Gardenia is happy in southern zone 8, all of zone 9 as well as South Florida's zone 10. Some species are dwarf and grown as houseplants as well. Various varieties can do different work for your landscape, especially 'Miami Supreme' which has the largest flowers of all. The primary key to gardenias is to start with a highly acid soil. This seems excessive but it always gets results with excellent foliage and fewer pests.
Nematodes are a common problem so fresh soil helps a lot.
Provide reasonable drainage, water regularly but not excessively so as not to strain your gardenia. Critical is to use acid forming fertilizer . Locally, most gardenias have poor foliage for reasons of soil, or fertilizer, or both. Use an acid fertilizer in early spring and throughout the warm months. You may be interested in receiving great tropical plants mail order from Master Gardener.