Trim a gardenia soon after it is finished blooming in the late spring or summer.
Select branches to prune to control your bush’s size and shape as desired. It’s best to choose older branches since gardenias bloom better on newer wood than older wood.
Prune gardenia branches 1/4 inch above parent branch or node. Always use clean pruning tools and make clean cuts that cut all the way through the branch. Do not tear off a branch.
Trim back a first year gardenia slightly if it is growing vigorously, recommends University of Florida. Trim the branches back just a few inches just above a node in early summer and then again in late summer. This type of light pruning encourages a fuller, wider gardenia rather than a tall and leggy shrub.