How to Grow Kohlrabi Kossak

Kohlrabi Kossak

Brassica oleracea var. gongylodes 'Kossak'

vegetable

Kohlrabi Kossak is a pale green cultivar of kohlrabi known for its large, uniform bulbs and excellent cold tolerance. This brassica produces tennis ball-sized swollen stems above ground that are tender and sweet when harvested at the right size. It's a cool-season crop prized for storage and market production.

Growing Conditions

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Sun: Full sun, 6-8 hours daily; partial shade in very hot climates

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Water: Consistently moist soil; 1-1.5 inches per week. Keep soil evenly moist to prevent splitting and ensure tender bulbs. Drought stress causes tough, woody texture.

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Spacing: 6-8 inches

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Days to maturity: 45-60

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Planting depth: 0.25 inches for seeds; transplants at soil line

Soil

Type: Well-draining fertile loamy soil rich in organic matter

pH: 6.0-7.5

Amendments:

Compost or well-rotted manure Balanced fertilizer (10-10-10) Lime if soil is too acidic (brassicas prefer slightly alkaline) Boron (trace amounts) to prevent hollow bulbs

Growing Zones

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Thrives in zones 3-8; can be grown spring and fall in cooler zones, or as winter crop in warmer zones

2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a

Growth Stages

Seedling

2-3 weeks

Tiny leaves with characteristic blue-green cast emerge from soil. First true leaves appear within 7-10 days.

Keep soil moist but not waterlogged. Provide bright light to prevent leggy growth. Thin seedlings to proper spacing early.

Vegetative Growth

3-4 weeks

Plant develops 4-6 true leaves and begins establishing root system. Leaf stems thicken slightly at base.

Maintain consistent moisture and apply balanced fertilizer every 2-3 weeks. Watch for cabbage worms and loopers; use netting if needed. Keep area weed-free.

Bulb Formation

2-3 weeks

Swollen stem begins to enlarge just above soil line, expanding into a smooth globe-shaped bulb. Leaves continue growing around the bulb.

Increase nitrogen slightly to support continued leaf growth, which feeds the bulb. Ensure consistent watering. Do not hill soil over bulb. Check size weekly starting at day 40.

Bulb Maturation

1-2 weeks

Bulb reaches harvestable size (3-4 inches diameter), remaining pale green and smooth. Skin becomes firm but bulb interior remains tender.

Harvest when bulbs are tennis ball-sized for best tenderness. Do not allow bulbs to over-mature (becomes woody and fibrous). Kossak stores well for extended harvest window.

Harvest & Storage

Ongoing through season

Mature bulbs are cut cleanly from plant. Leaves can be trimmed and composted or used as cooked greens.

Harvest in morning when plants are turgid. Kossak stores 2-4 months in cool (32-40°F), humid conditions. Remove outer leaves for longer storage.

Companion Planting

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Plant with:

Beets Carrots Onions Garlic Lettuce Spinach Dill Thyme Chamomile Marigolds

Avoid planting near:

Tomatoes Peppers Fennel Strawberries Beans Pole beans Cabbage family (within 12 inches) Broccoli (competing for similar nutrients)

Common Pests

Row covers on young plants; Bt (Bacillus thuringiensis) spray; hand-picking; companion planting with thyme and dill
Row covers until plants establish; neem oil spray; kaolin clay; reflective mulch; encourage natural predators
Bt spray; hand-picking; row covers; encourage parasitic wasps and birds
Strong water spray; insecticidal soap; neem oil; ladybugs and lacewing larvae
and
Beer traps; copper barriers; hand-picking at night; encourage ground beetles; diatomaceous earth
Row covers; lime dusting around base; crop rotation; parasitic nematodes in soil

Uses

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Tender roasted bulbs

Culinary

Young Kossak bulbs are delicious roasted whole or sliced, with a mild cabbage-like flavor that becomes sweet when caramelized. The tender interior makes it perfect for both raw slaws and cooked preparations. [source]

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Leafy green cooking

Culinary

The nutrient-dense leaves can be cooked like kale or collards when young and tender, offering an extra yield from each plant and reducing waste. [source]

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Glucosinolate and cancer prevention compounds

Medicinal

Like other brassicas, kohlrabi contains glucosinolates that convert to sulforaphane when chewed or cooked, compounds studied for potential anti-cancer and anti-inflammatory properties. [source]

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Long-term storage crop

Household

Kossak's excellent keeping quality makes it ideal for root cellar storage, winter eating, and extending the harvest season well into winter months without succession planting. [source]

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Pollinator garden support

Wildlife

If allowed to bolt, kohlrabi flowers attract bees, butterflies, and beneficial insects. The flowering stage also feeds late-season pollinators. [source]

This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.

Harvest Tips

Harvest Kossak bulbs when they reach 2-3 inches (tennis ball size) in diameter for peak tenderness; larger bulbs (up to 4 inches) are acceptable but may become slightly woody. Cut bulbs cleanly with a sharp knife 0.5 inches below the bulb. The longer you wait, the more fibrous the interior becomes. Kossak's excellent storage makes it ideal for extended harvesting—can leave some bulbs in ground in cool climates if mulched well, or harvest all and store at 32-40°F with 90%+ humidity for 8-12 weeks.

Fun Facts

🌱 The name 'kohlrabi' comes from German words 'kohl' (cabbage) and 'rabi' (turnip), though it is neither—it's an enlarged stem, not a root bulb like turnips.
🌱 Kohlrabi Kossak is particularly cold-hardy and was developed for reliable performance in Central European gardens; it can tolerate light frosts and actually tastes sweeter after a cold snap due to starch converting to sugars.
🌱 The entire plant is edible: the bulb, the leaves, the stems, and even the flowers, making it one of the most efficient vegetables for yield per square foot of garden space.

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