01 May Pruning Rhododendrons: The Gardener’s How-To

There are 3 common reasons for pruning a rhododendron – maintenance, shaping and rejuvenation. There seems to be nothing more intimidating to the home gardener than the task of pruning a plant.

Left to their own devices, rhododendrons can achieve heights of 15-20 feet. Hardly the choice in front of the living room picture window. However, by choosing the right variety and putting the right plant in the right place you can avoid any unnecessary pruning in your future. For that reason… here a few helpful ideas that should make this job a lot easier.

1 . Why prune?

Proper pruning keeps plants healthy. It is an effective means of removing diseased or damaged areas of the plant. Pruning is a good way to control the size of the plant. Also, it helps keep the plant from growing into other plants and impeding their growth. You certainly don’t have to look too far to find an example of a foundation planting that seems to be gobbling up the house.

2. Proper rhododendron pruning technique

Rhododendrons, like most flowering evergreens are easy to maintain and require only light annual pruning. This is best accomplished using hand pruners, or secateurs. The right tool will ensure a clean cut. Cuts should be at a 45 degree angle.

3. When is it best to prune rhododendron?

The best time for pruning most flowering broad leaf, and especially rhododendrons, is immediately after flowering and before the new buds set. Take care not to cut back too far on the branch as this will impede future blooming. A general rule of pruning is never cut more back more than one third of the branch or plant.

4. Deadheading & grooming

After the plant has finished blooming, deadheading (remove) the  spent flowers can be done. This will keep your plant neat and attractive and also encourage more blooms next season. Pinch the flower head between your thumb and forefinger at a point where the stem is attached to the main woody stem. The spent blooms should snap away easily. Be careful not to damage the newly emerging buds or you might lose next years blooms. The best time to deadhead is right after the blooms have faded and before new buds set.

5. Keeping your rhododendrons looking their best

Although regular pruning is not necessary, proper grooming and removal of dead wood can keep all your broad leaf evergreens handsome for years to come.  Rhododendrons are shallow rooted and will benefit from a layer of mulch. This will keep the soil cool and retain moisture in the heat of the summer. Furthermore, mulch will protect it from damage from heaving during the winter. Rhododendron, like all evergreens, should be fed with a fertilizer formulated for acid loving plants before and after flowering.

You can find information about rhododendron diseases here.

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