Knowing how to prune a rhododendron properly has more to do with aesthetics than it does in preventing potential harm to the plant. A remarkably tough plant, the rhododendron can often withstand a complete hacking all the way to the ground and recover in a relatively short time.
But the thing that really bothers some people is to see a rhododendron that has been hat-racked, or pruned to resemble a ridiculous-looking lollipop with no bottom branches bearing foliage (most of them having been pruned) and a swaying-in-the-breeze head.
Go With the Flow of Nature
To those who admire a more natural way of presenting any kind of plant, how to prune a rhododendron entails not making the poor plant look like an inanimate object. So the first thing to keep in mind if you are so inclined to please the more moderate-thinking gardeners in your neighborhood, is to start by taking out deadwood and any limbs touching the ground.
Many people not in the I-want-my-rhody-to-look-like-an-all-day-sucker crowd find simply performing this relatively small amount of pruning quite enough. Sometimes going a step further by cutting out limbs that cross or rub against one another makes for an even more pleasing appearance for the newly pruned rhody. Certainly removing any branches or limbs that harbor disease or insects is a must, as well.
Sometimes knowing how to prune a rhododendron flies in the face of what needs to be done to have vision through a window again or to unblock a much-needed pathway. In cases like these, two choices present themselves: You can either cut the rhododendron back as much as necessary to reach the desired effect, or you can cut the rhododendron back (as well as up to half of its root system with impunity) and move it to a more suitable location.
As you can see, either way, you are going to have to cut the rhody back severely and somewhat indiscriminately. In these situations, whether or not the plant blooms the following season must take a back seat to the more pressing problem at hand.
A Rhody for Every Situation
As you can see, learning about how to prune a rhododendron must go hand in hand with planting them in the first place. There are so many cultivars, hybrids, and varieties available, that when it comes to initially planting one or more, it is always wise to learn about their growth habits first. That way, you wont ever again find yourself in the position of having to perform extreme pruning (or learning to live with blocked windows and pathways).
Learn to plant smaller-growing rhodys beneath windows and along sidewalks, larger ones as specimen focal plants at the end of flowerbeds, and the forty-footers way out in the back of the yard to be enjoyed by the entire neighborhood, and not hindering anything else.
What is perhaps the most important thing about knowing how to prune a rhododendron? No matter whether it is a small, medium, or large rhody, and no matter where you have it in your yard, please, for the sake of all aesthetic-loving humans everywhere, whatever you do, do not turn it into a lollipop!