Some rhododendrons reach an enormous size if not pruned. Photo: Oh Kaye, flickr.com
Question: I have a very large rhododendron (2.5 m × 2.5 m/8 ft × 8 ft) that I would like to cut back severely after it blooms. Is that possible? It’s far too big for the space available and I no longer have the energy needed to wrap up such a huge shrub for the winter. I live in hardiness zone 4b.
Carole Guay D’Amours
Answer: Many rhododendrons do turn into garden-grabbing monsters over time, becoming tall, wide and sometimes quite lanky. They far exceed the dimensions you saw on the label when you bought it and probably used when calculating where to place it. (Few gardeners seem to know that the dimensions given on a rhododendron label don’t indicate its final size, but rather its dimensions after 10 years of growth. Thus, after 20 years, if they’re never pruned, they’ll measure approximately twice that.)
Fortunately, yes, you can cut an overgrown rhododendron back quite severely and thus reduce it to a more acceptable size. However, as you already seem to be aware, after such deep pruning, don’t expect it to take on a beautiful shape and abundant bloom for 2 to 3 years.
Rejuvenation Pruning
First, the ideal time to do undertake rejuvenation pruning is not after flowering (that’s when you do light pruning), but rather early in the spring, before the start of the growing season. Cut all the branches about to 60 cm (2 ft) high … and yes, you will need a saw! Some gardeners cut back even more severely, to 15 cm (6 inches) from the ground, but that sometimes backfires, the shock being so brutal that some plants don’t recover.
In the first year, your shrub will start to regrow, producing new stems and leaves, but will probably appear very spindly and unequal at first. It will probably take 2 or even three 3 years before it really fills in and starts to look good again. And it may well not bloom abundantly until the third year either.
Maintenance Pruning
In the future, when your rhododendron approaches the size you want, make a habit of pruning your shrub modestly after it blooms to restrain its development, shortening one branch out of three annually. That way, you can keep it at a more acceptable size even as you enjoy an abundance of flowers each year.
Winter Protection: Don’t Waste Your Time
You mention wrapping your rhododendron up for the winter, but that probably isn’t necessary.
The idea that rhododendrons need winter protection to survive in cold climates is highly exaggerated. Wrapping them in burlap or geotextile may make you feel useful and does keep the wind off, but won’t keep them any warmer, so is generally a waste of time. I’m not saying installing some sort of screen between the plant and the prevailing wind can’t be useful the first winter, while it’s still acclimatizing to local conditions, but from then on, no winter protection should be necessary.
Your rhododendron certainly wouldn’t reach such a large size if it weren’t well adapted! There are many rhododendrons adapted to cold climates: hardiness zone 4 and even 3 and yours undoubtedly belongs to that group. So, in winter, just let it fend for itself.
Pingback: Top 22 when to prune rhododendron
Pingback: How to prune overgrown rhododendron? Explained by FAQGuide
I would cover my small rhododendrons in winter because otherwise the deer devour them. My large plants I don’t bother, however deer prune any new growth they can reach each and every winter.
?
Pingback: Protective Pruning for Houseplants – Laidback Gardener
My rhodendrums are very spindly they have a large oak tree shetering them. Would it help to prune them to encourage more growth.
Yes. That will created denser growth and flowerings. But remember that they’re slow to fully recuperate.
Gads! That pruning should have been more selective. If I were to put the effort into cutting back a rhododendron, I would have left only about five stout canes, and not branched with all those stubs. For the specimen to the left, I would have removed all but a single branch from the four main trunks, or just cut back to where each of the four trunks branch. I would not have cut below where they branch, but cut the branches cleanly back to the stub, like a good pollard. New growth is likely to develop on the branch collars there. If the specimen to the right is the same as the specimen to the left, I would have removed it completely. It is too close to the walkway. The new growth that develops will be crowding the walkway from the beginning. Rhododendrons are innately easy to relocate.
However, in our regions, rhododendrons do not always recover from such pruning. Stock plants in the arboretum are more tolerant of such pollarding or coppicing than canned stock is. Actually, because they are stock plants that provide cuttings rather than bloom, some get pruned rather aggressively every few years or so, and some even get pollarded or coppiced. It is not pretty, but it works for what we need them for. Overgrown canned stock is not so tolerant. We only cut them back if it is the only option, and there are too many of them to can into larger sizes. Some never recover. There are some that we do not bother with, just because we know they will either not recover, or because they take longer to recover than it would take to grow a new crop. Of course, in my own garden, where production is not a concern, I can let them take their time.
Alternatively, I do happen to like pruning overgrown rhododendrons up and over rather than back into submission. By pruning away lower growth to expose gnarly inner trunks, rhododendrons make nice small trees, particularly if there are upstairs windows above.