Maryl - you mentioned overwintering in the garage. If you plan to do so, please let them get a lot of sunlight or your growth will be stunted.
I leave my pots outside in the winter. A dose of cold actually helps the iris in their development. Smaller iris, such as dwarfs, need the cold to help them produce blooms. I have never had a rhizome split because of ice or cold. I do put leaves around the bases of my pots though to act as insulation for the roots.
