February to April thinly 1/4in (0.5cm) deep in clean trays or modules of firm pre-watered compost. Keep soil moist at all times.
May to June in final growing space 12in (30cm) apart with 12in (30cm) between each row.
If overwintering in the ground, cover with straw or compost to protect from frost. Keep well watered during dry spells. Celeriac does best under moist conditions.