Answer: It sounds as though your plant has finished for the season and is going dormant. This usually happens in the fall with the first frost, but yours may have suffered through some stress and is giving up early. I'd treat it as though it is going through a normal dormancy.
Bulbs can remain in the ground in warm winter places. In colder climates such as yours, dig the rhizomes when frost threatens in fall and store them indoors in dry peat moss at a temperature between 60-75?. Calla Lilies grown in a container can be left in the container over winter. Simply bring the container indoors in fall and withhold water completely until you want to start growth again in spring.
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