If you move that potted dahlia close to your house and under the eave, then I predict you will have many happy returns of your dahlia tuber. It is the wet that rots the bulb rather than the cold that kills them. Placing the tuber in a garage is another way to store them over the winter. You can dig the tuber our of the pot or just leave it in the soil and move the entire pot into the garage. Keep growing, Marianne Binetti