Kohlrabi

Growing Conditions

Growing Zones

Thrives in USDA Zones 3 - 9

Companion Planting

When to Plant

• Start Indoors

  4–6 weeks before last frost date

• Transplant

  2–4 weeks before last frost date in spring; 6–8 weeks before first fall frost

• Direct Sow

  2–4 weeks before last frost date; or late summer for fall crop

• Harvest

  Cut bulbs at soil level when 2–3 inches in diameter; larger bulbs become woody and fibrous

Organic Growing Tips

• Side-dress with compost or worm castings when bulbs begin to swell to fuel rapid sizing without excess nitrogen that promotes leaves over bulb

• Mulch with straw or shredded leaves to retain soil moisture and keep roots cool; inconsistent watering causes cracked, pithy bulbs

• Apply diluted compost tea every 2–3 weeks to support steady, even growth and strengthen resistance to aphids and cabbage worms

• Use floating row cover from transplant to harvest to exclude cabbage moths, imported cabbageworms, and flea beetles without any sprays

• Rotate kohlrabi with non-brassica crops on a 3–4 year cycle to reduce clubroot and other soil-borne brassica diseases

• Interplant with onions or nasturtiums as a companion planting strategy shown in traditional kitchen gardens to deter aphids and whiteflies

Common Pests

• Cabbage worms
• Imported cabbageworm
• Flea beetles
• Aphids
• Cabbage loopers
• Slugs
• Harlequin bugs

Taxonomy

Kingdom

Plantae

Family

Mustard family (Brassicaceae)

Genus

Brassica

Species

Brassica oleracea var. gongylodes

Natural History

Kohlrabi is one of the many cultivated varieties of Brassica oleracea, the same highly plastic species that gave rise to cabbage, broccoli, cauliflower, and kale through centuries of selective cultivation in Mediterranean Europe. The swollen stem that defines kohlrabi is thought to have been developed in northern European gardens by the fifteenth or sixteenth century; the botanist Matthioli described it in 1554, and it spread rapidly through German, Austrian, and Bohemian kitchen gardens. The name derives from the German Kohl (cabbage) and Rabi (turnip). Unlike turnip, the edible bulb forms above ground, making it easier to harvest in wet or clay soils where root crops struggle.

Traditional Use

Kohlrabi has not figured prominently in formal medicinal traditions and is documented primarily as a food plant. European herbalists from the sixteenth century onward noted it mainly in the context of kitchen cultivation rather than therapeutics. Historical interest in the brassica family more broadly centered on cabbage leaves and seeds rather than kohlrabi specifically.

• Early modern European herbalism, 16th century - bulb

  Matthioli's 1554 herbal described kohlrabi as a garden curiosity eaten cooked or raw by Italian and German populations, noting it was thought to be nourishing and easy to digest compared to heavier root vegetables.

• Central European folk tradition, 17th–19th century - leaves and bulb

  In German and Bohemian households, kohlrabi leaves were used alongside the bulb in simple broths prepared for convalescents, reflecting a broader European pattern of associating cooked brassica vegetables with mild, restorative eating during illness.

Kohlrabi is safe for most people as a food plant. Individuals on anticoagulant medications should be aware that brassica vegetables contain vitamin K. Those with thyroid conditions sensitive to raw goitrogenic foods may wish to consult a physician about large quantities of raw brassicas.

This information is provided for historical and educational purposes only and is not medical advice. Always consult a qualified healthcare professional before making decisions related to your health.

Morphology (Plant Structure & Identification)

• Root System

  Shallow fibrous roots spread close to the soil surface, making kohlrabi sensitive to cultivation or hoeing near the plant base; keep the area mulched rather than cultivated to avoid root disturbance.

• Stem

  The edible part is a greatly swollen, globe-shaped stem internode that forms just above the soil surface; leaf scars left as outer leaves are removed make the bulb look knobby and are completely normal.

• Leaves

  Blue-green to purple leaves emerge from the top of the swollen bulb on long petioles; yellowing lower leaves are a sign of nitrogen stress or overcrowding, while powdery or mottled leaves suggest fungal infection or aphid damage.

• Flowers

  If allowed to bolt under heat or long days, kohlrabi sends up a tall flower stalk with small yellow brassica-type flowers; bolted bulbs become woody and inedible, so remove plants that send up flower stalks.

• Fruit

  The primary edible structure is the stem bulb, harvested before it exceeds 3 inches in diameter; seed pods resemble small slender siliques typical of brassicas and can be saved from isolated, open-pollinated plants for seed propagation.

Known Varieties

Common cultivars worth knowing

• Early White Vienna

  A classic open-pollinated pale green variety that matures in about 55 days with a mild, tender bulb; one of the most widely grown heirloom kohlrabis in home gardens.

  Best for: Spring and fall crops, seed saving, all-purpose kitchen use

• Early Purple Vienna

  Identical in flavor and texture to White Vienna but with striking purple skin; the flesh inside remains white and the purple color deepens in cool weather, making it visually distinctive at market.

  Best for: Ornamental kitchen gardens, fall crops, fresh eating

• Kolibri

  A reliable F1 hybrid purple kohlrabi that matures quickly around 45 days, holds its tenderness at larger sizes than heirloom types, and resists bolting better than open-pollinated varieties.

  Best for: Short-season gardens, succession planting, reliability in variable spring weather

• Superschmelz

  A giant heirloom variety that can grow to 8–10 inches in diameter while remaining sweet and tender, unlike standard varieties that become pithy when oversized; particularly popular in German-speaking Europe.

  Best for: Long-season growing, storage, feeding a family from a small number of plants