Certainly you cant keep them out in winter in Michigan - I do in Jacksonville Fla and it has been down to 28 a time or two inside a ceran enclosed shade house. I start a light mist at 33 -34 degrees and it keeps them from freezing . I have had plants with icycles on the flower spikes - that bloomed and were later shown. The duration of the cold is also an important consideration. An excellent writeup about cold can be found at
Ice