Kohlrabi Growing Guide

Introduction

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, acclimatise them to the cooler conditions over 7-10 days by placing them outside during the day and bringing them back in at night.

Choose a sunny, sheltered spot with fertile, well-drained soil. If your soil is 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, sow kohlrabi seeds successionally from March until late July. Early sowings benefit from the protection of a cloche or polytunnel. 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: Kohlrabi needs consistent moisture to develop tender, sweet stems. Water regularly, especially during dry spells, to prevent woody stems and bolting.
• Weeding: Keep the area around your plants free from weeds. A layer of mulch can help suppress weeds and retain soil moisture.
• Feeding: If soil was enriched with compost before planting, feeding may not be necessary. For an extra boost, apply a balanced liquid fertiliser once or twice during the season.

How big does kohlrabi get?

Kohlrabi plants are relatively compact. Leafy tops grow around 30-40cm tall, while the swollen stem at the base, ready for harvest, typically reaches 5-7cm in diameter (about the size of a tennis ball).

When to pick kohlrabi

Kohlrabi is often ready to harvest 8-12 weeks after sowing. Pick them young and tender; leaving them to grow too large can make stems hard. Harvest can start from early summer through to autumn, depending on sowing time.

How to harvest kohlrabi

Once the swollen stem reaches ideal size, use a sharp knife to cut the plant at the base, just above soil level. Trim the leaves—they can be cooked and eaten like kale or cabbage.

What grows well with kohlrabi?

Kohlrabi grows well alongside beetroot, onions, potatoes, and cucumbers. Aromatic herbs like mint and rosemary help deter pests like cabbage root fly.

Can you grow kohlrabi in pots?

Yes! Choose a pot at least 30cm deep and wide. Fill with good-quality potting compost and plant one kohlrabi per pot. Pots dry out faster than garden soil, so water vigilantly.

Master growing kohlrabi with Premier Polytunnels

Enjoy your first homegrown kohlrabi using our polytunnels and cloches to get a head start on the season. For advice, call 01282 811250 or email info@premierpolytunnels.co.uk. Download our yearly planner and read more growing guides for a month-by-month breakdown of garden jobs.