What are your thoughts on removing canopy mass to balance root-pruning?

[SU2]

I'm having trouble finding just where I read about this so am hoping for insight here, but my understanding is that it helps balance the tree if, when doing a root pruning, you also remove canopy mass (ie if you removed 10% of the roots and 10% of the canopy, the resulting roots::canopy balance would be stable)

Hoping for any thoughts/elaborations on this concept, thank you

 

[Paradox]

It's common practice

 

[Brian Van Fleet]

It really depends on the tree. Hopefully you're not repotting now. It's like 95 here, can't imagine PCB right now.
Brent Walston said something like this, somewhere: leave all the foliage and the tree will use what it can and sacrifice what it cannot. We won't know which branches are needed and which are not. Let the tree "decide".

Aside from collecting, however, you should not expect repotting to result in any branch loss. At spring repotting, I rarely, if ever prune the top to make it easier on the roots. Good, attentive watering is best for helping a tree overcome a compromised root system.

Some trees which are left with a lot foliage rebound better after heavy root pruning (junipers). Other trees, like boxwood, seem to do better with your idea of a little off the top = a little off the bottom.

 

[jacob letoile]

I do this for landscape trees. I get over sized trees for free because people want them gone. My machine doesn't dig a big enough ball for the trees I'm digging and I generally get them in late spring/early summer so I try to take half the foliage mass off when transplanting. This is not to balance 'energy' but to reduce water demand. When I take a tree there are very few roots left, nowhere near enough to supply the amount that will evapotransperate from the leaves. By reducing the canopy you make it so that the roots can take up enough water to supply the leaves transpiration requirements. That's my theory anyway, and it seems to work for me. 4 Japanese maples better than 8 inch caliper and 4 crabapples so far with only 1 loss. All in the ground for better than 20 years with no root pruning and 38inch root balls when dug.

 

[Bonsai Nut]

It really depends on the tree. Hopefully you're not repotting now. It's like 95 here, can't imagine PCB right now.
Brent Walston said something like this, somewhere: leave all the foliage and the tree will use what it can and sacrifice what it cannot. We won't know which branches are needed and which are not. Let the tree "decide".

Aside from collecting, however, you should not expect repotting to result in any branch loss. At spring repotting, I rarely, if ever prune the top to make it easier on the roots. Good, attentive watering is best for helping a tree overcome a compromised root system.

Some trees which are left with a lot foliage rebound better after heavy root pruning (junipers). Other trees, like boxwood, seem to do better with your idea of a little off the top = a little off the bottom.

So much of what Brian is saying here should also be taken as "guidelines". The best answer is "it depends". And what it depends on, in addition to the timing, the environment, and the species, is the condition of the roots. If you are taking an established tree with a really healthy rootpad, and are repotting it at the right time of year, and you reduce the roots 20%, I'd say not to worry about it - regardless of species.

The challenge comes when you are working with newly collected trees, or trees with severely compromised root systems, or you have to do an emergency repot during the wrong time of year. Then I am careful about how much foliage I leave, and may take extra steps (i.e. misting or humidity tent) to reduce transpiration and reduce the demand on the roots.

 

[Paradox]

I did not have time to elaborate my answer, but BVF and BN are correct.

I do prune when I repot, particularly if I am reducing the root ball to get the tree into a smaller pot. I never remove more than 30%. If I am not reducing the root ball by more than 10% then I don't normally cut back

 

[SU2]

So much of what Brian is saying here should also be taken as "guidelines". The best answer is "it depends". And what it depends on, in addition to the timing, the environment, and the species, is the condition of the roots. If you are taking an established tree with a really healthy rootpad, and are repotting it at the right time of year, and you reduce the roots 20%, I'd say not to worry about it - regardless of species.

The challenge comes when you are working with newly collected trees, or trees with severely compromised root systems, or you have to do an emergency repot during the wrong time of year. Then I am careful about how much foliage I leave, and may take extra steps (i.e. misting or humidity tent) to reduce transpiration and reduce the demand on the roots.

I guess I'm thinking of it in multiple contexts (and was hoping it'd be a simple a/b thing but kind of expected it to be highly variable..), I'm going to be re-potting a bougie and may end up removing some roots (unsure til I'm in there as the tree's orientation is being changed so unsure what the fit's gonna be!) and the thing has just finished putting out a real strong flush of growth that I wasn't sure whether I wanted to touch or not, also keep thinking about my newest collected bougie yamadori since it's collection was essentially a massive root-pruning+re-potting, and the continued wilting (1.5wks now) of the soft shoots on it has it so every time I look at it I think there's just too-much foliage mass for the roots to feed, just cannot help but think that a partial defoliation* is the smart move (I'd probably be defoliating right now if I could make up my mind on which leaves are the smartest to defoliate first, like the younger leaves don't have cuticles and are transpiring the worst, but are also the most capable photosynthetically as well as being the main 'end' of the top/bottom fluid system so are higher in IBA and I'm betting that interrupting that stream is a stress on its own before considering resource(leaf) loss)

(*I've already removed at least 10 leaves but they were dead/almost-dead, am not thinking of being aggressive just removing ~5-10% of the leaves, my gut tells me the energy that had gone to them will now go to the remaining leaves and get this thing vegitating again, have such a bad feeling that if the shoots die-back the entire things gonna die like it's not going to back-bud after the fact since it'll have spent so much resources trying(failing) to keep the shoots alive... Have it in a protected area with plexiglass over its top except for a couple hours I bring it out for sun, can't bring myself to go full-on humidity tent as its trunk already has a little black/green mold/algae and I'm having a terrible problem with that on another bougie, if I tent this thing that mold is going to go out of control and there's a massive, relatively-fresh wound on its trunk like 3-4" above the soil line :/ )

 

[SU2]

I did not have time to elaborate my answer, but BVF and BN are correct.

I do prune when I repot, particularly if I am reducing the root ball to get the tree into a smaller pot. I never remove more than 30%. If I am not reducing the root ball by more than 10% then I don't normally cut back

Do you think there's benefit to doing a partial defoliation instead of (or alongside) any pruning? (in terms of the tree's health/vigor, like how well/quick it gets back to 'normal'?) I wonder this because the idea is to reduce the transpiration of the foliage, and if that can be done by some defoliation *or* by pinching growing tips, it'd seem some defoliation is much less stressful/impactful on the tree than removing apical buds would be (if removing all that auxin in those buds has any significant impairing effect on root development, I'm not sure about that but based on my understanding of roots/hormones I'd imagine it does)

(to be clear I'm talking entirely in terms of the tree's health, obviously things would be altered for any specific tree / what the plan for that tree was!)

 

[SU2]

I do this for landscape trees. I get over sized trees for free because people want them gone. My machine doesn't dig a big enough ball for the trees I'm digging and I generally get them in late spring/early summer so I try to take half the foliage mass off when transplanting. This is not to balance 'energy' but to reduce water demand. When I take a tree there are very few roots left, nowhere near enough to supply the amount that will evapotransperate from the leaves. By reducing the canopy you make it so that the roots can take up enough water to supply the leaves transpiration requirements. That's my theory anyway, and it seems to work for me. 4 Japanese maples better than 8 inch caliper and 4 crabapples so far with only 1 loss. All in the ground for better than 20 years with no root pruning and 38inch root balls when dug.

Thanks, very great to hear this kind of anecdote!! Do you remove any particular foliage? Like, do you remove entire branches or do you just trim an even silhouette? Am wondering whether one of those is better than the other in terms of how much it helps, like if it's solely about leaf-mass that's removed or if things like the fluid under the bark or hormonal considerations come into play?

 

[GrimLore]

(in terms of the tree's health/vigor, like how well/quick it gets back to 'normal'?)

As Greg and others stated - it depends on the plant... That includes the type of plant, what zone it is in, normal watering, fertilizing, and sun/light exposure. Not Knowing or seeing the plant makes it IMPOSSIBLE for me to make any recommendations - I am not sorry but those factors are ALL important

Here the "general" thing I do is 1/3 off the top - 1/3rd off the bottom BUT it does NOT apply to all plants and the time it is done... First rule here is PLANT Health and if it is established

Grimmy

 

[Paradox]

I also have to agree with Grimlore.

It depends.

I am not familiar with how bougies respond to repotting, so I am sorry to say, I don't know what the best thing to do with them is. Hopefully someone with more experience with them can answer

 

[jacob letoile]

Thanks, very great to hear this kind of anecdote!! Do you remove any particular foliage? Like, do you remove entire branches or do you just trim an even silhouette? Am wondering whether one of those is better than the other in terms of how much it helps, like if it's solely about leaf-mass that's removed or if things like the fluid under the bark or hormonal considerations come into play?

I try to remove entire branches and start the tree on a pleasing road. The other thing I do is water the trees every day I remember. I have well drained soil so there is no danger of flooding them and I want to make sure the root ball never dries out. I really do it to remove leaves, and I figure if I'm doing it I may as well make the tree look as good as I can.