How to Grow Kohlrabi

Most people don’t realise that kohlrabi, despite its somewhat alien appearance, is one of the most forgiving brassicas you can grow in a British garden. I started growing this curious vegetable after spotting it at a farmers’ market in Ludlow, where a fellow grower convinced me to give it a try. The name translates from German as ‘cabbage turnip’, which perfectly describes its flavour profile. While it might look like something from outer space with its bulbous stem and protruding leaves, kohlrabi offers a crisp, mild sweetness that works brilliantly in both summer salads and winter stews. What makes it particularly suited to our climate is its remarkable cold tolerance and rapid growing cycle. You can harvest your first crop in as little as eight weeks, making it ideal for succession planting throughout the growing season.

Growing kohlrabi successfully is about understanding its preference for cool weather and consistent moisture. Unlike some temperamental vegetables, it won’t sulk if you make minor mistakes, though it does have specific requirements that separate a woody, fibrous disappointment from a tender, sweet success. In my experience, the key lies in timing your sowings correctly and keeping the plants growing steadily without checks to their development.

How to Grow Kohlrabi

Before you start growing kohlrabi, it’s worth gathering everything together. The requirements are straightforward, and you probably already have most of these items if you’re an active gardener. I If you are enjoying this article you may also like our content from seed to salad: my guide to growing proper cucumbers.

Seeds and Growing Medium

You’ll need kohlrabi seeds in your chosen variety. I’ve found purple varieties like ‘Azur Star’ and ‘Purple Vienna’ slightly hardier than green types, though ‘White Vienna’ and ‘Quickstar’ grow exceptionally fast. For starting seeds, use a good quality multipurpose compost or seed-starting mix. Module trays work brilliantly for kohlrabi as they don’t appreciate root disturbance during transplanting. If you’re direct sowing outdoors, you won’t need these.

Soil Preparation Materials

Kohlrabi thrives in firm, well-drained soil with plenty of organic matter. You’ll want well-rotted compost or farmyard manure to dig into your beds a few weeks before planting. Garden lime is essential if your soil is acidic, as kohlrabi prefers a pH between 6.0 and 7.5. I keep a simple soil testing kit handy because brassicas really do perform better in neutral to slightly alkaline conditions. A general-purpose fertiliser or blood, fish, and bone will provide the nutrients your plants need at planting time.

Protection and Support Equipment

Fleece or enviromesh will protect your young plants from flea beetles, which can absolutely devastate seedlings in warm, dry springs. I also keep netting available for pigeons, which seem particularly fond of young brassica leaves. A watering can with a rose attachment helps deliver gentle, consistent moisture without washing away seeds or compacting the soil around young plants. You might also find growing perfect peaches in british gardens: a complete guide helpful.

Step-by-Step Instructions

Growing kohlrabi from seed to harvest follows a logical progression. The process differs slightly depending on whether you’re starting indoors or sowing directly outside, but both methods work well.

Starting Seeds Indoors

I typically start my first kohlrabi indoors in late February or early March, sowing into modules on a windowsill or in an unheated greenhouse. Fill your modules with compost, firm gently, and sow two seeds per cell about 1.5cm deep. Water carefully and keep the compost moist but not waterlogged. Germination usually happens within a week at temperatures around 15-20°C. Once seedlings emerge, thin to the strongest one per module by snipping the weaker seedling at soil level rather than pulling it out, which might disturb the roots of the keeper.

Grow your seedlings on in good light to prevent them becoming leggy and weak. I’ve found that plants started indoors benefit from a week of hardening off before transplanting. This means gradually exposing them to outdoor conditions by placing them outside during the day and bringing them in at night, extending the outdoor period over seven to ten days.

Direct Sowing Outdoors

From April onwards, you can sow kohlrabi directly into prepared beds. I prefer this method for summer crops as it eliminates transplanting stress. Prepare your soil by raking it to a fine texture, removing stones and debris. Create drills about 1.5cm deep and 30cm apart. Sow seeds thinly along each drill, aiming for about 5cm spacing. Cover with soil, firm gently, and water well using a rose attachment to avoid displacing seeds.

When seedlings reach about 5cm tall, thin them to 15-20cm apart depending on variety. Early thinnings can actually be eaten in salads. I always thin in stages rather than all at once, which provides insurance against slug damage or unexpected losses. For a continuous harvest, sow small batches every three weeks from April through to August.

Transplanting and Spacing

Transplant indoor-raised seedlings when they have four to six true leaves, typically four to six weeks after sowing. Choose a mild, overcast day if possible, as this reduces transplant shock. Water your modules thoroughly an hour before transplanting. Dig holes 15-20cm apart in rows 30cm apart. Plant firmly at the same depth the seedlings were growing in their modules. Don’t plant too deeply, as kohlrabi develops its edible swollen stem just above soil level.

After planting, water each plant individually and apply fleece or mesh protection immediately. Firming the soil around transplants is particularly important with brassicas. I use my knuckles to press the soil around each plant, then tug gently on a leaf. If the whole plant lifts easily, it’s not firm enough. Pigeons can uproot loosely planted kohlrabi, so this step matters more than you might think.

Ongoing Care and Maintenance

Kohlrabi needs consistent moisture to develop tender, sweet bulbs. During dry spells, water deeply once or twice weekly rather than little and often, which encourages shallow rooting. I aim for about 2.5cm of water per week either from rainfall or irrigation. Mulching around plants with compost or well-rotted manure helps retain moisture and suppresses weeds, though keep mulch away from the stems themselves to prevent rotting.

Weeding is important, particularly when plants are young. Kohlrabi doesn’t compete well with weeds, and cultivation also helps prevent pest harbourage. I use a hoe carefully between rows, but hand weed close to plants to avoid damaging the shallow root system. Feed with a balanced liquid fertiliser every fortnight if your soil isn’t particularly rich, though overfed kohlrabi can become too leafy at the expense of the swollen stem.

Harvesting at the Right Time

This is where many growers go wrong. Kohlrabi should be harvested when the swollen stem reaches roughly the size of a tennis ball, usually 6-10cm in diameter depending on variety. Left longer, they become woody and fibrous, losing that characteristic crisp sweetness. I harvest by cutting the stem just below the bulb with a sharp knife, then trimming off the leaves and roots.

The size guide varies by variety. Fast-maturing types like ‘Quickstar’ are best harvested smaller, while ‘Gigante’ lives up to its name and can be left to grow larger without suffering quality loss. Check your seed packet for variety-specific recommendations. In my experience, it’s better to harvest slightly early than risk leaving them too long. You can succession plant every few weeks to ensure a steady supply rather than trying to store mature plants in the ground.

Common Mistakes to Avoid

Temperature and Timing Errors

One mistake I see repeatedly is sowing kohlrabi too early in cold soil or too late in summer heat. Kohlrabi is a cool-season crop that bolts readily when stressed by high temperatures or long day length. Bolting means the plant rushes to produce flowers and seeds, rendering the stem tough and inedible. I avoid sowing in midsummer for autumn crops, preferring to wait until late July or August when temperatures start moderating. Similarly, early spring sowings should wait until soil temperature reaches at least 7°C. Cold, wet soil leads to poor germination and increases the risk of damping off disease.

Another timing error involves leaving plants too long before harvest. That perfect tennis-ball-sized kohlrabi can become cricket-ball-sized and woody within a week during rapid growing periods. I mark my calendar when I transplant or thin seedlings, noting the expected harvest date based on the variety’s days to maturity. This prevents me forgetting about a patch that’s nearly ready.

Inconsistent Watering and Feeding

Allowing kohlrabi to dry out and then flooding it with water causes the stems to split and crack, ruining your harvest. This problem becomes particularly common during our unpredictable British summers when weeks of drought suddenly break with torrential rain. I try to maintain even soil moisture by watering regularly during dry spells and mulching to buffer against moisture fluctuations. If heavy rain is forecast after a dry period, I actually water the bed beforehand. Counterintuitive perhaps, but pre-moistening the soil reduces the shock of sudden water availability.

Over-feeding, particularly with nitrogen-rich fertilisers, produces lush leaf growth but poor stem development. Kohlrabi doesn’t need excessive feeding if grown in reasonably fertile soil. I prepare beds well with compost beforehand, then feed only moderately during growth. If leaves are deep green and luxuriant but stems remain small, you’re probably over-feeding.

Inadequate Pest Protection

Leaving young kohlrabi unprotected from flea beetles almost guarantees failure. These tiny jumping beetles riddle leaves with holes, particularly during warm, dry springs. Severe attacks can kill seedlings outright or check their growth so badly that they never recover. I cover all brassica seedlings with fleece or fine mesh immediately after planting or emergence, removing it only once plants are growing strongly. Caterpillars from cabbage white butterflies also attack kohlrabi, though they cause less damage than on heading cabbages. Still, check regularly and remove any you find.

Expert Tips

Variety Selection for Different Seasons

I grow different varieties depending on the season. For early spring sowings, purple varieties cope better with variable weather. ‘Azur Star’ and ‘Purple Vienna’ tolerate light frosts that would damage some green types. For summer crops when speed matters, ‘Quickstar’ matures in just eight weeks and stays tender even in warm weather. Autumn sowings benefit from varieties like ‘Superschmelz’, which grows larger without becoming woody and stores better than early types.

White or pale green varieties like ‘White Vienna’ and ‘Logo’ have exceptionally mild, sweet flavour that appeals to kohlrabi sceptics. I often grow these for summer salads where their delicate taste shines. The purple types offer slightly stronger flavour and look spectacular in the garden, though the purple is only skin-deep. All varieties have pale green or white flesh inside.

Companion Planting and Crop Rotation

As a brassica, kohlrabi shouldn’t be grown in the same bed two years running. I follow a four-year rotation, grouping kohlrabi with cabbages, Brussels sprouts, and other brassicas. This reduces pest and disease buildup, particularly clubroot, a devastating soil-borne disease that persists for decades once established. Good companion plants include onions, beetroot, and herbs like thyme and sage, which may help deter some pests. I avoid planting near strawberries or tomatoes, which compete for similar nutrients.

Intercropping fast-maturing kohlrabi between slower crops like Brussels sprouts or purple sprouting broccoli makes efficient use of space. The kohlrabi will be harvested long before the larger brassicas need the room. Similarly, underplanting with lettuce or spinach creates a living mulch that suppresses weeds and retains moisture.

Storage and Succession Planning

Fresh kohlrabi stores reasonably well in the fridge for two to three weeks if you remove the leaves, which draw moisture from the stem. For longer storage, I keep later varieties in a cool shed packed in slightly damp sand, checking periodically for deterioration. However, kohlrabi never stores as well as root crops like carrots or parsnips. The better approach is succession sowing every three weeks from April to August, providing fresh harvests from June through November.

In milder parts of the country, particularly the South West and coastal areas, autumn-sown kohlrabi can overwinter for early spring harvest. I’ve successfully done this in Surrey, though severe winters will kill them. Fleece protection helps, and the gamble sometimes pays off with harvests in March or April when fresh vegetables are scarce and expensive.

Frequently Asked Questions

Can you grow kohlrabi in containers?

Absolutely, kohlrabi adapts brilliantly to container growing. Use pots at least 20cm deep and wide, filled with good quality multipurpose compost mixed with some perlite for drainage. I grow compact varieties like ‘Quickstar’ in containers on my patio, spacing them about 15cm apart. Container-grown kohlrabi needs more frequent watering than ground-grown plants, particularly during warm weather. Feed every week with half-strength liquid fertiliser. The main advantage of containers is movability, letting you position plants in partial shade during hot weather to reduce bolting risk. You can also bring containers under cover if unexpected late frosts threaten early sowings.

Why did my kohlrabi go woody and taste bitter?

Woody, bitter kohlrabi results from several causes, most commonly leaving plants too long before harvest. Once the swollen stem exceeds about 10cm diameter in standard varieties, quality deteriorates rapidly. Heat stress also causes this problem, as kohlrabi grown during hot weather rushes to maturity and becomes fibrous. Inconsistent watering, particularly periods of drought, triggers the plant to toughen up. I’ve found that even perfect-looking kohlrabi can be woody inside if growth was checked by cold, drought, or pest damage. The solution is harvesting promptly when stems reach tennis-ball size, maintaining consistent moisture, and timing sowings to avoid midsummer heat. If you’ve harvested woody kohlrabi, all isn’t lost. Peel thickly to remove the fibrous outer layer, and the centre may still be usable, particularly in cooked dishes where texture matters less.

How do you prevent flea beetle damage on young plants?

Flea beetles are the single biggest pest challenge for kohlrabi growers. These tiny black beetles jump when disturbed and chew numerous small holes in leaves, giving a characteristic shot-hole appearance. Severe attacks can kill seedlings or stunt growth significantly. Prevention works far better than cure. I cover all young brassicas with fleece or fine insect mesh immediately after sowing or planting, burying the edges or weighing them down securely. Keep covers in place for at least four weeks until plants are growing vigorously. Well-watered, fast-growing plants tolerate minor damage better than stressed ones, so consistent moisture helps. Some growers report success with companion planting of aromatic herbs or using garlic sprays, though I’ve found physical barriers most reliable. Flea beetles are worse in hot, dry weather, so spring sowings under protection and later summer sowings when conditions moderate help avoid peak beetle activity.

What’s the difference between kohlrabi and turnips?

Despite superficial similarities and kohlrabi’s German name meaning ‘cabbage turnip’, these are quite different vegetables. Kohlrabi is a brassica where the swollen part is an enlarged stem growing above ground. Turnips are root vegetables, members of the same brassica family but developing their edible portion below ground. The flavour differs noticeably. Kohlrabi tastes mild, sweet, and crisp, rather like a cross between cabbage heart and apple, with none of the mustard bite that turnips can have. The texture when raw is crisper and juicier than turnip. Growing requirements overlap but differ in detail. Kohlrabi prefers cooler conditions and bolts more readily in heat, while turnips tolerate a wider temperature range. I grow kohlrabi primarily for fresh eating and summer use, whilst turnips excel as winter storage crops. In the kitchen, they’re not really interchangeable, though both work cooked or raw.

When is the best time to sow kohlrabi?

Timing depends on whether you want spring, summer, or autumn crops. For the earliest harvests, I sow indoors in late February or March, transplanting in April for June harvests. Direct outdoor sowings work from April onwards once soil reaches about 7°C. The main sowing period runs from April through July for continuous summer and autumn crops. I avoid sowing in late May and June for my area, as these crops mature during the hottest weeks and frequently bolt. Instead, I restart sowing in late July or August for autumn harvests that benefit from cooling temperatures. In milder regions, September sowings can overwinter for spring harvest, though this is a gamble in colder areas. The key is understanding that kohlrabi is a cool-season crop that performs best in spring and autumn. For continuous supply, sow small batches every three weeks rather than one large sowing. This spreads harvest over months rather than producing a glut followed by a gap.

Can kohlrabi survive frost?

Kohlrabi shows reasonable frost tolerance, particularly purple varieties and mature plants. Light frosts down to around -2°C cause little damage to established plants, and some growers claim frost improves the flavour by converting starches to sugars. However, seedlings are far more vulnerable and hard frosts below -5°C will damage or kill even mature plants. I’ve successfully grown autumn kohlrabi through early winter in Surrey, harvesting into December and occasionally January. Fleece protection extends the season further. Spring sowings need protecting from late frosts, particularly after transplanting when plants are adjusting to outdoor conditions. The swollen stem itself is more frost-hardy than the leaves, which blacken and collapse in hard frosts. If frost threatens a mature crop you’re not ready to harvest, earthing up soil around the stems provides some insulation. In exposed or cold areas, it’s better to harvest before severe weather and store the stems in a cool place rather than gambling on their survival outdoors.

Final Thoughts on Growing Kohlrabi

Kohlrabi deserves a place in more British gardens. Once you master the basics of timing, consistent watering, and prompt harvesting, it’s genuinely one of the easier brassicas to grow. The rapid maturity means you can fit it into tight spaces and brief windows in your planting schedule, whilst the crisp, sweet flavour adds something different to summer salads and autumn stews alike.

I particularly value kohlrabi’s versatility. It grows well in containers for gardeners with limited space, tolerates our variable spring weather better than many vegetables, and produces harvests during the often-tricky gap between spring and summer crops. Yes, it looks peculiar, and you’ll field questions from curious neighbours, but that’s part of the fun. Start with a small sowing this spring, harvest when they’re tennis-ball-sized, and I think you’ll be pleasantly surprised. The flavour is mild enough to appeal to reluctant vegetable eaters whilst offering something genuinely different from the standard repertoire. Give it a go, and you might find yourself wondering why it took so long to try this underrated gem.

Author: Megan Walker

Megan focuses on seasonal food, kitchen garden growing, and how households can reconnect with where their food comes from. Her writing blends practical growing advice with ideas for cooking and eating in season. With a passion for fresh ingredients and sustainable living, Megan’s articles help readers make the most of local produce while supporting British farms.