Yes, Gardenia thunbergii will grow in sunny situations and doesn't mind alkaline soils, even quite difficult rocky soils. I am unsure about its cold tolerance but it certainly grows very well on the Adelaide Plains, in the Barossa and Clare Valleys. Old 19thC camellia varieties tolerate similar conditions well too tho' they do best where the roots are in a cool shady site with top growth in the sun, or light dappled shade. A mulch of old manure - cow, horse, goat, alpaca, donkey, sheep etc is good mulch and helps to keep the soil and roots cool. Near here there is a plantation of Camellias that were planted in 1846 - all old Italian, French, British, Portuguese and Australian bred. They are small trees and are on a bald hill top and haven't been watered in at least 100 yrs. The old kinds are much tougher than modern kinds.