Because gardenia shrubs provide such a heady scent in a landscape, some gardeners resist pruning them at all in fear of reducing or limiting future blooms. As long as you prune a gardenia shrub at the proper time, you will not reduce future blooms. Gardenias do not require extensive pruning to keep their shape. Instead, shape gardenias lightly immediately after they finish blooming in the summer.
Remove spent flowers with the pruning shears as soon as they wilt and fade on the shrub. Clip the spent flowers just under the blossoms with the pruning shears and discard them.
Trim away all dead or damaged stems from the gardenia shrubs immediately after the last flowers wilt from the shrubs. Pruning at this time will not remove future blooms because they have not formed yet on the branches. Cut off all dead and damaged stems at the point they originate from the next-largest branches with the pruning shears.
Shape the gardenia shrub lightly into the shape and size you want it right after the blooming period ends. Use the pruning shears to cut back the branches, always trimming the branches just under leaf nodes.