Trunk Chopping a 8ft tall Betula(Birch) same time as initial nursery repot?

I have a nursery purchased “River/Red Birch” Betula Occidentalis that currently sits at around 8 foot tall. It has, to me, a really interesting trunk base and i think it will turn out nice, plus I got it real cheap. It is currently still in its 3.5-gallon nursery container. This spring, I want to generally apply the things i have learned from Ryan regarding nursery stock: that being to repot it first while it is young and full of energy with tons of foliar mass, so that I can attack the roots pretty vigorously. Given that it is going to be a trunk chop, I have elected to plant it in an 8inch cedar-wood square container (3 in deep), to give it perhaps a bit more than a full-on Bonsai pot, to aid with its trunk chop recovery. But what I am trying to wrap my head around is: when actually IS the best time to do this trunk chop? I have poured over Denis Vojtilla’s content, and have a good idea of where i want to make the chop (something like 12-16 inches from root base, paying close attention to latent buds) but no idea when, or even what order to do it in.

The way I see it is I have a few options, which would you choose?:

  1. Repot in this mid-March or so into the training flat. Trunk chop in autumn (or next spring even)
    -The worry here is that I will have an 8 foot tall tree with loads of foliage, and a tiny base. I live in Denver and it gets hot, i worry about being able to support all that.

  2. Trunk chop it just as the buds swell this year and leave it in the nursery container till next spring.

    • What I would have done had I not heard Ryan make his point about doing root-work first. I do still think in the recovery from the chop that I will have a ton of foliage left, certainly much more than a trained tree to support next year’s repot.
  3. Perform the trunk chop near to/ at the same time as the root work/repot.
    -Obviously the most stressful of the three options, but as a young vigorous nursery specimen might be able to handle it? At least this matches the foliage to the new root volume.

  4. I could repot at bud swell, and trunk chop at post-flush-hardening.
    -a compromise between #1 and #3… Might be less stressful than #3, but I also “waste” a lot of energy on foliage that I will ultimately remove soon after. I would have to wait until the tree is in energy positive, for sure.

Anyway - thanks in advance. If there is some resource i could read i would love to. I also have a much smaller privet that is in the same boat, but being only 3.5 foot tall, all the issues are a little less. Getting a good system down on how to handle large nursery TREES would really open a door.

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I’d love to hear some thoughts on this as well.

Going from 3.5 gallon container to an 8in x 8in x 3in deep container is probably going to be over a 75% root ball reduction. That seems a little agressive but if you are going to do its probably best on an inexpensive young and vigorous tree. I’d also be concerned with the ability for the roots to deliver enough water to the remaining foliar mass if you dont do some kind of foliar reduction.

Options 1 and 4 seem to have the same risk which is getting through summer with a much smaller number of fine roots and a large foliar mass.

Maybe this is a case where you want to do the chop first? After the chop will the tree still be in development while thickening primaries and thickening/elongating secondaries? Do you already have the structure and secondaries you need? If the tree will still be in development maybe it is best to keep it in a bigger container for a while to enable quicker growth.

Lots of questions, not many answers… Looking forward to hearing from others.

First let me correct myself, it will actually be a 12“x12“x3.25“ box, but still it would be a massive reduction. I should also mention that this would be setup under a 40% shade cloth that’s attached to a fence such that the area gets full morning sun, shade cloth in the mid day hours and the fence blocks the sun in the afternoon and evening. But if i left the full height of the tree, it simply would not fit under the cloth that’s at about 5ft off the ground.

Thanks for your feedback, that’s honestly where i an leaning as well. Even after the chop, given a full year to recover it would have a large amount of foliage to stuff in a major root reduction next year. Then again it will still be in major development for another three years easy, so perhaps rushing to root reduce and repot just isn’t the play at all

I’m learning a bunch also, not saying you should go one direction or another just throwing out more things to consider (as if that helps…).

I’m looking forward to hearing from others because I’m also working on larger nursery stock for the first time, stuff that will need bigger reductions in both roots and foliar. I have pines and elongating species. With the pines it seems a little more clear that I need to repot first and wait a year (or at least until the fall) to do foilar reduction. Pines = strength is in the roots so I’ll need to foliar mass to help generate energy to rebuild the roots. Plus the pines move less water and have a thicker cuticle which means they are not as impacted by transpiration. However the elongating species are moving in the direction of your tree (deciduous) because they move a bit more waterthan pines and their strength is in the vascular tissue.

I have had poor results making two big actions on Betula in the same year…I received a bunch of 12-15foot for free so I ran the experiment (big chop/repot) and now I have 2 less than I started with. My understanding is (energy is stored in the vascular system) your going to want as many solar panels (leaves) out to rebuild the root system if you repot and vice versa. Just because the energy is not stored (mainly in either the roots or solar panels such as (junipers/foliage) (pines/Roots) does not mean you can do both actions in a season or even a year and expect the tree to thrive. With that being said I am far from an expert and the experiment size was a N2. Hopefully someone with more experience can chime in but thats all I got.

On another topic for your birch. They really love water. I have birch here in Washington state, during summer, if I don’t keep up with the watering the leaves show me by drooping.

While not a birch, I had a nursery European Hornbeam I bought in July in 2021. I posted about it on the Forum QA asking the same questions you have and Ryan advised that I should chop the trunk in the fall, then repot in the spring of 2022. That’s what I did and the tree is thriving. Hope this helps.

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How about some photos.
Full tree, and a closeup of the bottom 1/3 of the trunk area- including the limbs, if ANY(as best you can…)
Would be easier to evaluate, rather than general info.
The privit is an easier call. Just leave a couple of limbs. It will survive.

Yeah will do. I’ll get those up ASAP.

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Shots mostly of the base, like i said it goes straight up 8 feet of clean out done is the straight suckers, but keep most of the nice bifurcations in the trunk.

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Nice tree. Its big enough to see good results quickly, young enough to be resiliant! The end product will be lovely!
Growth habits of Betula. They are understory trees. They have to grow tall fast to survive. THEN, spread by putting out sucker shoots. … Exactly what you have.
My opinion… nows the time… be conservitive… have a three year plan… Watch the applicable Mirai nursery videos. There is plenty of time.
( I assume you are in the northen hemisphere.)
I would…
Right NOW , start by cutting the root suckers. Leave a ~1" stub for dieback. Scrape any shoots. Don’t let anything sprout. Next spring, judge the growth ring on the stub and cut back each. The next spring cut back each shortened stub to improve trunk esthetics. Cut ALL other suckers that grow.
Akso, right now, cut the remaining trunks back by at least half or more ( back to ~36"?). Pick an esthetically good directional bud. Next year, after the tree lets you know how it responds, you can cut back half again. Leave a 1" stub (for dieback ) above a good side limb. Trim ALL side limbs back by ~half, to a good bud or limb (leave a stub).
I would repot this spring. Be conservitive. This is a multi-year process. Don’t bareroot! The pot will be filled with roots… Only cut off 1/3 of the roots now. All the new roots will be in the bottom 1/3 of the pot. These mostly go. The rootball will be complex. Dont over prune… Plan on having several temporary pots ready; some deaper, some shallower. Temporary for two years. It all depends on what the roots look like. Dont bare root. Leave at least 1/3 of old soil. Gently comb out the roots you can.
For this young decideous tree, use a friable + 1/4 organic soil type; plus pumice, akadama, lava if you have it. A well draining mix. The organics will help keep the roots from drying out.
Leave the surface level the same as now. Cut off the tip of that long surface root. While repotting, tie / wire it and pull down into the pot below surface level. This will reduce the final pot width… Secure the tree in the pot with galvanized wire and bamboo sticks (aluminum wire might work… never use copper on the roots.)
Then… leave it alone for two or three summers. Lightly organic fertilize. Maybe trim long new limbs by half each spring before bud break.
Most of the above is applicable to any young nursery tree.
Sorry about the step by step. It may seem complex but is standard bonsai technique.
Hope this helps. Good luck.
Bonsai On!


OK, just to make sure I have parsed your recommendations correctly, I have broken out the “steps” in a time-based order:

Now (Mid-Winter 2023, Zone 5b): Cut all the straight root suckers , leaving ~1” for dieback. Remove any buds and shoots that grow over the year, and from now on.

Also now (Mid-winter 2023, Zone 5b): do my first trunk chop in what will be a series of tiered chops. Something like 36”. Follow rules for directional pruning. 1” dieback allowance. Question I have here is, is right NOW actually a good time? In Zone 5b, it’s still winter. I have them stored in an unheated, attached garage with some decent grow lights hooked up to an astronomical timer (adjust on and off time based on geographic sunrise and sunset, so the plants can react to increasing daylength). So I can keep it from freezing, but it’s certainly not out of dormancy yet. Is it too early to do this?

Spring 2023 (~late march, early April): Repot. But do so tenderly. Remove ~⅓ of the roots, likely the long wrapped ones at the bottom of the nursery container. It is fully root bound. Comb out another ~⅓ of roots, but leave the last ⅓ untouched. I have a selection of cedar grow boxes, and can build more s o i can easily accommodate what the tree needs. I assume the purpose of this step is to get rid of any existing tap root, and to start the process of getting the roots to flatten out and spread horizontally. I will likely have to craft a 12”x12x5in deep cedar pot, or similar it sounds like. For my soils, i have the following witch which i can mix an appropriate substrate: lot of ¼” Diatomaceous Earth, ¼” Scoria (lava),¼” pumice, ¼” pine bark, ¼” zeolite, and of course i can sift commercial peat-moss based potting mix. I was going to go: 50% DE, 25% Pine, 15% pumice, 10% Zeolite. All sifted to remove anything smaller than 2mm and larger than 6mm (my sieves are metric, lol). Another option would be to leave it in the nursery container, but i worry about how rootbound it is.

Next two years: Mostly free growth. However I have heard with the species that like to drop branches, like Betula, you want to trim more often, and don’t leave growth fully rampant. Perhaps that’s better advice to implement AFTER my second trunk chop (Winter/Spring 2024) and really this year and next, leave it to fully grow.

Thanks again!

You have a great grasp of the process.
It is the infinite nuances of the minor details… storage temps, timing, soil types, guaging the trees strength and health… that randomly kill trees.
Share your mistakes as well as your successes!
You are keeping the tree from freezing. MY opinion is you can safely do the apointed work now. I bet your trunks have a green hint…
My trees are still outside at 20F, waiting for night time 35F temps… I usually play the conservative card. I’m in a 5b zone… warmer than you. The last 5 winters have had crazy moode swings!
If you have the tube cut paste I would use it on the sucker stumps. Will keep the the dieback there to a minimum. Maybe on the larger trunk stumps, though not needed nearly as much. Be conservitve, keep the tree alive… I find the play dough type putty less usefull, except on large cuts and pines. It could be used here.
The only repotting comments I would add is:

  1. Include the top ~2" soil layer in the first round and
    outside edge. Don’t go crazy, though. Tease the
    middle third slightly… less on pines and conifers!
  2. Tap root. Be consertive. First round, especially on
    pines. If there are FEW fine roots up high, cut less.
    (I killed several field grown oaks by cutting a single
    tap root too short. I guessed, wrongly, that 20"
    was enough… very few fine roots.)
  3. Soil?.. use what your comfortable with, that has
    worked for you… That being said, what you
    mentioned is reasonable.
    The products labeled diatomaceous earth
    sometimes is clays or other hard crushed rocks.
    (They package, label and sell whatever will absorb
    DE should be very fine diatom silica bodies. 100%
    inorganic, with NO organic ion holding properties.
    It is good for filtering particles, not absorption of
    ions. Drinking water and fish tank filters…
    I am trying the Napa floor dry. What I’ve bought
    was a hard zeolite looking rock… (I am a
    chemist…) that does appear to absorb and
    release ions.
  4. You could go up to 8 mm size (3/8") for this larger
    Bonsai. Dont waste this soil. Not up to 1/2 “, this
    would grow course roots, unless you ARE
    growing out for a larger tree… I mostly use the
    2 mm (1/16”) for shohin or smaller bonsai and
    seedlngs; and add where indicated for moister soil
  5. Your pots / grow box choice is great. Ryan
    advocates using the smallest container that
    embraces the limiting root…
    What I am saying here works for me. It might not for you… The devil is in the details. Watch the Mirai videos! There is an infinate knowledge there (5 years of weekly 2 hour classes and QA sessions!) Some point made by Ryan might hit for you. He does have excellant bonsai…
    Remember, growing and finishing bonsai are different things.
    Keep a log. Record everything; avoid making the same mistake three times…
    Bonsai are only finished … when they are dead…
    Have a beer!
    Bonsai On!
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Ok, so in the interest of sharing this process, in the hopes it adds to the general community knowledge base, I will continue to share the process. Here are my two trunk chops post chop. This is Chop #1 and as such is very conservative, and nowhere near down to the level i want to ultimately take it.

all i had was the cut paste putty, so that’s what i used.

And here is a close up of the base. I couldn’t help myself and spent a little time digging down looking for the root flare:

The fish-eye of the macro lens makes the taper look worse than it is in reality. I know you said cut and pin those roots, but really they look a solid 1 inch above the root flare, and it hink im going to chop em off at repot. The tree appears to have tons of fibrous roots below that and i dont think they provide a substantial amount of water flow.

And as a bonus, here is the other “tree” the privet:

It has amazing root flare at the base (once again, fish eye).

And here they are in my garage setup:

I have an open window just out of shot that has a fan in it that runs when the lights are on. I want it to get cold enough to provide adequate dormancy but not freeze. I shut the window when it drops below 10 outside or so.

The lights are a pair of: UNIT FARM Upgraded 100W Grow Lights, UF2000 Osram LED Grow Light, 3500K Full Spectrum Indoor Plant Light, for 2x2FT Herb Seedling, 3x3FT Microgreens : Patio, Lawn & Garden

Perhaps not enough output for full time growing, but enough to help stimulate them and get them through the winter. Once all the trees are at their more desired height, i’ll also built a bench indoors and drop the lights to be only a foot or so from the tops.

I’m a bit confused as to why you would “tier” your chops. Surely the first chop should be the most extreme, no? That’s what Ryan always says, after repotting to a smaller container, the tree will never ever again have the same kind of vigor as it did in this year just prior to this chop. It will spend next year adapting to the pot and growing new growth, which will be less than what it has now, and it will be in a worse condition for chopping the next year.

Just cut it down to where you want it now (leaving room for die back). It’s a young and vigorous tree (the bark is still green), not some thousand year old yamadori. It’ll take the trauma. Yes, bonsai is a slow process, and deciduous bonsai is even slower, but there’s no need to make it slower than it already is.

Well next year it won’t go into a bonsai pot, but rather a grow box. The box will be certainly much more shallow, but fairly large volume still. Trying to get the roots out wide. I also wonder if u should chop a bit more, not an the way down, but closer. I think the thinking is, if i chop but orange a kid it buds still, the tree will have a lot of foliage still to recover from the mild repot. Then recover it over the next year and take it down again. Then when it’s recovered, push it into the final pot, still with more foliage than with a fully styled tree. Also even cuts like this will push buds on lower parts to sprout and start forming branching, to which i transition more and more load as i chop lower.

I dunno, i can see it both ways.

One thing i think i will do though: right now i have then all chopped to the same height, which will cause about the same growth in each of the three trunks. I want to maintain girth hierarchy with those trunks though, and i think i ought to cut the one i want to maintain the smallest moreso than the other and have the thickest remain tall.