Kohlrabi Growing Guide
Kohlrabi is an unusual and versatile brassica that forms a swollen stem base, often called a bulb, which can be green, white, or purple externally with pale green or white flesh. It is best harvested young for its tender, crisp, and juicy texture, making it ideal for raw consumption in salads and coleslaws. It can also be lightly steamed, roasted, or sautéed. It has a sweet flavor, similar to broccoli or mild turnip, and its young leaves can be cooked like greens. Compared to many other brassicas, kohlrabi is fast growing.
This guidance applies to the crop in general. Individual varieties and local conditions can differ.
Planting information
Early sowings are best made indoors in a modular tray using peat-free seed compost, sowing two seeds per module at 1.5cm deep. Thin to one seedling per module, keeping them in good light and watering regularly. Seedlings are ready to plant out in 3-4 weeks when no more than 5cm tall. Outdoors, sow seeds from March to July (or August in mild autumns) when temperatures are above 10°C. Make a drill 1.5cm deep, water, sow seeds thinly, cover with soil, and firm gently. Space rows 30cm apart. Once seedlings are 2.5cm tall or have first true leaves, thin them to a final spacing of 15cm apart. Protect seedlings from slugs and snails. For containers, choose a pot at least 30cm wide and deep, fill with peat-free multi-purpose compost, water, scatter seeds thinly, and cover with 1.5cm of compost. Thin to 15cm apart. Young plants, whether indoor-sown or plug plants, should be planted outside when no more than 5cm tall, as larger plants may transplant less successfully. Ensure outside temperatures are consistently above 10°C to prevent bolting. Harden off plants for a couple of weeks gradually. Aim to plant out in mid- to late spring. Plant seedlings 15cm apart in rows 30cm apart.
Harvesting information
Harvest kohlrabi when young, typically between golf-ball and tennis-ball size, for optimal sweetness, mild flavor, and succulent, crunchy texture. Leaving them to grow too large can result in loss of flavor and tenderness, and they can turn woody, especially in hot, dry weather. With repeated sowings, harvesting can extend from May through to November, and potentially into December in milder areas. Protect crops with cloches or biodegradable fleece if harvesting into winter. To prepare, remove the outer skin, then grate or chop finely for salads and coleslaw, or lightly steam, sauté, or add to stews. Young leaves can be cooked like kale. Baby veg can be harvested in as little as six weeks, full size after about twelve weeks.