Gardenias can often get too large for their spot. Their flowers are so beautiful and fragrant, many gardeners don’t want to do anything that retards blooming. These notes from Ted Stephens at Nurseries Caroliniana, Inc. should help:
“Gardenias flower on both old and new wood. Flower buds that will bloom next spring are set in fall , but on varieties like ‘August Beauty’, which flower in August (and have been flowering since May), these flowers come on current season’s wood. However, the flower production in May was from the previous year’s growth.
It will vary depending on variety. ‘Kleim’s Hardy’, the single-flowering form does both also. Its heaviest flower production is in the spring from the previous years growth, but it will continue to grow through the summer and flower on current season’s wood.
With some varieties, like ‘Mystery’, you could probably say that it flowers mostly on old wood. But it is definitely a variety thing.”
Condensing Ted’s words, a gardenia can be pruned just about anytime and bloom a few months later.
The only time to avoid pruning is in late fall, since new growth might be frozen in winter.