All of my containers are either metal or foam/plastic with a minimum of 8" and most of them 12 or larger.. I only have one pottery container and it gets hauled into the garage every year. I tore down an old (100+ years) shed and found a treasure trove of enamel wash pans, plates, coffee pots and cooking pots plus several galvanized buckets. One of the larger containers can't be moved because the whole bottom has rusted out. I don't have a clue what it was used for as its about the size of a bushel basket, has fluted sides that curve around all the way to the center bottom and 2 hanging handles.
Doing more research I found that for perennials to survive over wintering in pots the plants need to be 2 zones colder than your zone. So since I'm in zone 4b I need plants rated to zone 2. If I move them into an unheated garage I can get by with zone 3 plants.
I did some further research for zone 2 perennials and found quite a lot! Even more for zone 3 plants. I made a list of both if anyone wants it tree mail me. I'm sure its not complete but its more than I expected to find.
I also discovered that if you overwinter pots in the garage you still need to water them. I learned that the hard way.