The best time to prune azalea bushes is in the late spring and early summer, while boxwoods can be pruned at any point in the year except for late fall. The reason for pruning determines how the bushes should be pruned.
Azaleas thrive when pruned after the current year's blossoms drop off but before the coming year's buds develop. In most areas, the developing buds emerge by July, so pruning for the year must be done before then. This flowering bush looks best with a natural shape, so prune accordingly. Remove the branches that don't fit that shape. To bring new life to a lackluster azalea, prune between three and five of the largest branches by no more than half. The bush produces new growth from wherever it is cut.
Boxwoods, unlike the flowering azalea, can be trimmed while dormant in the winter, or during the spring and summer growing season. Take care not to trim in the late fall to allow the new growth time to harden off before freezing temperatures set in. Younger boxwood shrubs need more drastic pruning than older, well-shaped bushes. Because this hardy evergreen grows thicker and more dense with pruning, removing stems from the interior of the shrub is necessary for proper air and light circulation. Use caution not to remove too much of the shrub at one time to avoid killing it.