Defoliation 101

ABCarve

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This is an experiment to see if defoliating alone will activate dormant lateral buds or if shoot pruning is required. There was an argument made that this reaction was species dependent. I‘d not seen this behavior myself, but I hadn’t carefully observed all of the species in question either as I often combine shoot pruning with partial defoliation. So I‘m trying it in a decidedly non-scientific study in my garden. This is the Japanese maple test after a bit over a week.

In general, I believe that young shoots extending strongly add caliper faster by letting them add foliar mass through continued extension and they are slowed down by pruning. Removal of older leaves on an extending shoot is a compromise. I’m sure it slows them down a bit as you are removing foliage, but it also keeps the shoots in extension mode while also allowing light and air into the interior of the tree to keep backbuds healthy. This is important because extension builds caliper, but it does not build movement or taper. For that you have to cut back and it’s important to have nice healthy interior growth to cut back to.
Ah-ha!! So you’re saying the shoot will stop extending if you don’t defoliate?
 

leatherback

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The shoot will continue extending after defoliation but slower as part of the leaves is gone, hence less energy to power on.
 

markyscott

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The shoot will continue extending after defoliation but slower as part of the leaves is gone, hence less energy to power on.

Will it continue to extend if left alone?

Yes - I contended for continued extension and that activating lateral buds generally required shoot pruning (With or without defoliation). So far it looks to be true that defoliating alone does not activate lateral shoots at least for the trees I tested (Japanese maple, trident maple, ficus microcarpa, crape Myrtle) in my garden. I‘ll post some additional pictures in another week/

s
 

markyscott

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Ah-ha!! So you’re saying the shoot will stop extending if you don’t defoliate?

Not quite. I’m saying that if the shoot is not pruned, it will continue to extend and that dormant lateral buds will not be activated whether the shoot is defoliated or not. Activating the dormant lateral buds requires shoot pruning and will occur on a healthy shoot in which the terminal shoot has been cut regardless of whether that shoot has been defoliated or not. The common denominator is pruning, not defoliation. The implication is that defoliation alone does not cause backbudding nor will not create fine twiggy growth at the end of the branches. To trigger backbudding or the creation of fine twiggy growth at the branch ends requires pruning and it will occur regardless of whether the branch is defoliated. Defoliation is useful for 1) allowing light to get to parts of the tree that are typically shaded, 2) selectively weakening parts of the tree to redirect energy or 3) for creating a nice fresh set of small leaves for the show.

S
 
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Dav4

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Great thread and VERY timely! After reading about partial vs full defoliation techniques with A. palmatum in Meriggioli's wonderful book, I decided to perform partial defoliation on two of my trees to see if it, in fact, would force dormant buds further down on the trunk to activate... very happy with the results. Once I saw buds popping down low, I took my experiment a bit further and went ahead and fully defoliated several of the branches that had already had some foliage reduction... again, very happy with results.

IMG_4135.jpgIMG_4130.jpgIMG_4131.jpgIMG_4134.jpgIMG_4136.jpgIMG_4127.jpgIMG_4129.jpgIMG_4128.jpg
If these trees were significantly more refined, I'd probably be pinching back the new shoots that have popped since being pruned, but both trees are still building trunks and main branches to some degree and I don't want to stifle the vigor each tree has too much.
 

markyscott

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Here’s the Chinese elm shoot experiment. I won’t be able to take this one any further as I cut it off today. But here is how it looked when I did. There was growth from the terminal bud and no swelling from any of the dormant laterals. Up to this point, defoliation alone on a Chinese elm did not appear to activate any of the lateral buds. But it’s just a week and a half, so difficult to say anything super conclusive. Also, there was a little bit of foliage that remained attached to the petiole toward the end of the shoot.

6B2B7E9C-20A2-43AF-B113-EB258F106378.jpegC56257BE-E886-434A-9FC1-635F5E82941E.jpeg
 

ABCarve

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This is a American hornbeam forest I was going to totally defoliate and now trying your method of partial. I know it responds to defoliation but I mostly just cut the big ones off to allow light in. I’m excited to see results. FE1EA33A-0810-4FE0-A2B7-2F5DFE7C5E08.jpeg959A008C-FB9E-4FBF-B858-B7305216ADC5.jpeg
 

choppychoppy

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Not quite. I’m saying that if the shoot is not pruned, it will continue to extend and that dormant lateral buds will not be activated whether the shoot is defoliated or not. Activating the dormant lateral buds requires shoot pruning and will occur on a healthy shoot in which the terminal shoot has been cut regardless of whether that shoot has been defoliated or not. The common denominator is pruning, not defoliation. The implication is that defoliation alone does not cause backbudding nor will not create fine twiggy growth at the end of the branches. To trigger backbudding or the creation of fine twiggy growth at the branch ends requires pruning and it will occur regardless of whether the branch is defoliated. Defoliation is useful for 1) allowing light to get to parts of the tree that are typically shaded, 2) selectively weakening parts of the tree to redirect energy or 3) for creating a nice fresh set of small leaves for the show.

S


So hey, I'll try to get a complete post up but I wanted to show this one pic at least. This is a shoot that was not pruned during the defoliation. There are several that were left. The last leaf pair was removed but the end was not snipped. I am indeed getting the latent buds to pop out. The sections in yellow did not have leaves during the defoliation. Those were just branches with latent buds. The new growth this year was past the red line where you see the petioles of the leaves removed. But for me it's looking like I'm getting the latent buds to pop leaves whether the shoots were cut or not. I'll try to get a complete timeline post in a few more days as the leaves appear a bit better.

2020-06-04_10.24.53.jpg
 

markyscott

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So hey, I'll try to get a complete post up but I wanted to show this one pic at least. This is a shoot that was not pruned during the defoliation. There are several that were left. The last leaf pair was removed but the end was not snipped. I am indeed getting the latent buds to pop out. The sections in yellow did not have leaves during the defoliation. Those were just branches with latent buds. The new growth this year was past the red line where you see the petioles of the leaves removed. But for me it's looking like I'm getting the latent buds to pop leaves whether the shoots were cut or not. I'll try to get a complete timeline post in a few more days as the leaves appear a bit better.

View attachment 306861

Fascinating. I didn’t get that reaction at all on any of the trees I tested. It’s a mystery.
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These guys (Japanese maple, trident maple, ficus microcarpa) have just continued to extend from the tips. This is the reaction I would expect as the terminal bud, if left intact, would continue to maintain high auxin levels, suppressing the lateral buds. Someone smarter than me will have to tell us why we got such a different reaction.

S
 
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choppychoppy

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Fascinating. I didn’t get that reaction at all on any of the trees I tested. It’s a mystery.
View attachment 306877View attachment 306878View attachment 306879
These guys (Japanese maple, trident maple, ficus microcarpa) have just continued to extend from the tips. This is the reaction I would expect as the terminal bud, if left intact, would continue to maintain high auxin levels, suppressing the lateral buds. Someone smarter than me will have to tell us why we got such a different reaction.

S

Im wondering if it has to to do with the fact that elsewhare on the tree i did remove tips. Probably half the tips were cut and half were left. I also do a pretty complete defoliation. Im thinking that the tree is getting enough stimulus in terms of auxin suppression from the tips that were cut to trigger the latent buds everywhere whether it is on a cut shoot or not. Im gonna ask Bjorn about this topic next week. I will update and add the pics with more growth. This is very interesting!
 

markyscott

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Garden of Mr. Hiroshi Takeyama. Owner of Fuyo-en in Omiya Bonsai Village and one of the top deciduous growers in Japan.
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These are his trident maples after defoliation.

S
 

MrWunderful

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Garden of Mr. Hiroshi Takeyama. Owner of Fuyo-en in Omiya Bonsai Village and one of the top deciduous growers in Japan.
View attachment 307208
These are his trident maples after defoliation.

S

Its nice to see extremely ramified and developed deciduous trees “not” in show form, to see that managing the apex strength is something thats done at the highest levels.

Great pic, thanks
 

Gary McCarthy

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Garden of Mr. Hiroshi Takeyama. Owner of Fuyo-en in Omiya Bonsai Village and one of the top deciduous growers in Japan.
View attachment 307208
These are his trident maples after defoliation.

S
Interesting how he completely defoliates the upper canopy and partially defoliates the lower canopy.
 

leatherback

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Cool picture!

Interesting how he completely defoliates the upper canopy and partially defoliates the lower canopy.
Happy to see I understood something right; This is what I have been doing over the last weeks to my trees: leaving ever fewer leaves as you go up in the tree.
 

markyscott

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Here are a couple of additional good sources of information describing the techniques associated with defoliation as I subscribe to it.


Scott

Another really great discussion of defoliation by Peter Tea.


Scott
 

sorce

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Trees will push those lateral shoots because they're healthy.

May or may not have to do with defoliation.

We have to stop thinking that trees only respond to actions we make.

They do just grow.

My POCD elm hasn't pushed any side growth.

Sorce
 

markyscott

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Trees will push those lateral shoots because they're healthy.

That’s a true statement. As previously discussed:
Once the branch is very strong, you can get backbudding. Sometimes it happens without my intervention at all as a healthy branch will just generate back buds. Sometimes you can get back budding when you cut back a strongly growing branch. But I’d let the branch grow until either I had backbudding or until I felt as though it would be highly likely to make them when I cut back.,


May or may not have to do with defoliation.
Much of the discussion has been around this point - it is my contention that defoliating a tree alone will definitely NOT produce backbudding, nor will it activate dormant lateral buds. Those things will happen by either 1) strong, healthy growth or 2) strong, healthy growth combined with pruning.

We have to stop thinking that trees only respond to actions we make.
This is a red herring - I don’t think that anyone here believes that trees ONLY respond to our actions. That would be foolish indeed. But not nearly as foolish as believing that bonsai are created by accident and we just have to water for them to pop into existence without any human action at all.
 
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ConorDash

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But not nearly as foolish as believing that bonsai are created by accident and we just have to water for them to pop into existence without any human action at all.

Wait, what?! Damn it! Now you tell me. Why didn’t someone tell me sooner... *goes outside to work on trees*.
And here I’ve also been watering my trees frequently, like some kinda fool. Can finally stop wasting water..

But, seriously, great thread, great read :). It should be of no consequence but I’m doing similar actions to a Acer P “Beni Maiko”, and a European hornbeam at the moment. Not as experiment, as just normal and best practice. But I’m taking pics, if they can be of any use. Awaiting response from them currently.

Also perhaps more useful, my other Acer P, on some large sacrifice branches left to grow, unpruned or defoliated, started to push a second flush of growth. As far as I see it, this is just purely out of good vigour and strength. So It shows that you may even see this second flush, whether you prune, defoliate, or do nothing. Always loads of variables at play!
But as a very simplified statement, I completely agree with you. And overall I think it’s better for the complete health of the tree, to partially defoliate or leaf prune, to allow air and light in to the trees inner structure.
 
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