Kohlrabi Growing Guide
Kohlrabi Growing Guide
Its odd-looking shape and little-known standing in the kitchen has put this vegetable in the shade. Yet gardeners who give this brassica a try are in for a surprise - roasted kohlrabi is one simple-yet-delicious way of using up this root veg, or try pickled kohlrabi to preserve it for longer. Here is our essential kohlrabi planting guide.
How to grow Kohlrabi
What do kohlrabi, cabbage, Brussels sprouts, kale, cauliflower and broccoli have in common? Quite a lot as it turns out, as they’re all the same species of brassica – Brassica oleracea. All six vegetables are bred from the same wild cabbages that fringe the Atlantic coasts of Europe and the Mediterranean basin. Each brassica has been selectively bred over time to accentuate a particular trait. Cabbage, for example, has been chosen for its large terminal bud, Brussels sprouts for numerous lateral buds and broccoli for enlarged flowering structures. Kohlrabi has been bred to develop a swollen stem, giving it its nearspherical shape.
To distinguish kohlrabi from other crops of the same species, it has been given the suffix ‘Gongylodes Group’ (cabbage, for example, is in the Capitata Group and broccoli in the Italica Group). Its common name, meanwhile, offers a description of its appearance. Kohl is the German for ‘cabbage’, while rabi is a Swiss German variant of ‘rübe’, meaning ‘turnips’, which it closely resembles, so kohlrabi in English quite literally translates to ‘cabbage turnips’.
How to grow kohlrabi in the UK
Of all the many wonderful vegetables to grow, kohlrabi takes the crown for the most bizarre-looking. Its swollen, bulb-like stem sprouts waxy leaf stalks, giving it an alien, out-of-this-world appearance. With varieties available in dusky pale-green or purple, these eccentric members of the brassica family are sure to raise an eyebrow among those unfamiliar with this versatile crop.
Both the leaves and swollen stem of the kohlrabi are edible and with harvests ready to pick from just 10 weeks after sowing, this is one overlooked crop that deserves wider recognition. Its sweet, nutty taste melds with flavours of turnip and celery, making it perfect for boiling, steaming or grating raw into salads. Its speedy, easy-to-grow nature means it’s the perfect catch crop.
Fit a few rows between longer-to-establish brassicas such as kale or Brussels sprouts. The very first sowings of this veg can be made under cover as early as March, with the final sowings for a winter crop of stems occurring from August right up until the beginning of September.
Soil conditions for growing kohlrabi
Like all brassicas, kohlrabi thrives in soil that is free-draining but moisture-retentive. It prefers full sun and copes well with heat, but will also give an acceptable result in dappled shade. As it doesn’t grow as big as other brassicas, such as cauliflower, it can be kept in slightly shallower soil, which makes it a good choice for raised beds or even containers.
You will, however, need a veg patch that is at least pH 6.0 – if your soil is very acidic apply lime to the ground a few weeks before sowing, or grow your kohlrabi in pots of compost.
Prepare the soil by digging in plenty of well-rotted organic matter. Just before sowing rake in some general-purpose fertilizer, such as blood, fish and bone, or chicken manure pellets. To avoid any disease problems, never follow kohlrabi on from other brassicas. If you are starting your crop off early in spring then set cloches into place a week before sowing to begin warming up the soil.
It’s likely that if you’ve never tried this delicious vegetable before, you’ll want to come back for more. Luckily its quick growth makes it suitable for sowing every three to four weeks to maintain a regular supply of stems from late spring through to midwinter.
To begin, rake the soil down to a fine tilth and pull to the side any remaining lumps or large stones. Kohlrabi is best sown ‘direct’: mark out drills 1cm deep and space them 30cm apart to give the plants plenty of room to expand. Sow kohlrabi seeds very thinly along the bottom and cover them back over with soil. Water along the row after sowing to thoroughly wet the ground.
Kohlrabi plant spacing
For a late crop of miniature veg you can place seeds much closer together, leaving just 15- 20cm between rows to enjoy baby kohlrabi up to the size of a golf ball. Make these sowings at least four weeks before the first expected frost – up to mid-September in the south.
Early sowings made in March will need to be protected from the cooler conditions using a cloche. Remove the coverings once the weather improves and night frosts become less frequent. Once the seedlings have their first set of adult leaves thinning can begin in stages – at first to leave about 5cm between each plant and then to a final spacing of 15cm.
Crops grown for miniature veg have an ultimate spacing of just 3-5cm in the row. Don’t compost the thinnings – the first ones make an unusual salad leaf, while the final batch can be steamed whole.
Growing kohlrabi in summer
Kohlrabi planting season usually starts at the end of summer, with sowings made then being ready by autumn, but they will happily stand through the first half of winter. If plants aren’t quite fully grown by mid-October you can speed things along by setting cloches over the crop to keep conditions that little bit warmer and soil from becoming saturated by persistent autumn rain. Purple varieties tend to be hardier, so perform better later in the year.
Growing Kohlrabi month-by-month
Continue with your soil preparations, taking the chance to dig in plenty of compost or well-rotted manure.
Order in the seed catalogues and make your selection. Try a purple and a green variety for contrast. Modern F1 hybrids are the easiest to grow.
Sow the first batch of kohlrabi seeds into prepared ground, having lightly forked in some general-purpose organic fertilizer beforehand.
Continue to start off batches of seeds as the weather warms. Sow every three to four weeks into drills 1cm deep and 30cm apart.
As day length increases so too will the weed problem. Hand weed at every opportunity and water kohlrabi in warm or dry weather to stop the plants becoming woody.
Harvests of stems should be coming thick and fast by now. Enjoy these in salads or boil them; steam the leaves as a tasty bonus crop.
Sow new batches, switching to hardier purple varieties. Watch out for pigeons and protect seedlings with netting.
Continue sowing kohlrabi every few weeks to ensure that you get a successional crop, rather than having too much all at once.
Make the final sowing of kohlrabi before the middle of the month. Keeping this late crop free of weeds is especially important as light levels decrease.
Cover autumn crops with fleece or, better still, solid cloches to maintain good growing conditions. Continue harvesting stems as they become ready.
Start preparing the ground for next year's crop by digging over your veg plot. This will allow frosts to break down stubborn clods of soil. Incorporate organic matter.
Lift the final harvest of kohlrabi in mild parts of the country. In a warmer winter you can expect stems to stay sound outdoors up until Christmas.
Caring for your Kohlrabi plants + problems
Weeding is important, particularly during the earlier stages when seedlings can quickly become swamped by rambunctious plants. Take a little time each week to pull out any weeds by hand, avoiding accidental damage to your young crops.
A layer of organic mulch between rows will help to suppress weeds, while maintaining a moist, well-structured soil. If pigeons (the most common nuisance) are a problem, you’ll need to cover your charges with some netting until they grow on a bit. Any damaged seedlings can easily be re-sown.
Kohlrabi is pretty easy to grow and is less prone to pests and diseases than some other brassicas. Although plants cope well with heat, allowing the soil to dry out will only result in tougher, woodier stems, so water the crop in dry weather to keep them tender but strong.
If your soil is particularly poor, plants will appreciate a top dressing of fertilizer halfway to harvest – either the same one you used just before sowing time, or a liquid feed such as comfrey or nettle tea. Lightly tickle this into the surface with a hand fork or drench the ground with the feed.
Sowings made at the end of summer will be ready by autumn but will happily stand through the first half of winter. If plants aren’t quite fully grown by mid-October you can speed things along by setting cloches over the crop to keep conditions that little bit warmer and soil from becoming saturated by persistent autumn rain. Purple varieties tend to be hardier, so perform better later in the year.
Growing Peas: Problems to watch for
How to harvest Kohlrabi
The earliest kohlrabi will be ready from May, with the final sowings made in September ready for lifting in late October and into December. Like many similar veg there’s a balance to be met between flavour, texture and size. Leave your kohlrabi to grow too big and the stems quickly become woody and hot to taste. Begin pulling up plants when the stems reach the diameter of a golf ball but allow the majority of the crop to grow on. Tennis ball-size is the largest you should allow them to swell, although the amusingly-named ‘Superschmelz’ can grow to monster proportions without its quality deteriorating.
Although kohlrabi is hardy, in particularly cold spots it is better to lift a late-autumn crop of plants before they get consistently clobbered by harsh frosts – simply trim off the roots and foliage and store the stems in a cool, dry place that’s well ventilated. Stems may also be frozen by chopping them up into smaller segments, blanching in boiling water for three minutes then freezing after cooling them off quickly in icy water and patting dry.
To tell if kohlrabi is bad you can feel if it’s feeling slightly less firm than you’d expect, as this may be evidence of rotting. Kohlrabi leaves are also edible, but most growers produce this veg for its bulb. You can eat kohlrabi greens when young, if you fancy something slightly different from your kitchen garden.
Varieties of Kohlrabi
Kohlrabi varieties to try
‘Kolibri’ F1 Hybrid
If you’re looking for speed, this kohlrabi variety is quick to grow. Plus it’s a compact type with delicious and vibrant purple roots.
Great for later sowings and harvests into winter months, this heirloom variety offers purple skin and white flesh that is versatile however you like to cook kohlrabi. Mild and nutty flavour.
Slow to bolt, this sizeable white variety remains tender and doesn’t become stringy, pop in the oven in a tray for yummy roasted kohlrabi - a simple way to use harvests.