I doubt that heat is the issue - most LFH clematis (type II and III) are good in AHS heat zones 1-9, which is quite a bit hotter than you are likely to see in Tennessee. And folks grow them in places like Texas and Arizona as well. I would be more concerned about how much water the vines might receive and how deeply they are planted. If they are planted deeply (4-6" above the soil level of most potted clems) and the soil kept evenly moist, they should not be drying out, especially if planted where they receive afternoon shade.

You might want to focus on the viticellas or some of the American species clematis. Drying out in the heat of summer appears to be less of a concern with these.

Thank you, gardengal. I did not know about planting them deeply.