How, When, and Why To Prune Rhododendrons
Questions regarding the pruning of Rhododendrons is one of our most commonly asked. There is a wide range of information as well as discrepancies which can be confusing. Many wonder "if" its even possible to prune rhododendrons- and the answer is yes- absolutely!
Pruning your rhododendrons can provide a lot of benefits - not only for the shape of the plant, but also for increase volume of blooms, as well as increased overall health of the plant. Pruning in general is a practice that is best to start when plants are generally younger in age. This helps the plant create a strong framework on which to support itself throughout its lifetime. The genus of Rhododendrons is a large and widely varied group of plants but here are some general guidelines to help:
Above: A Rhododendron which has lost its shape
When to Prune?
In general terms we recommend pruning after flowering has occurred. This will help the plant focus its energy into new growth and not into flower production. Ideally, if pruning happens at this time of year it will be possible to remove the spent flower blossoms which will provide the plant more energy as opposed to seed production. If you are tackling a large plant which has not been taken care of in many years, it is possible to prune the hardwood any time of the season as long as the temperature is above freezing. However, keep in mind to allow the new growth which will be produced from the pruning to have some time to harden off. If done late in the fall, the tender growth can be susceptible to early frosts and cold spell damage.
Pruning General Practices:
We suggest a few general practices which apply to most varieties. To begin, cut out any dead branching. Make the cuts as flush to the stem as possible and don't leave much of the stump. Then remove weak and crossed branching. If there is a mass of existing branching, thin these to give new growth space and air circulation. Finally remove any branching which is laying on the ground. This will help alleviate weevils which climb the branches and eat the foliage.
Pruning for Shape
Most people are pruning to manage the shape of their plants. In most cases the plants have gotten too large for the space and pruning is for compactness and size reduction. When pruning follow the best practices above and make sure to remove damaged branches, sun scorched and scraggly foliage, as well as, any which have been damaged by insects first. The plant can then be pruned back for shape. Make sure to prune back to the nearest leaf or dormant bud.Yearly pruning maintenance can also include tip pruning the new growth's buds to keep the desired shape.
Above: A well pruned and more compact example
Pruning to Rejuvenate
Those plants which have been neglected or outgrown their site can be pruned heartily, preferably in the spring. The key to rejuvenation pruning is to do it over the course of several seasons. In my own garden I remove 1/3 of the oldest branches each year for 3 years. I like to maintain a strong structure on rhododendrons, so i don't always prune back to the ground. On mature plants I keep the base framework and thin a third of the upper portion of the plant.
Pruning for Damage
Many times on older established plantings of Rhododendrons, winter storm, snow, and ice can cause severe damage to plantings. In this situation, follow the best practices above, but if necessary, the plant can be pruned back to the ground. It will re-sprout, but may take several seasons to attain a size and presence of its former glory. In the wild, Rhododendron macrophyllum is often killed back to the ground by fire, only to have it re-emerge from the crown.
Pruning for Transplanting or Moving
Many times established plants need to be moved or transplanted. In these cases follow the best practices as above. Depending on the size of the root ball which has been dug, the branches should be cut back in relative proportion. It is best to do this in the late fall or early spring before growth initiates. We also highly suggest the use of an anti desiccant such as Wilt-Pruf to help with transplant shock.
Don't be intimidated with the thought of pruning your Rhody's. The best approach is to manage your plants on a yearly basis before they get to the point of needing major structural pruning. Be patient and your hard work will come to fruition with a gorgeous blooming Rhododendron every spring!
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- Ulysses Hedrick