I was just asked about what to do with Gardenias in this area (Dallas / Fort Worth, Texas for those of you who don't know). He bought some plants from Lowe's. The tag and the Lowe's site said conflicting things as can happen when a plant is well suited for a wide variety of climates.
For the metroplex it's best to find a nice shady place to put them. While afternoon and evening shade are preferred, a little sun here and there won't leave you disappointed as long as it's kept cool. The flowers are the main reason for this as they will tend to wilt in the heat and fall off.
Also make sure there is good drainage and, for those of you who are mainly interested in the flowers, fertilize it. It eats a lot.