no reference

If they are out in the ground, as soon as we have frost the tops will go black, clean off the frosted bits and bury them in compost and hope they get through the winter. If you have got a greenhouse you can lift them and pot them up, keep them in the cool greenhouse over the winter.

I usually use a few as houseplants during the winter; they seem to be quite happy about it and continue to grow and flower. These then serve as 'cuttings mothers' for more plants next spring.
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