Answer: Rhododendrons develop flower buds over the summer months for the next spring's flower display. Therefore, rhodies should be pruned immediately after flowering. They do tend to get leggy when not pruned every year or two. Removing more than one-third of the stems and branches in any one pruning session can be really stressful for a rhodie so I suggest you plan to renovate the largest shrubs over a 2-3 year period. Generally, wherever you make a cut the rhodie will respond by generating two new branches. These branches can take 2 years to bloom but in the meantime the plant will fill out and become more dense. So, keeping the one-third guideline in mind, prune your rhodies now and then plan on pruning this time next year to further reduce their size and help them fill out.
Best wishes with your landscape!
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