Looking for a unique and rewarding vegetable to add to your garden? With its unusual, alien-like appearance and crisp, peppery flavour, kohlrabi is a wonderful choice. A member of the brassica family, it's as delicious raw in a slaw as it is roasted or stir-fried.
Perhaps surprisingly, kohlrabi is a fast and easy-to-grow crop, making it hugely satisfying for gardeners of all skill levels. Knowing how to grow kohlrabi gives you a versatile vegetable that's packed with nutrients. Here's everything you need to know about growing kohlrabi successfully in your garden or polytunnel.
How to grow kohlrabi from seed
Growing kohlrabi from seed is a simple and rewarding process. For the best results, you can start the seeds indoors in early spring. When temperatures climb, you can sow directly on the ground from spring through summer for crops in autumn and even early winter.
Gather small pots or module trays and fill them with a quality, peat-free seed compost. Sow two seeds per module, about 1cm deep, and water them gently. Place the pots on a warm, sunny windowsill or in a heated propagator inside your
polytunnel. Germination should occur within 10-14 days. Once the seedlings have emerged, thin them out to promote growth.
If sowing in the ground, ensure the last frost has passed and use a
cloche to protect tender plants. Purple varieties of kohlrabi tend to be hardier and more suitable for sowing in the earlier or later ends of the growing season.
How to plant kohlrabi
Your seedlings are ready to be planted out when they're about 10cm tall and have developed a few true leaves. Before moving them outdoors, it's important to acclimatise them to the cooler conditions over 7-10 days. You can do this by placing them outside during the day and bringing them back in at night.
When you're ready to plant, choose a sunny, sheltered spot with fertile, well-drained soil. If your soil is particularly heavy, improve it by digging in plenty of well-rotted manure or garden compost. Plant your young kohlrabi firmly, ensuring you don't bury the swollen stem base. Space them at least 20-30cm apart to give the bulbs room to swell.
When to plant kohlrabi
For a continuous harvest, you can sow kohlrabi seeds successionally from
March until late
July. Early sowings made in March and
April will benefit from the protection of a
cloche or
polytunnel to shield them from the last of the frost. Direct sowings outdoors can begin from late April or
May, once the risk of hard frost has passed.
Caring for kohlrabi
Kohlrabi is a relatively low-maintenance crop, but a few key steps will ensure a successful harvest.
- Watering: This is the most crucial step. Kohlrabi needs consistent moisture to develop tender, sweet stems. Water the plants regularly, especially during dry spells, to stop the bulbs from becoming woody and tough and to prevent bolting (the plant starting to flower).
- Weeding: Keep the area around your plants free from weeds to reduce competition for water and nutrients. A layer of mulch can help suppress weeds and retain soil moisture.
- Feeding: If you've enriched your soil with compost before planting, you may not need to feed your kohlrabi – they're less nitrogen-hungry than similar crops. However, for an extra boost, you can apply a balanced liquid fertiliser once or twice during the growing season.
How big does kohlrabi get?
Kohlrabi plants are relatively compact. The leafy top growth can reach a height of around 30-40cm. The prize, however, is the swollen stem at the base, which is ready for harvest when it reaches the size of a tennis ball, typically between 5-7cm in diameter.
When to pick kohlrabi
Kohlrabi is a quick crop, often ready to harvest just 8 to 12 weeks after sowing. The key is to pick them when they are young and tender. If left to grow too large, the stems can become hard. You can start harvesting from early summer right through to the autumn, depending on when you sowed your seeds.
How to harvest kohlrabi
Harvesting is straightforward. Once the swollen stem has reached the ideal size, use a sharp knife to cut the plant at the base, just above the soil level. You can then trim off the leaves – don't throw them away, as they can be cooked and eaten just like kale or cabbage!
What grows well with kohlrabi?
Kohlrabi grows particularly well alongside
beetroot,
onions,
potatoes and
cucumbers. Aromatic herbs like mint and rosemary can also help confuse pests like the cabbage root fly.
Can you grow kohlrabi in pots?
Yes! Kohlrabi is an excellent choice for container gardening, especially if you are short on space. Choose a pot that is at least 30cm deep and wide to allow the stem to develop properly. Fill it with a good-quality potting compost and plant one kohlrabi per pot. Remember that pots dry out faster than garden soil, so be extra vigilant with watering.
Master growing kohlrabi with Premier Polytunnels
Whether you're aiming for a summer slaw or a roasted autumn treat, there's nothing better than enjoying your first homegrown kohlrabi. Our fantastic selection of
polytunnels and
cloches will help you get a head start on the season and give you the best possible bounty.
To learn more about enhancing your gardening efforts with our specialist, top-quality equipment, please don't hesitate to get in touch. Call us on 01282 811250 or send us an email at
info@premierpolytunnels.co.uk. Download our
yearly planner and read more of our
growing guides for a month-by-month breakdown of garden jobs.