Rhododendrons: Pruning Rhodies

The following was received via email:

Hi, I'm new and searching for information on how to prune back my overgrown, leggy rhodies. Can you direct me? I am assuming that there is plenty of available information. I just don't know how to get it. Thanks. Judy

 

Generally Rhodo pruning is carried out after blooming is done. For aggressive methods to reduce overgrown plants you can do reduction pruning, look for dormant or latent buds on the stems that are to be reduced and prune slightly above them to encourage the bud to open and develope. If you wish to prune aggressively, consider the 1/3 method, prune 1/3 of the old mature growth back very hard and do the second 1/3 the following year, the third year reduce the remaining plant parts and you should be well on your way to a recovering and reshaped plant.

 

Paul, some Rhododendrons will survive your 1/3 method but some will not; it would kill them as some Rhododendrons do not regenerate from growth older than 2 or 3 years.

 

To illustrate

The first picture shows Rhododendron 'America' in a neighbour's yard. It was pruned hard several years ago by a misguided tenant. Notice the plant did not regenerate and fill out as was intended.
The second picture is R. "Fastuosum Flora Pleno'. I actually pulled this plant from the burning pile. One of our pups had chewed of all green growth to the point where the only thing remaining were half a dozen bare branches. It is regenerating very well.

 

Chris, any chance of a short list of PNW regulars that won't handle the aggressive pruning?

 

Paul, unfortunately no such list is available.

To further complicate matters, some Rhododendrons are naturally leggy and all the pruning in the world, should it survive such treatment, will not result in a more compact plant.
One of the leggiest hybrids I know of is R. 'Sappho', photo taken at Darts Hill Garden Park May 25th, 2003, one of Francisca's favourites. This plant will never be more than 1 or 1.5 m (3 or 4') tall, but can easily grow to 6 m (20') across!

 

So I suppose the first step (for the person who originally asked the question) is to get the rhododendrons identified or supply us with the names. Or, lacking that information, should they call in an arborist who specializes in rhododendrons?

 

In my experience legginess in Rhododendrons is usually induced by lack of adequate light. Contrary to popular belief, most Rhododendrons, at least in B.C.'s Lower Mainland, require full sun to thrive. Rule of thumb: the larger the leaves, the more shade a Rhododendron will tolerate/require.
The attached photo is of a 15 year old plant, a little over 3 m (10') in height, that had started to show signs of legginess. Rather than pruning the plant, we simply moved it as the legginess was caused by overcrowding/lack of adequate light.

Of course knowing which Rhododendron you are dealing with would be of help, but the first thing to do is analyze how the plant is situated. Rule out competition from neighbouring plants and any overhead tree canopy.
If the plant is getting enough light, it may be a naturally leggy specimen, in which case no amount of pruning would result in a more compact plant.
If the plant is not getting enough light, either move the plant itself or minimize/eliminate the competition.
Most of the time the latter approach will have the desired effect without any pruning at all.

 

Chris makes a good point.

Most rhodo books, and certainly Greer's Guide, the most frequently used authority, say that some rhodos can't take full sun - but they are talking about full sun in Oregon, about 5 deg. of latitude further south than BC.

While there are some species that will burn if planted in too much sun even here in BC, most of the hybrids, including those noted as needing partial shade by authors like Greer, will do just fine in full sun.

It would be interesting to compare these ratings with what the Coxes say in their various books, as they are yet another 5 deg. or so North.

 

Here in the North Carolina piedmont nothing except Pine trees. Oaks, and Beeches can stand full sun. Ten minutes in August and your head begins to spin.

So, I have a 'Scintellation' planted in shade. It's done well for many years, but is now quite leggy. How shall I prune it? How do I identify "latent buds" in the trunks/limbs?

So what do you recommend for 'Scintellation'?