I'm also in zone 7. Just apply a heavy 3" mulch for at least a foot in all directions from the clematises. Pine needles, pine mulch, pine bark mulch - almost anything will do. Could you please get a photo so I can understand the flue better? Thanks. If the flue is tall it could deprive them of light - that's my concern.
Did you plant them with a lot of manure and compost and a handful of bone meal? Did you plant them so the top of the roots are 3" below the earth?
Do you have stakes to lead them to the hog panel fence?
Can you remove the flues to mulch and then put the flues back in place (if they're not too tall)?
Did you give them a good drink? They'll need a few good drinks every few days to settle it but please don't drown them.