pruning old rhododendrons

lne216June 8, 2009

I have old, very old, rhododendrons. One is a red color and I do not want it to die. They have one single "trunk" and are 15 feet high. How do I prune them? Not sure how to attach a picture or I would.

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rhodyman(SE PA, USDA Z6)

If they are healthy and have a moderate amount of sun, they can be drastically pruned back. This means cutting back to the height you desire and they will fill out.

Cutting back severely does stress a plant. A healthy plant will recover. Experience shows that plants in deep shade are less likely to come back than those with moderate sun.

If you want to be more prudent, cut back about 1/3 each year until you get the size you want.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

    Bookmark   June 9, 2009 at 1:23PM
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Hmmm ... I have native dendrons that big in my yard ... I can prune newer growth and shape them and they fill in, but I tried to prune one way back and it never filled in ... it seemed to me that the old wood would not produce new growth ... I eventually pulled it out and planted something else.

    Bookmark   June 9, 2009 at 9:06PM
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rhizo_1 (North AL) zone 7

mikey, old wood rarely does fill out. That's why proper rejuvenation pruning requires that you cut the plant nearly to the ground, leaving 6 inch stumps (or less). This will encourage new growth from the crown. If the plant is healthy in the first place, it will develop a lot of shrubby, new growth within the very first season.

In the years following such a drastic step, you can do a small amount of careful detail pruning designed to force your shrub to maintain a full shape at all times.

    Bookmark   June 10, 2009 at 11:37AM
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rhodyman(SE PA, USDA Z6)

rhizo, Tyler Arboretum did this big time one year. As I said, those that were in some sun came back. Those that were in nearly all shade didn't come back.

They definitely have dormant buds on old wood and if healthy and in some sun will come back.

    Bookmark   June 10, 2009 at 12:36PM
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[quote]That's why proper rejuvenation pruning requires that you cut the plant nearly to the ground[/quote]

That's been my experience too.

    Bookmark   June 10, 2009 at 9:57PM
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morz8(Washington Coast Z8b)

While MOST healthy rhododendrons respond well to that type of hard pruning, there are some exceptions. According to my tattered old standby rhody book - (and admittedly a somewhat short list)

"Certain species and some named rhododendron hybrids respond poorly or not at all to pruning. Members of the Falconeri series (and 'tree' rhododendrons in general) will not produce new growth from bare wood; rhododendrons in the Thompsonii series also may resent pruning. Some smooth-barked rhododendrons make little if any growth from stumps, while the following hybrids will not give you multiple shoots from below a pruning cut: Alice, Bagshot Ruby, C. B. van Nes, Mrs. C. B. van Nes and Prometheus."

lne216 - what is your goal in pruning your plants? At 15' I assume they've been large for a while, is something prompting your wanting to reduce their height now...i.e. winter damage, a home repair or remodel project?

    Bookmark   June 10, 2009 at 11:27PM
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botann(z8 SEof Seattle)

At 15 t. tall, that's a pretty big bush. If you think of it as a tree instead, and prune accordingly, it can look much better. With a single trunk, it's already got a good start.
I would open it up a bit and shorten some of the longer branches and some side branches so they won't break in a winter snow load.
Think giant Bonsai instead of a bush with maximum blooms.
As Morz8 said, we need to know your reason why you want to shrink it.

    Bookmark   June 11, 2009 at 1:32PM
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rhizo_1 (North AL) zone 7

I love the look of tree-formed shrubs! They can create some vertical architecture out of a sea of green.

    Bookmark   June 12, 2009 at 11:42AM
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I have the same guestion . A 15 tree rodie that has a single trunk and no branchs for the first 6 or so feet. It has been crouded out by the bigger trees and buildings around it . I would like to prune it and move it. Its currently in total shade. Since its so big if I wack it back to a foot will it come back? If so will it quickly grow back into a tree?

    Bookmark   June 14, 2009 at 2:51PM
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If its not broke don't fix it

    Bookmark   July 7, 2009 at 4:08PM
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I have 3 old, leggy rhodies. They are getting too wide, growing into the walkway. The height (about 12 ft.) is not a problem. We have had very cold seasonal weather and the rhodies just finished blooming. Now the temps are suddenly in the upper 80s. Is it too late in the season to drastically rejuvenate now. I could try one plant, but really don't want to add more stress than necessary. What do you think? Should I wait till next year and do only light pruning now?

    Bookmark   June 22, 2011 at 11:48PM
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rhodyman(SE PA, USDA Z6)

After they just finished blooming is the perfect time to cut them back. When you cut the sides back, it would be good to cut back the new growth on the top also to encourage the plants to fill in the bare spots on the sides. When you cut back, new growth that is exposed during the pruning will sunburn. That is normal and looks bad, but the plant will recover.

With the larger leaved rhododendrons (elepidotes), you must prune just above growth joints. Each year as the plant starts to grow there is a visible point where the plant started growth. We call this point a growth joint. Prune just above this point, because that is where the dormant growth buds are located. Don't prune between joints, because there are no dormant growth buds in that area.

As a plant grows, some of the inside limbs will be shaded out and become weak and die. It is a good idea to remove these, plus other weak limbs that are on the ground or crossing over each other. This provides better air circulation and does not provide a place for insects and diseases to start.

Here is a link that might be useful: How to care for rhododendrons

    Bookmark   June 23, 2011 at 9:44AM
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botann(z8 SEof Seattle)

Here's a picture of one of my Rhododendrons I pruned into a tree. It was growing out over the driveway. If it had been growing out over the lawn, I might have cut the lawn back, rather than the Rhody. It's a Anna Rose Whitney X Dcorum.

I would rather go for the form of the plant over the number of blossoms. Blossoms are not a cash crop.

    Bookmark   June 27, 2011 at 2:43PM
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I'm with botann and those who advocate leaving it as a "tree", if you can (btw, great pic, botann!). I could tell you live in the Pacific NW, as your tree has moss on it!

I've been pruning judiciously, the 3 ancient Rhodos near our house and they respond well. I'd just add that pruned "stumps" should probably be sealed, to avoid infestation.

Sadly, this past winter did a lot of damage, so I had to cut back some 5-6 years worth of growth, resulting in shrubs that look like Ichabod Crane ("spindly"). But there is a lot of new growth lower down, so we'll see...

    Bookmark   July 3, 2011 at 12:01PM
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morz8(Washington Coast Z8b)

Mmeolenska, the use of pruning and wound sealants was once thought to be a good preventative practice, but current advice is to skip it - arborists now find it may harbor disease and slow healing, a good smooth clean cut left to seal/heal itself now recommended.

And yes, Mike's (Botann) garden is exceptionally lovely, rhododendrons and otherwise :)

    Bookmark   July 3, 2011 at 3:22PM
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CEFreeman(DC/MD Burbs 7B)

I apologize for not getting it if this question was addressed, but when to prune?

I know lilacs bloom on old growth, so prune the same year as they've bloomed. But azaleas and rhodies? I have a 5 year old Ichabod :) that in ignorance, I probably planted too close to the house. I'd like to fill it out and direct it's growth away from the house.

Shall I tackle it this year? It has dormant buds on the ends of each limb. That would mean no blossoms next spring, right?


    Bookmark   August 15, 2011 at 10:11AM
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morz8(Washington Coast Z8b)

That's correct Christine, pruning now would remove the flower buds and prevent blooming next year. The time to prune is immediately after flowering.

    Bookmark   August 15, 2011 at 10:23AM
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