I've got a couple big rhodos that are kind of taking over my yard. They're each 10-12' tall, and solid foliage to the ground. I don't want to kill them, but I'd really like to lighten them up, and free up some space underneath by pruning out the bottom branches. Can any rhodo have the bottom branches removed (to give it a more structural, tree-like form) or does that only work on the types that grow like that naturally?
The only aesthetic limit on limbing them up is how it will look when you are done. Generally with evergreen trees and shrubs these look much better branching to the ground. Picture a limbed up Christmas tree, would you buy one that was perched on a bare leg? The exception is those kinds which have interesting and showy bark - and are specimens old and large enough to have already produced a concentration of branches in the upper part of the canopy. Possible cultural reasons for not exposing the bottoms of your shrubs are the need for rhododendrons to have a cool root run and the fact that these do not lend themselves to having new, smaller plants inserted among their roots - if that is what you are planning. These roots are like a sort of tight, brittle woody sod. Consider these factors and then proceed with what seems to best meet your needs.