Answer: These plants are not winter hardy in cold winter areas such as yours. They can be treated as annuals and replaced each year, or you can try to overwinter them indoors. Ideally, they would be moved to a heated greenhouse.
If you want to keep them blooming as houseplants, they need to be brought indoors before the nights get too cold, say 55 degrees or so. Put them in a very bright location and keep watered and fertilized. They will stop blooming if the location is not bright enough or if they are exposed to too much cold before coming indoors.
Alternatively, you can simply overwinter them indoors in a semi dormant state, leaving them outside until nights are in the mid40's and then cut them back, bring them into a cool bright room, water them just enough to keep the soil from drying out completely, stop fertilizing for the winter. In spring when they try to grow again, water more and feed them.
Yet another method is to leave them out later in the season as above, then place them in a cool location that is dark such as a basement and hope they can survive; in this case they would be watered very little and eventually cut back hard and brought out into the light, and fed and watered normally again, in early spring.
You would probably want to lift the tuber that is in the ground and either pot it up or bare root it and pack it in slightly damp shavings to store as one would store cannas for the winter. This would be in a cool dark location (say 50 degrees) and in a paper bag or cardboard box, check on it periodically to make sure it is not moldy indicating it is too wet (dry it off a bit and repack in clean new material) and not shriveling indicating it is too dry (sprinkle with water to rehydrate slightly). Repot in early spring and place in a bright location to resume growth.
In all cases they would need to be gradually reacclimated to being outside next spring and summer.
It takes some experimentation to locate the most ideal conditions depending on the possibilities you have in your home. I hope it works out for you.
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