Sow a small numbers of seeds every month from April to July for a continuous supply. Don’t be tempted to sow too early as it will bolt if hit by cold weather. The green varieties mature more quickly so sow these first. If you have a polytunnel or greenhouse to plant them out in, you can start sowing much earlier (January on) and keep sowing until right up to October.
The seedlings will be ready to transplant about 4-6 weeks later. Leave 25-30cm between plants and 30cm between rows. Kohlrabi like free-draining fertile soil, but they are far less demanding than other brassicas. It’s important when planting the seedling out, to plant it level with the ground (do not plant too deep as you might with other seedlings). This is because the lower stem is what will swell out to produce the delicious food and if you bury this, it might rot. Water regularly throughout the season as they go woody in dry weather. You do not need to earth up kohlrabi as you would with some brassicas.
Depending on the variety kohlrabi take between six and sixteen weeks to mature. Lift when they are tennis-ball size. Later sowings can be left in the soil over autumn and early winter, but lift before frosts.
Azur Star – early blue variety.
Superschmelz – tender even if allowed to grow large.
Generally easy to grow, but it’s a brassica, so clubroot and the cabbage white butterfly can be an issue. Check the leaves for caterpillars and remove.