohlrabi tolerates light frost. For fall crops, sow 6-8 weeks before the first expected frost. Fall-grown kohlrabi is often sweeter than spring crops due to cool maturation temperatures. Harvest when bulbs reach 5-8 cm (2-3 inches) in diameter for the most tender, crisp texture. Giant varieties like Superschmelz can grow to the size of a softball while remaining tender, but standard varieties become woody if left too long.

Kohlrabi's origins trace back to northern Europe, where it was developed through selective breeding of wild cabbage (Brassica oleracea) sometime in the late medieval period. Unlike its ancient brassica relatives — cabbage, kale, and broccoli, which have been cultivated for thousands of years — kohlrabi is a comparatively recent creation. The earliest reliable written descriptions come from the Italian botanist Mattioli in 1554, who noted it was already being grown in Germany and Italy. By the 1600s, kohlrabi had spread across Central and Northern Europe, particularly taking root in German-speaking regions where it became a kitchen staple.

The vegetable was brought to North America by European immigrants in the early 1800s, but it never achieved the widespread popularity it enjoys in its Central European heartland. Thomas Jefferson is recorded to have grown kohlrabi at Monticello, and it appeared in American seed catalogs throughout the 19th century. However, its unusual appearance — a swollen, above-ground stem studded with leaf stalks — may have limited its mainstream adoption compared to more familiar root vegetables like turnips and beets.

Today, kohlrabi remains most popular in Germany, Austria, Switzerland, and parts of Eastern Europe, where it is sold fresh in every market and used in a wide range of traditional dishes from creamy Kohlrabigemüse to hearty soups and salads. In India, particularly in Kashmir, a local variety called monj-hak has been cultivated for centuries and holds deep cultural significance in Kashmiri cuisine. Interest in kohlrabi has grown substantially in recent years among home gardeners and chefs worldwide, driven by its fast growth, mild flavor, versatility in the kitchen, and impressive nutritional profile.

Kohlrabi grows best in fertile, well-drained soil with a pH of 6.0-7.5. Work 5-8 cm of well-aged compost into the top 20 cm of soil before planting to provide both nutrients and moisture retention for the fast growth rate. Apply a balanced fertilizer (10-10-10) at planting at approximately 60 grams per square meter. Sandy soils benefit from extra compost to improve water-holding capacity, while heavy clay soils should be amended with compost and coarse sand or grown in raised beds to ensure adequate drainage.

Kohlrabi is a moderate feeder and generally does not need side-dressing given its fast 45-60 day maturity. Avoid excess nitrogen, which can cause the bulb to crack or develop hollow, pithy centers. Calcium is critically important for cell wall structure and bulb integrity — lime the soil if pH is below 6.0, and consider a calcium foliar spray during rapid bulb expansion if cracking has been a problem in past seasons. Boron deficiency, while uncommon, can cause brown, corky patches inside the bulb — a light application of borax (1 gram per square meter) at planting prevents this.

Kohlrabi benefits from consistent moisture more than heavy feeding, so prioritize mulching and irrigation over additional fertilization. Apply 5-8 cm of straw, shredded leaves, or grass clippings around plants once they are established to maintain even soil moisture and suppress weeds. If growth appears sluggish midseason, a light side-dressing of compost tea or dilute fish emulsion provides a gentle nutrient boost without the risk of excessive nitrogen. Avoid fresh manure, which can introduce weed seeds, burn shallow roots, and promote lush leaf growth at the expense of bulb development.

Harvest kohlrabi when the swollen stem reaches 5-8 cm (2-3 inches) in diameter — about the size of a tennis ball. Standard green and purple varieties become woody and fibrous if allowed to grow much larger, so check plants regularly once bulbs begin forming. Cut the stem at soil level with a sharp knife rather than pulling, which can disturb neighboring plants. The ideal harvest window is short for standard varieties — perhaps only 5-7 days between perfectly tender and unpleasantly woody — so daily monitoring is worthwhile once bulbs start sizing up.

The leaves are also edible and nutritious when young and tender — cook them like collard greens, add small ones to stir-fries, or blend into smoothies for a mild brassica boost. Harvest leaves selectively while the bulb is still developing, taking only one or two outer leaves at a time to avoid reducing the plant's photosynthetic capacity. Giant varieties like Superschmelz can be harvested at much larger sizes (up to 25 cm across) while retaining remarkably good texture, making them ideal for gardeners who prefer fewer, larger harvests.

For the crispest texture and mildest flavor, harvest in the morning after dew has dried but before the heat of the day. Fall-grown kohlrabi exposed to light frost actually develops a sweeter flavor as the plant converts starches to sugars in response to cold — a phenomenon shared with many brassicas. Succession plantings every 2-3 weeks extend the harvest window from a single concentrated picking to weeks of continuous supply. Pull or cut the entire plant at harvest rather than trying to leave the root in place, as kohlrabi does not resprout from the base.

Remove leaves immediately after harvest — they draw moisture from the bulb and accelerate wilting — and store them separately in a damp paper towel inside a plastic bag for up to 5 days. Whole, unwashed bulbs keep in a perforated plastic bag in the refrigerator crisper drawer for 2-3 weeks. For extended root cellar storage, layer unwashed bulbs in damp sand or peat moss at 0-2°C (32-35°F) and 90-95% humidity, where they can keep for 1-2 months while maintaining their crisp texture.

Kohlrabi freezes well for long-term preservation. Peel and dice bulbs into 1-2 cm cubes, blanch in boiling water for 2 minutes, immediately cool in ice water to halt cooking, drain thoroughly, and spread on a parchment-lined baking sheet to flash-freeze before transferring to labeled freezer bags. Frozen kohlrabi keeps for up to 10 months and works best in cooked dishes like soups, stews, and gratins — the crisp raw texture is lost after freezing, so plan accordingly.

Kohlrabi can also be lacto-fermented like sauerkraut for a tangy, probiotic-rich preserve that keeps for months in the refrigerator. Peel and shred or thinly slice the bulbs, toss with 2% salt by weight, pack tightly into a jar, and allow to ferment at room temperature for 5-7 days. Pickled kohlrabi in a vinegar brine with mustard seeds, dill, and garlic makes an excellent condiment. Dehydrating thin slices at 57°C (135°F) for 6-8 hours produces crispy kohlrabi chips that store in airtight containers for months — a healthy, addictive snack seasoned with sea salt or smoked paprika.

Kohlrabi is remarkably versatile and underappreciated in the kitchen. Raw, it has a crisp, juicy texture similar to a crisp apple or jicama with a mild brassica sweetness — peel and slice into sticks for crudites with hummus, grate into slaws with carrot and apple, or julienne for refreshing salads dressed with lemon vinaigrette. Children often enjoy raw kohlrabi sticks as a snack because of the mild, slightly sweet flavor and satisfying crunch. It substitutes beautifully for water chestnuts in stir-fries, maintaining its crunch even after brief cooking.

Roasting kohlrabi at high heat (220°C / 425°F) caramelizes the natural sugars beautifully — toss peeled wedges with olive oil, salt, and a pinch of smoked paprika for a simple, addictive side dish. Kohlrabi makes excellent creamy soups when peeled, cubed, simmered until tender, and pureed with a touch of cream and nutmeg. It can be mashed like turnips with butter and white pepper, or sliced thin and layered into gratins with cream and Gruyère cheese. Kohlrabi fries — cut into batons, tossed in oil and seasoning, and roasted until golden — are a lower-carb alternative to potato fries.

The young leaves are nutritious cooked as greens — sauté them with garlic and olive oil, or add to soups and stews in the last few minutes of cooking. In German and Central European cuisine, kohlrabi is traditionally served in a creamy white sauce (Kohlrabigemüse) as a comforting side dish. It pairs exceptionally well with cream, cheese, apple, caraway seeds, dill, lemon, mustard, and nutmeg. Pickled kohlrabi adds a crunchy, tangy element to grain bowls and sandwiches.