Kossak is a giant storage kohlrabi bred for serious harvests. This F1 hybrid reaches maturity in 80 days from transplants, producing impressively large bulbs that store exceptionally well, making it the choice for gardeners planning to preserve their crop through winter. Unlike smaller varieties harvested at 2-3 inches, Kossak can grow to 8 inches in diameter without becoming woody or tough, a rare trait that comes from careful breeding. The mild, cool-season preference means it thrives in spring and fall gardens across most climates, or as a winter crop in warmer regions.
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Kossak stands apart as a storage-focused kohlrabi that achieves massive size without sacrificing tenderness, a combination many gardeners chase but few varieties deliver. The F1 hybrid vigor gives you reliable, uniform bulbs perfect for succession planting or a single large harvest. At 10 inches between plants, it needs more space than typical kohlrabi, but that spacing is the secret to growing those impressive 8-inch storage bulbs that stay crisp and sweet for months.
Kossak is grown specifically for storage and extended use rather than fresh-from-the-garden eating. The large bulbs are roasted until caramelized, revealing a mild, sweet flavor that deepens with cooking. They're also sliced thin and sautéed, boiled in soups where their size makes them practical to peel and cut, or fermented for preservation. The stem and leaves are equally edible, though this variety is primarily bred for the bulb itself.
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Start seeds indoors 4-6 weeks before transplanting. Sow at 65-75°F, spacing 3-4 seeds per inch in open flats or 2 seeds per cell in cell flats, then thin to 1 seedling per cell. This timing ensures strong transplants ready to go out when conditions are cool.
Transplant seedlings outdoors 10 inches apart once they have developed true leaves and soil has warmed to a suitable temperature for kohlrabi growth. Harden off gradually over several days to prevent transplant shock. Transplanting into cool soil (spring) or during late summer heat decline (fall crop) gives best results.
Harvest Kossak when bulbs reach 8 inches in diameter for storage, rather than the smaller 2-3 inch size typical of eating varieties. At this size, the bulbs remain tender and sweet, not woody. Check bulb diameter by gently uncovering soil around the base to gauge size without pulling the whole plant. Harvest before heavy frosts if you intend to store indoors, or leave in the ground in mild climates where they can overwinter naturally.
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