Hybrid

Kossak

Brassica oleracea var. gongylodes

Kossak is a hybrid brassica variety prized for its tender, sweet flavor and mild taste profile. This reliable variety reaches maturity in approximately 80 days, making it ideal for mid-season gardening. Known for its excellent eating quality, Kossak produces heads with a delicious, pleasant flavor that sets it apart from coarser cabbage varieties. It thrives in well-drained, fertile soil under full sun to partial shade conditions. Best suited for gardeners seeking an easy-to-grow brassica with superior culinary qualities and dependable performance.

Harvest

80d

Days to harvest

📅

Sun

Full sun to partial shade

☀️

Zones

6–9

USDA hardiness

🗺️

Height

10-24 inches

📏

Planting Timeline

Zone:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Start Indoors

Transplant

Direct Sow

Harvest

Start Indoors

Transplant

Direct Sow

Harvest

Showing dates for Kossak in USDA Zone 7

All Zone 7 brassica →

Zone Map

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Kossak · Zones 6–9

What grows well in Zone 7? →

Growing Details

Difficulty

Easy

Spacing8-10 inches

SoilWell-drained, fertile soil, slightly acidic to neutral

WaterRegular, consistent moisture

SeasonWarm season annual

FlavorSweet, tender, and delicious with a mild, pleasant flavor profile.

ColorWhite or pale cream

Size8"

Zone-by-Zone Planting Calendar

Zone	Indoor Start	Transplant	Direct Sow	Harvest
Zone 3	March – April	May – June	May – June	July – October
Zone 4	March – April	May – June	April – June	July – October
Zone 5	February – March	April – May	April – May	July – November
Zone 6	February – March	April – May	April – May	June – November
Zone 7	February – March	April – May	March – May	June – November
Zone 8	January – February	March – April	March – April	May – December
Zone 9	January – January	February – March	February – March	April – December
Zone 10	January – January	February – March	January – March	April – December
Zone 1	April – May	June – July	June – July	August – September
Zone 2	April – May	June – July	May – July	August – September
Zone 11	January – January	January – February	January – February	March – December
Zone 12	January – January	January – February	January – February	March – December
Zone 13	January – January	January – February	January – February	March – December

Succession Planting

Kossak runs about 80 days to harvest, which fits two plantings in most zone 6–9 gardens. Start seeds indoors in late February or early March, transplant out in April, and plan your first harvest for June. For a fall crop, count back 80 days from your first expected frost and start seeds accordingly — in zone 7 that lands around late July to early August, with harvest running September through November.

The main timing trap is heat. Bulbs that size up during consistently hot weather — daytime highs above 85°F — tend to turn pithy before they're worth cutting. If your transplant window falls in that range, wait it out. The fall planting almost always produces better texture than a late-spring run that hits summer before the bulbs fill out.

Complete Growing Guide

Harvest when round and about 8" diameter, before it begins to elongate. At this size, the roots will store well and the flesh will be sweet, tender, and delicious. Kossak will keep in cold storage for up to 4 months. Also available in organic seed. According to Johnny's Selected Seeds, Kossak is 80 days to maturity, annual, hybrid (f1).

Light: Full sun (6 or more hours of direct sunlight a day), Partial Shade (Direct sunlight only part of the day, 2-6 hours). Soil: Clay, Loam (Silt), Sand. Soil pH: Acid (<6.0), Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 0 ft. 10 in. - 2 ft. 0 in.. Spread: 1 ft. 0 in. - 2 ft. 0 in.. Spacing: 12 inches-3 feet. Growth rate: Medium. Maintenance: Medium. Propagation: Seed, Stem Cutting. Regions: Coastal, Mountains, Piedmont.

Harvesting

Kossak reaches harvest at 80 days from sowing per Johnny's Selected Seeds. Expect 8" at peak. As an annual, harvest continues until frost ends the season.

The fruits dry and split when ripe.

Color: Brown/Copper, Green. Type: Siliqua. Length: > 3 inches.

Garden value: Edible

Harvest time: Fall, Summer

Edibility: The foliage is edible raw or cooked but when cooked can emit an unpleasant odor.

Storage & Preservation

Kossak kohlrabi stores best in a cool, humid environment between 32–40°F with 90–95% relative humidity. Use perforated plastic bags or breathable containers in the crisper drawer; properly stored bulbs keep for 3–4 weeks. For longer preservation, blanch quarters for 3 minutes, then freeze in airtight containers for up to eight months. Fermentation works well too—slice thinly, salt at 2–3% by weight, and pack into jars under brine for tangy results in 2–3 weeks. Kossak's tender flesh also dries successfully; slice thin, dehydrate at 135°F until brittle, and store in airtight containers. Remove leaves before storage, as they draw moisture from the bulb and shorten shelf life significantly.

History & Origin

Kossak is an F1 hybrid developed through controlled cross-pollination. Listed in the Johnny's Selected Seeds catalog.

Origin: W. Europe

Advantages

+Harvests at perfect 8-inch size with naturally sweet and tender flesh
+Extended cold storage capability keeps roots fresh for up to four months
+Relatively quick 80-day maturity allows multiple plantings per growing season
+Easy difficulty level makes Kossak suitable for beginner gardeners

Considerations

-Requires precise harvest timing before elongation begins or quality declines
-Kohlrabi generally prefers cool weather and may bolt in excessive heat
-Needs consistently moist soil; drought stress causes tough, woody texture
-Limited market demand compared to common vegetables reduces commercial viability

Companion Plants

Onions and celery are the most useful neighbors here because their volatile sulfur compounds help mask the scent profile that draws cabbage moths (Pieris rapae) and flea beetles to brassicas. NC State Extension's IPM guidance is direct on this: interplanting unrelated crops dilutes the attractive odor of a preferred host, slowing pest movement across a planting and giving you more time to act. Marigolds get recommended constantly for brassicas — NC State acknowledges the repellent evidence is thin — but they do pull in generalist predators, and tucking a row between blocks of Kossak costs nothing. Lettuce and spinach fill the 8–10 inch gaps between plants without pulling water or nutrients away; they're gone before Kossak bulbs need the space.

Tomatoes and kohlrabi draw overlapping pest pressure, so putting them side by side just concentrates the problem in one part of the garden. Pole beans are a harder conflict — there's documented growth suppression between beans and brassicas, likely allelopathic — so keep them at least a full bed away. Strawberries compete aggressively for moisture and do nothing useful for Kossak in return.

Plant Together

Marigolds

Repels cabbage moths and other harmful insects with strong scent

Onions

Repels cabbage worms, aphids, and flea beetles with sulfur compounds

Lettuce

Benefits from shade provided by larger brassica leaves, efficient space use

Spinach

Grows well in partial shade of brassicas and doesn't compete for nutrients

Celery

Repels cabbage white butterflies and provides natural pest deterrent

Carrots

Loosens soil for brassica roots and doesn't compete for same nutrients

Dill

Attracts beneficial insects like parasitic wasps that control cabbage worms and aphids

Nasturtiums

Acts as trap crop for flea beetles and aphids, draws pests away from brassicas

Keep Apart

Strawberries

Competes for nutrients and can stunt brassica growth

Tomatoes

Inhibits brassica growth and both plants compete for similar nutrients

Pole beans

Can shade out brassicas and compete for nitrogen in soil

Nutrition Facts

Calories

31kcal(2%)

Protein

2.57g(5%)

Fiber

2.4g(9%)

Carbs

6.27g(2%)

Fat

0.34g(0%)

Vitamin C

91.3mg(101%)

Vitamin A

8mcg(1%)

Vitamin K

102mcg(85%)

Iron

0.69mg(4%)

Calcium

46mg(4%)

Potassium

303mg(6%)

Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #747447)

Pests & Disease Resistance

Common Pests

Cabbage moths, flea beetles, root maggots

Diseases

Clubroot, black rot, bacterial leaf spot

Troubleshooting Kossak

What you'll see, why it happens, and what to do about it.

Tiny round holes scattered across leaves, especially on young transplants in the first 2–3 weeks after setting out

Likely Causes

Flea beetles (Phyllotreta spp.) — adults overwinter in soil and leaf litter, emerge in spring and immediately target brassicas
Stressed or slow-establishing transplants, which are more vulnerable to feeding damage

What to Do

1.Cover transplants immediately with row cover (Agribon AG-19 or similar) and seal the edges — flea beetles find plants by smell, so physical exclusion is the most reliable fix
2.Remove the cover once plants are 8–10 inches tall and actively growing; healthy established kohlrabi outpaces minor feeding damage
3.Till under or remove crop debris after harvest to reduce overwintering sites in the bed

Plants wilt and collapse despite adequate soil moisture, with swollen, club-shaped roots when pulled

Likely Causes

Clubroot (Plasmodiophora brassicae) — a soil-borne pathogen that can persist for 15–20 years in infected ground
Planting brassicas — kohlrabi, cabbage, broccoli, collards — in the same bed more frequently than once every 3 years

What to Do

1.Pull and bag affected plants immediately — do not compost them
2.NC State Extension recommends keeping any one spot out of brassicas for at least 3 years; with clubroot already confirmed, stretch that to 4–5 years minimum
3.Lime the bed to raise soil pH to 7.2 or above before replanting — Plasmodiophora brassicae activity drops sharply in alkaline conditions

V-shaped yellow lesions starting at leaf edges, turning brown and papery, with darkened veins visible on the underside — typically shows up around day 30–40

Likely Causes

Black rot (Xanthomonas campestris pv. campestris) — a bacterial disease spread by infected seed, rain splash, and overhead irrigation
Watering late in the day so foliage stays wet overnight

What to Do

1.Strip and trash affected leaves; black rot moves fast through wet tissue and composting spreads it
2.Switch to drip or furrow irrigation to keep water off the foliage entirely
3.Next season, start with a confirmed disease-free seed lot or treat seed with hot water at 122°F for 25 minutes before sowing

Frequently Asked Questions

How long does Kossak brassica take to mature?▼

Kossak reaches maturity in approximately 80 days from planting. For best quality and storage potential, harvest when the roots are round and about 8 inches in diameter, before they begin to elongate. At this ideal size, the flesh will be sweetest and most tender.

Is Kossak a good variety for beginners?▼

Yes, Kossak is rated as easy to grow, making it excellent for beginner gardeners. This hybrid variety is forgiving and reliable. As long as you provide full sun to partial shade (4-6+ hours) and maintain consistent growing conditions, you should achieve good results even without extensive gardening experience.

How long can you store Kossak after harvest?▼

Kossak stores exceptionally well in cold storage conditions for up to 4 months. This extended storage life makes it an ideal variety for gardeners wanting to preserve their harvest through winter. Proper cool, humid storage conditions help maintain the quality and sweetness of the roots.

What does Kossak taste like?▼

When harvested at the recommended 8-inch diameter size, Kossak offers sweet, tender, and delicious roots. The flavor is mild and pleasant, making it versatile for various culinary applications. Harvesting at the proper size ensures optimal flavor development.

Can you grow Kossak in containers?▼

Yes, Kossak can be grown in containers, though it requires sufficient soil depth to accommodate the round root structure at maturity (about 8 inches diameter). Use a large container with well-draining soil, ensure 4-6+ hours of sunlight daily, and maintain consistent moisture for best results.