There are more than a thousand species of rhododendrons that grow around the world from Asia to Europe. According to the American Rhododendrons Society, rhododendrons come in a wide variety of colors and types and there are varieties that grow well in nearly every climate zone, from cold to tropical. Rhododendrons grow into large bushes that can get unmanageable if you do not prune them yearly. Remember, however, that rhododendrons flower on old wood so you should not heavily prune last year's growth unless you want to see fewer blooms.
Dead-head spent rhododendrons blossoms after they are finished flowering. Fine Gardening suggests you cut the flower trusses at the base with pruning shears.
Cut off any damaged, dead, weak or diseased wood from the rhododendrons. Cut the wood off at the base of the branch. This type of maintenance pruning should be done in the summer after the rhododendrons stop flowering.
Cut off any crossing or shaded branches on the inside of the rhododendron plant at the base of the branch. This type of pruning should also be done in the summer after flowering has finished.
Shape rhododendrons in the winter while the plant is in its dormant phase. Cut off any unsightly branches just above any leaves you wish to keep. Cut the newer wood, wood that is no thicker than 1 inch, sparingly as it will produce next year's flowers.