These shrubs make blooms that flower on the prior year’s wood. So you have to be careful when pruning them since buds for next spring will be made this summer, and you don’t want to prune those off. Don’t wait to prune your azaleas and rhododendrons until late summer or even later, or you probably won’t get the flowers you’re looking for next year.
For rhododendrons with large leaves, you want to prune right above their “growth joints” the place where the plant is starting to grow. Just beneath that point is where dormant buds are, so take care not to cut them off. Small-leafed rhododendrons and azaleas can be pruned anywhere along their stems.
Cutting back a rhododendron heavily can stop the plant from flowering for a year or two. You can prune pretty heavily if needed to get better shape for your bushes, just know that they may not flower for a year or more if you do so.
What should you prune away? Check the inside limbs for any that are dead or look weak. Any limbs on the ground or crossing over other limbs should be pruned away, too. You’ll be giving your bush better air circulation and a less hospitable environment for insects and disease.
Deciduous azaleas (that lose their leaves in the winter) differ from rhododendrons in that they can actually be sheared into a hedge. Anywhere you cut them on their stem, they will branch out. If you’re pruning evergreen azaleas, you can shear them after they flower.
Here’s a great how-to video on how to prune your rhododendrons: