Rhododendrons don't need a lot of pruning, but a little shaping and cutting back each year helps prevent the shrub from becoming overgrown and unattractive. Pruning at the wrong time can ruin next year's display of flowers. There is no set time of year that is right for all types of rhododendrons. Instead, prune them according to their flowering cycle.
Pruning After Flowering
It is best to shape rhododendrons and cut them back to reduce the size of the shrub soon after the flowers fade. Once the flowers finish blooming, the shrub begins forming the buds for next year's flush of blossoms. If you wait too long to prune, you will cut off the tiny new buds at a time when it's too late for the shrub to form more.
Deadheading is an important pruning task that improves the overall health and vitality of the shrub. Allowing spent flowers to remain on the shrub encourages seed production, which drains the plant of energy needed to grow new buds and shoots. In addition, the area in and around spent flowers provides hiding places for insects. Break or cut the flower clusters from the branches as soon as they fade.
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