How to grow kohlrabi

Fancy growing something unusual that isn’t widely available in supermarkets? Then this odd-looking but tasty and versatile brassica is a good choice. Kohlrabi forms a swollen stem base, often called a bulb, which can be green, white or purple on the outside, with pale green or white flesh inside. It’s best harvested young, when tender, crisp and juicy, ideal for eating raw in salads and coleslaws. It can also be lightly steamed, roasted or sautéed. It has a sweet flavour, like broccoli or mild turnip, to which it’s closely related. The young leaves can also be cooked like greens. 

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Often said to resemble a Sputnik, kohlrabi is an unusual-looking yet tasty crop

Purple varieties are best for late-summer sowings, for harvesting in autumn or even winter

For varieties that performed particularly well in RHS growing trials, see our list of AGM fruit and veg (135kB pdf) and our Recommended Varieties, below. You can also see many crops, including kohlrabi and other brassicas, in the veg plots at the RHS gardens, so do visit to explore how they’re grown, compare the varieties and pick up useful tips and inspiration. 

Kohlrabi grows best in a sunny site with fertile, moisture-retentive soil. It doesn't need as much nitrogen as many other brassicas, and will grow in light, sandy soil, as well as heavy soil. Some varieties will also grow in partial shade, especially in summer. If your soil has a pH level below 6, consider applying lime to raise the pH and help deter club root disease – you can carry out a simple pH test to check if this is necessary. Kohlrabi is a brassica, so it should be grown with its other cabbage relatives in crop rotations.

Weed the soil thoroughly, then add lots of garden compost – about two bucketfuls per square metre/yard – to improve moisture retention. Firm the ground well, then rake to remove lumps and stones. Alternatively, if you're practicing no-dig, mulch the soil with organic matter ahead of sowing or planting directly into the mulch.

Early sowings are best made indoors, as cold temperatures can cause plants to bolt (flower prematurely), meaning the bulb won’t swell. Kohlrabi is easy to sow outdoors in spring and summer – spring sowings tend to grow more quickly, while late-summer sowings provide a crop in autumn and even into early winter.  Purple varieties tend to be hardier, so are a good choice for late-summer sowings. If you sow several small batches at regular intervals, you can extend your harvest across multiple seasons.

Young kohlrabi plants, either grown from seed indoors or bought as plug plants, should be planted outside when no more than 5cm (2in) tall – if larger, they may transplant less successfully. Make sure the temperature outside is consistently above 10°C (50°F), as cooler conditions can lead to bolting (premature flowering).

Prepare them for life outdoors by hardening off for a couple of weeks – do this gradually, as a sudden drop in temperature can cause bolting. It may be beneficial to warm the soil before planting. Kohlrabi also transplants less well in warm weather, so aim to plant out in mid- to late spring.

Choose a suitable area and get it ready for planting – see Preparing the ground, above. Carefully remove the young plants from their modules without disturbing the roots, and plant them 15cm (6in) apart, in rows 30cm (1ft) apart.

Kohlrabi does need some ongoing attention, as it can be prone to bolting if too dry, too cold or too hot. So make sure the soil doesn’t dry out, and apply mulch to hold in moisture. Plants can also be damaged by various insects, so put protection in place.

In hot, dry conditions, kohlrabi can turn woody or bolt (flower prematurely), so keep the ground moist. Early and late crops tend to be more successful, as they avoid summer heat. Harvest when young and tender, especially if conditions turn dry. Cold temperatures can also cause bolting, so avoid sowing too early outdoors, and take care to harden off indoor-sown plants.

Being a brassica, kohlrabi is potentially susceptible to the usual brassica problems, but as it’s quite fast growing, it’s generally less affected than many of its slower relatives. Cabbage caterpillars are the most likely problem, so either cover plants with insect-proof mesh or check the leaves regularly for caterpillars and eggs. For more on these and other issues, see Common problems, below.