I doubt there’s any other tender plant so many gardeners, even really good ones, have failed to keep going. Accept a gardenia will not live long and it’s a fair price to pay for such complete loveliness. After all we do not expect a bunch of flowers to endure forever. So if we think of a gardenia as a very long lived bunch of flowers with accompanying foliage then it’s really good value. And those flowers; famous for buttonholes they exude an opulent near decadent perfume from their pristine white or cream, soft almost chamois like petals. 
Now there is not one gardenia but a huge number, mostly from the far east, mostly big trees, usually evergreen, some are thorny, and almost all throw masses of flowers with wonderful perfumes. Their beauty and scent makes the larger species popular in tropical gardens. Several are fortunately less vigorous, more shrub like, and these we grow here. So you most often find G. citriodora which is very compact with pure white flowers, that same gorgeous perfume overlaid with orange flower. The traditional gardenia known here for centuries is G. jasminoides / floride, usually as the most choice double flowered form, flore pleno which reaches waist high. This has a heavy jasmine like overtone with a velvety almost animal aroma that is near addictive. As gardenia flowers age they slowly turn from pure white to rich cream retaining their beautiful double form immaculately even though they are almost ready to drop, and all the time perfuming the air all around. These flowers are given in profusion and being on the tips are neatly set off by the glossy dark green foliage behind, even the shape of these bushes is elegant. Well at the start this is all true. Sadly gardenias are not awfully easy to keep going very long as I said. They need a well drained leaf mould rich compost, high fertility and constantly moist, almost lime free, though they’re not actually ericaceous. Given you might escape the numerous pests they also want a moist buoyant atmosphere, in not too bright almost diffuse light- strong sun is not good, neither heavy shade, likewise they want warmth but not heat, and no draughts. Then with luck, the buds will all stay on, each then opening to a wonderful display. One cause of trouble is most plants sold are three or so rooted cuttings forced into early bloom and very difficult to move on. If you want to have a better chance of a lasting plant then buy from a specialist and get a named specimen growing singly in a big pot. Indeed buy a selection of species as each will be a delight. If good fortune has provided you with a huge greenhouse you could enjoy the tree gardenia G. arborea. This out-performs all others with more profuse, more fragrant, even more beautiful blooms. And amazingly these then set fruits that are aromatic and edible. What more could you ever desire?
