Exceptions to "top pruning is bad" for collected conifers

[NaoTK]

Why is top pruning bad for collected conifers? People say "conifers get their energy from their leaves/needles" but what about a collected tree with a reduced root mass that is unbalanced to the top? I imagine the tree would collapse if you kept all the leaves, but pruning might restore the balance while the root mass recovers. I understand more leaves would generate roots faster, but not if the tree dries out from transpiration first. I know folks build humidity tents for this reason.

If I collect a conifer but only got 50% of the root mass, would pruning off 25% of the leaves offer an advantage?

 

[PaulH]

Depends entirely on the species. Only on junipers and do I leave as much foliage as possible. Junipers have the ability to absorb water and hydrate from the foliage so newly collected junipers must be misted multiple times a day as they regenerate roots. Other conifers should indeed have the foliage balanced to the roots.

 

[Hartinez]

I think paul nailed it. Junipers are the rule here in my opinion. But on extending species like Englemann or Doug fir id imagine you Could remove said foliage percentages and it would have just as much chance of survival as not. Regardless though, on any newly collected tree, I have been conviced that the foliage, even on junipers is not nearly as important as the quality of root ball and associated field soil. I have no science to back any of this only anecdotal evidence with my own experiences.

 

[Kanorin]

Last winter I collected two shortleaf pines (echinata). The one that I reduced its foliage (~40%) lived. The one that I left foliage intact did not make it. Need more n, but I know which way I’m leaning.

 

[andrewiles]

I've collected quite a few subalpine firs, engleman spruces, mountain hemlocks and western larches over the past few years. My experience has been that if I don't remove top foliage and don't mist I can only successfully collect trees that have good rootballs. Natural rock pockets, etc.

With automated misting and top reduction I can collect a much wider set of trees with poor roots. Or I can do more rootwork at collection time to reduce work down the road. Or I can collect at non-optimal times.

I often take 50% off the top and only get 20% of the fine roots. Wild guess on the latter, but if anything I get fewer roots than that.

I imagine with more top foliage trees can recover faster, but as you say it doesn't much matter if they're dead.

 

[NaoTK]

Thanks for your replies everyone, sounds like we are on the same page here. I will try some light top pruning this year. Yet various pros still say to keep all the foliage. I will ask every pro I know at the pacific bonsai expo this question and report back.

 

[Maiden69]

I know Ryan constantly say for junipers keep, as that is one of the species he works the most that are collected, but I haven't heard anything about pines. What kind of conifer did you plan to collect? I think maybe the saying pines strength is in the roots and junipers in the foliage could apply to this?

 

[woodkraftbonsai]

I had one pine this year that I feel would have survived IF I had topped some of the foliage. My theory was that the tree did not have a good balance between the foliage and roots - this conversation just goes to further my belief in that theory. Thanks for bringing it up!

 

[MrFancyPlants]

I try to leave as much foliage as possible with one exception. If there is a large runner or trunk above what your final tree is to be, I’ll cut off the top for stability. Stability is important for reestablishing roots after collection. You wouldn’t want it swaying in the breeze at that point.
Not, that I have a ton of experience collecting, FWIW.

 

[NaoTK]

I have been collecting englemann spruce, mountain hemlock, subalpine fir and have had great success without pruning, but I also got most of the root ball. But last year I got a spruce with few roots and it later died.

This week I collected a couple questionable spruce (I decided the plural of spruce should be "sprice") and I just went out and top pruned them. I have too many trees and am happy to experiment.

 

[InstilledChaos]

From a physiology standpoint the science (as applied to landscape plants) say to keep all the top growth. Pruning the top growth leads to hormonal signals to replace solar panels at a time when you want all the energy driving root recovery. In addition, obviously less leaves means less energy for root growth. The scientists who advocate this approach say that if there is an imbalance the tree will shed the least energy positive branches and keep the most beneficial. Obviously, in bonsai we may not want to leave these decisions to the tree, so there may be instances when we want to proactively make those cuts. However, this is why I tend to lean on the side of not touching the top if at all possible.

 

[sorce]

I think the reaction to the action, what and where you are cutting, is more important to think about than just to cut or not.

Cutting every next year's fat juicy leader candles isn't the same as removing a bunch of interior needles, or even one whole half of a tree.

I am a "leave it onner".

I don't believe a tree will transpire what's not there. So I don't think "imbalance" is real in this instance.

Sorce

 

[NaoTK]

Over the last few years I have had success with top pruning on both hemlock and spruce, so beginning this year I am exploring the limits of this approach. PNW species like hemlock, spruce, and fir lend well to top pruning because they back bud or the branching will be rebuilt from the interior. So for these species the approach becomes sacrificing exterior branching to ensure the tree survives collection. I would love to know if anyone else has data points to share regarding top pruning + collecting conifers at any time of the year.

In the PNW we often collect in the fall for reasons discussed here. The conventional wisdom is to NOT top prune because "The top helps generate roots" but I have also experienced limitations with this approach.

1. What about cases where the root/shoot ratio is significantly unbalanced and the tree is doomed to collapse?
We can't always get enough roots, and we can't always know this a priori when choosing a tree. Your choices are to hope the tree survives as is, or to try top pruning to improve the root/shoot ratio. Exceptions are juniper as mentioned above.

2. Does "The top helps generate roots" only apply to Spring collection?
I could see this rule making sense in the context of spring when the tree is actively growing. A tree might power through a root/shoot imbalance before the leaves have a chance to desiccate. But in the fall the tree may languish until spring and collapse. Even in the fall, on a heat mat, there are limitations to "top generates roots" and a tree will still collapse if you don't have enough roots.

3. What is the limit of top pruning on a conifer?
I have removed >90% of the needles on a spruce and if the roots are sufficient the tree will back-bud and keep growing. What are the factors that limit how much foliage we can remove on different conifer species?

 

[River's Edge]

Does "The top helps generate roots" only apply to Spring collection?
I could see this rule making sense in the context of spring when the tree is actively growing. A tree might power through a root/shoot imbalance before the leaves have a chance to desiccate. But in the fall the tree may languish until spring and collapse. Even in the fall, on a heat mat, there are limitations to "top generates roots" and a tree will still collapse if you don't have enough roots.

I think the more accurate statement is that apical growth in branches and trunk has the most influence on root production. ( auxin )
If the healthiest part of the tree is the top then one is removing the strongest influence on root production/recovery. On trees where the top is weaker and a side branch is becoming the new apical leader then this would not be the case.
My point is that assessment of the particular situation could and perhaps should lead to variation in process and outcomes.
I collect mostly conifers and do not remove healthy foliage when doing so. However, I select very carefully those that I deem to be " collectable"
From a tree's growth schedule it is a known fact that the early fall is a renewed growth of roots and trunk thickening for a short period of time similar to the growth that occurs in early spring. This is evidenced easily when one monitors wiring and the times of year it tends to cut in quickly!
On a more technical note pages 162 to 173 in " Modern Bonsai Practise " by Larry Morton ( 2016) mentions some important observations that should be applied to collecting.
1. root production times in conifers.
2. advantages of certain climatic zones for fall repotting. ( milder winters zone 7,8 for example)
3. Lowering stress on roots by removal of weak foliage, diseased branches and dead branches.
4. Fall is time when a greater concentration of photosynthates are present for winter storage and spring push. Less so in conifers but more than average.

From a personal standpoint it seems to make sense that one should stress the tree the least amount possible. Removing healthy foliage at any time seems counter productive. Forcing already damaged roots to use stored energy and limited transpiration to wall off newly pruned areas with limited resources and now limiting the production of photsynthates at a time when it is naturally reducing due to upcoming dormancy.

 

[Lara_Ericacious]

" Modern Bonsai Practise " by Larry Morton ( 2016)

This thread brought page 134-135 to mind. Though on the topic of rootpruning when repotting, but I would say it is relevant to collecting trees too.

He explains that removing both branch tips and root tips removes growth signals at both ends result in a net loss.

 

[NaoTK]

Thank you for your thoughts Frank.

I never thought about the apex of the tree as special compared to other growth points on the tree. As you know, our hemlocks might have 200+ growing tips. I have successfully removed the very top apex as well as half of the side growth points during collection. I wonder if the remaining 100 growth points continue to provide the necessary root production, while reducing the transpiration burden to allow collection survival. But I will think about your comments and experiment with keeping the apex or not.

I collect mostly conifers and do not remove healthy foliage when doing so. However, I select very carefully those that I deem to be " collectable"

He explains that removing both branch tips and root tips removes growth signals at both ends result in a net loss.

Then maybe I should reframe my problem statement as "can top pruning enable the collection of trees that are not otherwise 'collectable'?" I agree that removing top and bottom is not ideal and limits growth signals from both ends. But can we accept such losses in cases where the tree will not survive due to transpiration burden. The collectable trees are not always the most interesting, so I'm trying to expand the limits of collection.

 

[Lara_Ericacious]

"can top pruning enable the collection of trees that are not otherwise 'collectable'?"

At the end of the section I mentioned, morton states:

"Any extra pruning at transplanting or repotting has not been shown by science to promote survival or quicker establishment rate in plants"

I would be interested in a source for this claim, though!

 

[Deep Sea Diver]

Yep!…. Just to get some ground truth and center my thinking of the posts above @NaoTK recent post…

(….which seems a fairly simple situation of creating a new apex…. I’ve seen the top hamper taken off in nature and with repots many times on conifers, wire up a new apex, give good care and bob’s your uncle - things are fine. )

Not disputing the above statements at all. But as a science type find myself wanting more…

…especially Morton’s “removing both branch tips and root tips removes growth signals at both ends result in a net loss.” Seems like something a wise Druid would say? What does this mean btw… doomed to die?

Who would even remove all the branch tips and root tips beside a harvester of Christmas trees? Where’s the data?

Cheers
DSD sends

 

[River's Edge]

Thank you for your thoughts Frank.

I never thought about the apex of the tree as special compared to other growth points on the tree. As you know, our hemlocks might have 200+ growing tips. I have successfully removed the very top apex as well as half of the side growth points during collection. I wonder if the remaining 100 growth points continue to provide the necessary root production, while reducing the transpiration burden to allow collection survival. But I will think about your comments and experiment with keeping the apex or not.




Then maybe I should reframe my problem statement as "can top pruning enable the collection of trees that are not otherwise 'collectable'?" I agree that removing top and bottom is not ideal and limits growth signals from both ends. But can we accept such losses in cases where the tree will not survive due to transpiration burden. The collectable trees are not always the most interesting, so I'm trying to expand the limits of collection.

I have often walked away from " very desirable potentially collectable trees" so I fully understand the urge to stretch the boundaries in certain cases. In those situations I would use every trick in the book to try and make it work. Like humidity tents, greenhouse protection, wooden grow boxes, staged collection ( as in partial root cutting while in situ ) , improving the health and condition of root ball before collection,
Please consider documenting the approach so we can benefit from your experience. I for one would be interested to see progression pictures of example.
Would caution against using MT. Hemlock as a general example for conifers though. They rely on natural fibrous surface roots which are almost always present. Making them a difficult species to extrapolate for the conifers such as pines, fir or spruce that have very different natural root formation.

 

[NaoTK]

Lodgepoles can be kept alive with a minimum of roots, so I was never tempted to prune those.
Spruces and fir are likewise pretty durable, so I have only top pruned a couple especially luxuriant spruces, both with success.
It's really the mountain hemlocks that come with a lot of foliage and makes me want to try top pruning. The very old big hemlocks worth collecting typically have 2-3 very large tap roots 1-2" in diameter and so you are at the mercy of what local fine roots there happen to be.

This was the 3rd time I top pruned a hemlock, in Oct 2023. As collected with @Ruddigger. I was initially worried because we severed two 1" tap roots and the tree had a lot of foliage:


I don't have good records but I took most of the longest extensions back and also topped the tree.


styled in 2024


...and again by ruddigger a few weeks ago


New this year I collected a rather young clump. The young trees like this are easy to collect because they haven't formed a massive tap root yet. In this case I only had to cut a couple 1/2" roots.



Nevertheless, in the spirit of the study I have taken back all of the apexes (they were going to be removed later anyway) as well as all the extraneous extensions. I will be very shocked if this one doesn't make it.


And here is a middle aged solitary tree that is quite ramified. This one required severing one 1" tap root and one 2" tap root, but it had above average local roots, so I am hopeful. This pic is actually after I removed the apex and most of the extensions:


After further removing extensions: The tree still has hundreds of growth points but is more in balance with the root ball.



If I have time it would be good to do a controlled study. Something like 4 identical-ish trees with different top treatments. Try doing a significant (75%) top prune on one to see what happens.