Thanks for writing. Gardenias are quite susceptible to stress --- so if you just planted it last week, my instinct is that it's probably stressed about the change in conditions and is working on getting established in the new spot.
That said, make sure it's growing in a spot with moist, well-drained soil that has an acidic pH and that it's shaded from the hot afternoon sun. If your soil is not acidic enough, I would add some soil sulfur now, to help start dropping the ground's pH. (And if you're not sure of your soil's pH, contact your county extension office at http://highlands.ifas.ufl.edu/ to learn more about soil testing.)
Take care not to overwater it while it's getting established; it's best to keep the soil evenly moist, like a well-wrung sponge. You don't want the ground to feel wet or soggy for extended periods.
Good luck. I hope this helps!
---Justin, Senior Garden Editor, BHG.com