The Q&A Archives: Pruning Rhododendrons

Question: I have some 50+ year old rhododendrons which are more than six foot high, leggy, and interfering with my other ornamental foundation plantings. I would like to cut back some of the far reaching branches, and top the planting at about four feet. Can I do this without killing the plant and when is the best time to do this?

Answer: Since you have so many of these lareger rhododendrons, you might consider adapting the rest of your foundation planting to accentuate and compliment them rather than trying to adapt the rhododendrons. One of the reasons I wsuggest considering this is that while you can do this, the results will depend on some ongoing maintenance. The shrubs will regrow from below the cut branches as well as from the tips of each cut branch so you will need to work to shape and train the new growth. By removing the tip of each branch you will cause the shrub to grow denser; by doing this carefully to the lowest branches you can make them fill in somewhat at the base. Trimming the plant to be more narrow at the top and wider at the base will also encourage more growth near the ground, but it is not the natural shape of the plant and can be a bit of a job to keep it in that form. Ideally you would trim each branch individually to achieve an allover outline without creating an outer "shell" of growth. The idea is to allow light and air to enter the interior of the plant and thus avoid potential disease problems by maintaining good air circulation and healthy growth. The best time to prune like this is in the spring. If you prune early the shrubs will recover more quickly, but you will also cut off the current year's flower buds. After pruning, be sure to check back on the regrowth every few weeks so you can direct it the way you want it to go. Also be sure the plants are mulched and watered in case of drought.

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