The best time to prune these shrubs is right after they finish blooming. You can shorten the plants by one third or just shorten long branches. Azaleas can also be sheared like a hedge by removing about 3 inches of the new growth after they bloom. You can also prune back one third of your rhododendron branches so that they are just one foot from ground level. This will cause new growth to sprout from the cut trunks and foliage will fill in at the base of your tree-like rhododendrons. It may take a few years of pruning after blooming to reshape an awkward rhododendron but it is worth the effort. Keep growing, Marianne Binetti