The plants therein
Mother Earth is a great insulator against frost. That’s why we have herbaceous perennials which die down at the end of the season, then burst forth again in spring.
Though the topgrowth cannot withstand winter temperatures, the roots are well below ground and out of harm’s way.
Not so with plants in containers, and the most common reason for failure of permanent containerised plants is freezing of the roots.
For a shrub or climber, planted in a pot, which is intended to remain there for many years, there are two basics.
First, it should be planted in a soil or loam based compost (a John Innes or home-made equivalent), rather than a peat based one.
And second, aim for a container 60cm diameter and 35-40cm deep as a minimum. Bigger is better, as far as frost-proofing is concerned.
And if you live in an area prone to hard winter frosts, try lining the inside of your container with thin polystyrene, before you fill with the growing medium.
Every little helps.
And likewise, re-arrange your pots before winter, if you can, bringing them together in groups. They will insulate each other.
And if all else fails, and you still worry about the cracking potential, wrap your pots in bubble-wrap for the worst on the winter.
Not a pretty sight, granted, but it helps greatly.