Gardenia is an evergreen shrub with glossy foliage and waxy, fragrant white flowers that bloom in late spring to summer. This shrub does not need much pruning, but if it is getting too large or falling out of shape, it responds well to a trim. However, you cannot just prune the gardenia however or whenever you wish, or you may ruin next year's bloom. With the appropriate trimming technique, you can encourage instead of hinder growth of your gardenia.
Wipe the blades of your pruning shears down with rubbing alcohol on a rag to disinfect them. Diseases from other plants can transfer from the shears and infect the gardenia.
Cut out any dead branches or branches that are broken, diseased or weak. Cut clean through the branch right outside the branch collar, where it attaches to the trunk of the tree.
Trim any overgrown branches back. Remove as much of the gardenia as you see fit, within reason. A trim will stimulate new growth and the gardenia will grow back and set buds for next season without a problem.