When is the correct time to prune rhododendrons?
Question:
I have a large healthy and very overgrown rhododendron in front of the house. I will be pruning about 1/3 of the plant. I am seeing some sites that advise pruning in late winter when the plant is dormant and other sites that advise pruning right after blooming in the spring. What do you advise?
Answer:
Lynne M. Holland, Horticulture and Social Media Professional
Because a rhododendron is ornamental you have both of those options and both have their pro and cons.
Pruning in the late winter I call my “slash and burn” school of pruning. The plant is dormant so you have less chance of insect or disease issues that might pop up in the cool humid late spring and summer. Since it is an evergreen shrub it is easy to see the shape and also figure out that 1/3 part. If you prune it back 1/3 all-around chances are you will have no flowers this spring. This type of cut is a heading cut and it is for controlling height but the shrub will react by having dense growth at the tips
Early Summer pruning is more “artful” for lack of a better word. You can enjoy the flowers this spring and then begin pruning back right after bloom. The cuts you make can be more targeted and this type of pruning lends itself to a more natural shaping of the plant. Where possible taking out an entire branch to the main trunk or even the ground level. This is a thinning cut and it means that the plant will react by growing new branches lower down as well as also putting flower buds on existing branches during the time of the year the plant is in active growth anyway. This is probably best done over 3-4 years so that the plant does not get misshapen.
It is really a matter of personal style which way you approach it. All pruning should be done with the right tools that are sharp and clean to mitigate any tearing of the bark or spreading of bacteria. This is a good resource for pruning with much more detail and video.