It is generally agreed that the best time to prune rhododendrons is right after they have finished blooming. New growth begins to flush at this time and energy is flowing in the plant, so any pruning will elicit a response in the plant. Another school of thought is to prune the plant in mid winter so that dormant buds can begin to develop as the plant comes out of dormancy. This works well if you live in milder climates like coastal areas. Also, this type of pruning eliminates the flowers for your spring display. If you do not care about the flowers, and live in a mild climate, then this might be a good option.  

To develop a good structure on young rhododendrons, we tip prune them for their first 5 years. You can continue this practice and will be rewarded with plants that have increased branching, and thus more flowers. After the plant is 10 years old, we would not recommend this type of pruning any more.

When your plants have started to flush out new growth, pinch or break any "singles" (only one shoot is emerging). If there are 2 or more shoots emerging, leave them alone. Within a month's time you will see multiple shoots forming where only one had started.

 

Another pruning technique that is used to shape a rhododendron and keep it fully clothed with leaves is called 'selective pruning'. Here we cut back any overly vigorous branches that extend beyond the desired size of the shrub. This type of pruning will cause the plant to "break" out new shoots along the main stems, thus adding foliage where it is needed. If this is done yearly, your plant will become very handsome.  

 

 

When cutting back using this selective technique, there are no rules as to where to cut. Just cut anywhere and new shoots will emerge along the stem from the hidden "eyes" just beneath the bark.

As with all of these types of pruning, we suggest that the plant be fertilized at least 1 month prior to the cutting. This will increase the chances that lots of dormant buds will break out to fill in the shrub.

 

The shrub to the left was cut back on each branch about 1/2 way back from the tip. In a month or 2 the emerging new growth will result in a very "bushy" shrub. This could be done to rangy, leggy plants to rejuvenate the plant.

 

 

Here is a unique way to accomplish your deadheading of the spend blossoms and be pruning your plant at the same time. Are you tired of getting sticky hands from all of that deadheading? If you prune 2 or 3 leaf junctions below the spent blossom structure and leaving at least one set of leaves, you have accomplished both jobs. You can see a 'single' shoot above my hand, and that will be removed as well. The next photo will show the finished pruning of this part of the plant. In a few weeks, many new branches will break out and begin to add lots more foliage to this plant. 

 

Notice that at each prune point I have left some leaves below. The new branches will emerge from where the leaves attach to the stem. Try this method and you will be done faster and have shaped your plant for more branching and more flowers at the same time. 

 

The last type of pruning that will be discussed here is "hard pruning". This technique is employed when a plant has become tall and lanky...let's not beat around the bush...ugly! Or, you just want to bring the plants down in size to enjoy the flowers more. But, a word of warning, once a rhododendron is down-sized, that doesn't mean that it will stay that size. Most of these large shrubs are just that, 'tree' types of rhododendrons, and will, over time, become the size they were before cutting. If you want a rhododendron planted under your living room window, then it is best to choose one that will only grow to 3 ft tall. Rhodies that have been chopped to fit under a window will always need to be pruned, will not flower, and will in time degenerate.

 

Sometimes our rhododendrons grow too big, and we have to prune them back to achieve a smaller plant for the space. Below is the result of our pruning.