Grow celeriac as you would with celery, but because it stores well, there’s no need for succession sowing. A single sowing in late March or early April is all that’s required. Broadcast (sprinkle liberally) the seed in to a pot filled with compost. As is the case with celery, celeriac seeds need light to germinate so do not cover the seed with compost. Place the pot somewhere warm (a sunny windowsill or a heating mat) – it’s slow to germinate so don’t expect any action for two to three weeks. Keep the compost moist. Prick the seedlings out in to module trays (one seedling per module) about 2 weeks after germination (when about 3cm tall). If you grow 24 celeriac you can enjoy one a week from October to the end of March. You will need 1m of veg bed for every 9 celeriac (where the bed is 1.2m wide).
After hardening off well, plant out the seedlings in to the bed in May or when the seedlings are 10cm tall. Space the plants 35cm x 35cm apart. Celeriac is shallow rooting which means two things – firstly it will dry out easily so you will need to water well in dry weather (and/or mulch around the plants to conserve moisture). Secondly you need to be careful when hoeing in case you damage the roots.
Celeriac are ready to rock from October onwards. They can be left in the ground in a mild winter (though they can be a little vulnerable to worms etc which will bore inside) or lifted and stored in sand. Use a fork to gently lift the plant, roots and all.