Depends on the clematis, how big the pot is, and how cold your winters are. Last fall I purchased several clematis from Donahues that were potted up in one gallon sized pots and left sitting outside in direct sun (when the sun was out) until late February when I planted them in the ground. Most clematis are fairly hardy to zone 3 so unless you have some of the more tender varieties, they would probably do okay outside in a sheltered area but where they can still get rainfall. If you want to bring them inside into an unheated garage, I would leave them outside for several weeks after the first hard frost when they will have entered dormancy and then bring them into the garage. Essentially you want the clematis dormant and not likely to break dormancy when you bring it in.

Mostly 1 gallon pots...our winters are typically a low of 40 during the day and 20 at night. Of course, it can and does go lower. I think I might try leaving them outside but I see you are zone 7a. My zone is 6a or 6b, I have seen both reported for my area.

You could always dig holes in the ground and slip the pots into the holes and allow the earth to serve as additional insulation. I am sure they would be fine that way if you want to leave them outside.

Thank you!