Answer: In USDA zones 8 and 9, you can leave Callas (both hybrid and Aethiopica) in the ground year around. In cooler zones, they should be dug in the fall. For the colored callas, their leaves will start to turn yellow and die. Dig the bulbs and let them dry for a few days. Remove any foliage left and pull off the dry roots. The bulbs can then be stored in a cool spot. They don't have to be put in a bag or stored in soil, they do appreciate good air flow to keep them dry. (they rot if they stay wet).
If you are in a cool zone, you can dig Aethiopica and put it in a pot and bring it into the house. Keep it in a well light area (near a bright window) and you should be able to keep it growing all winter- it may even surprise you with flowers in February.
Of course, there are always exceptions to all these rules- I've heard of bulbs in zone 6 surviving the winter and growing the next year- but these are exceptions. If the ground and bulb freeze, the bulb will die. But you can always leave the bulbs in the ground and treat them as annuals- simply buy new bulbs the next year.
Overall Calla Lilies are pretty easy to grow. We don't all have perfect growing conditions for them, but they will grow almost no matter what! With just a little care, you can have some of the loveliest flowers- try it and see!
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