Both rhododendrons and azaleas develop flower buds during the summer for next spring’s bloom. They should be pruned right after blooming so they’ll have a full season to develop flower and leaf buds. If you prune them in late summer or early fall, you may be cutting off next year’s flush of bloom. Sometimes it’s necessary to renovate a shrub, and you can expect few if any blooms the following spring. You can prune them in steps, cutting back just one-third of the shrub each year for three years. That way you’ll lose only some of the bloom, and in three years the plant is back in shape.