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Rhododendron pruning – how and when to prune
Last Updated on July 11, 2019 by John
If you have a flourishing rhododendron you may need to consider pruning for a variety of reasons be it maintenance, rejuvenation or shaping your plant. With a rhododendron, pruning is very simple no matter the reason for it and you can create a shrub with abundant flowers, foliage, and dense branches all of which contribute to a wonderful garden. The first thing we would point out is that Rhododendrons don’t require regular pruning and can go years without needing to be pruned with the exception of removing any damaged or diseased branches.
Deadheading rhododendrons to remove spent flowers and diseased wood
When you are ready to conduct maintenance pruning to get rid of dead wood and old flowers, a process called deadheading, you want to start by snipping at the base of any old flower. This forces the limited energy within the plant on new growth rather than on the older flower trusses.
At any time that you notice dead or diseased parts to your plant, it’s time to prune them back. Start at the dead part and follow the branch to the point where you reach healthy wood. At that point, you want to make a cut.
This type of pruning is designed to remove the spent flower clusters which are referred to as trusses and to get rid of any disease dead wood. The reason behind this is that the trusses will eventually take on the form of seeds which seems like a great idea if you want the plant to throw bountiful seeds into the wind but realistically your plant only has so much energy in a given season and that precious energy can be much better spent on new plant growth, new flowers rather than converting dead flowers into seeds.
This type of pruning for your Rhododendron is the simplest form of pruning and literally requires you to walk up, take a cut, and be done with it. It’s also something that should really only be done once a year.
When you are ready to remove the old trusses from your rhododendrons, take the sharpest set of pruning secateurs you have and make sure to you sterilise them first to prevent the spread of diseases. After that, snip at the base of the Truss, approximately 2 centimetres, maybe one centimetre from the emerging new flower growth. Some people simply grab the stem and snap off the trust from the plant using their thumb in their forefinger which works quite effectively most of the time but here and there it might break off and accidentally take some of the newer growth with it which can cause damage. You can avoid these issues by using pruning them off.
If you have any wood on your Rhododendron that was damaged by harsh winters, you should cut it away from the plant. Any stems that are wilting or diseases should also be cut away. When doing this you want to cut below the damaged portion, cutting ever-so-slightly into the healthier would right above any dormant buds.
This type of pruning isn’t required for the health and longevity of your plant, eventually, the flower stalks will shrivel up and convert to seed unless you have a variety that doesn’t set seed. Either way, it helps with the aesthetics of the plant and most rhododendrons can benefit from it.
Pruning for shape
When you prune your Rhododendron for the shape you are literally altering the shape to control how wide or how tall your plant gets, or to encourage dense branching. Unlike a topiary, the technique used to shape a rhododendron can be done to improve the appearance by encouraging increased branching at very specific points.
Most rhododendrons maintain their leaves for roughly three years so a single branch might have a series of whorls and shaping should be done by following a branch from one end to the last whorl of leaves that you want and then cutting from there. You can repeat this as necessary to rejuvenate your plant. This is a type of pruning that should be done at the end of winter when your Rhododendron is still dormant or early to mid-spring with the risk of frost has passed and just before new growth begins. If your plant is already flowering or about to flower, you can prune after flowering.
Rejuvenation pruning of Rhododendrons
In more extreme cases, if your Rhododendron has become overgrown/leggy or you have taken over a new garden that has not been maintained for a while, you will need to utilise a more drastic pruning technique called rejuvenation and the good news is Rhododendrons usually respond well to hard pruning. This type of pruning removes most of the branches and forces the Rhododendron to produce newer growth on otherwise leafless stems. This newer growth starts to mature into a better framework of branches that you can shape over the years in order to cultivate a stunning specimen. This is another form of pruning that you want to do in early spring to mid-spring just before new growth starts but the risk of hard frost has passed. Knowing how to prune Rhododendrons in this fashion will help you when you have a more mature plant.
Pruning Rhododendrons back hard
To do this you need to be cognizant of the fact that rhododendrons typically have three or more main branches all of which shoot out from the crown of the plant. These are referred to as primary branches and they comprise the scaffold of your shrub. Rejuvenation is the only type of pruning that cuts back each of those primary branches at different heights so as to create a staggered arrangement when the newer shoots reach maturity.
Of course in alternative to this is to cut the entire Rhododendron to approximately 2-3ft off the ground. This is something that most plants survive but those that have been weakened by disease or have suffered from poor nutrition might not bounce back.
If you are worried about your plant surviving such hard pruning we would recommend pruning around one-third of old stems to ground level and then reduce the remaining branches by around a third in the first year and then prune by another third the following year.
With the rejuvenation pruning, you want to look at the main branches and keep your eyes peeled for small pink dots which should pepper the surface of the wood. These dots are referred to as latent Buds and they will eventually produce the new branches.
When you are ready to prune a rhododendron rest assured that all three of these methods are very simple. You can utilise all three when appropriate and helped to encourage a healthier and more attractive Rhododendron and don’t worry if you make a mistake because your plant will bounce back very easily.
After pruning care
After pruning we recommend you water well, add a good layer of mulch and feed with a multipurpose feed to reduce the risk of stress over the growing season.