I live in east Tennessee and will plant my first gardenia outside. I'm concerned about it this winter. The tag says it will tolerate down to 5 degrees.
Planting Gardenia Outside
Certified GKH Gardening Expert
It looks like East Tennessee is a zone 7 https://www.gardeningknowhow.com/planting-zones/ Gardenias are rated for USDA planting zones 8-11. Since you are on the fringe/outskirts of the planting zone I would say that if you took extra steps to winterize your gardenia during cold snaps (by covering with a blanket or cardboard box) then you should be able to make this work.
For more information on Gardenia winter care, please visit the following link: