For cultivars grown outdoors in the open ground, after flowering has finished cut down to 5cm (2in) above where the single stem breaks into flowering stems. Lift with a fork, shake off any loose soil and remove all the old leaves and any old basal shoots. Store in a cold greenhouse, either in pots, boxes or a prepared bed. Use a general compost and make sure they are not planted too deeply. Water to settle in but keep on the dry side through the winter.
In spring the main stem can be cut down again to about 15cm (6in) from the ground and the plants watered.