Structural Pruning of Japanese Maples

[0soyoung]

I am still confused as to what would happen if I cut to early or too late?

At some point you will dive in and find out OR you will remain caged by analysis paralysis. Shit happens and it is quite educational. The proof of expertise is how well you recover from it. Masters screw up all the time (but very rarely the same way again and again).

If spring in the UK is say Mar - May(ish), can I assume that first growth phase would be over by June? So chopping anytime in June would be a good rule of thumb?

It varies a bit with climate and cultivars, but acer palmatums generally have three growth spurts (extending shoots) each year. The gaps between are about May and about August. Cut backs generally should be done during these pauses, just before the next surge of extension. In my way of thinking, These hardened stems with hardened foliage are feeding the tree (whereas the extending growth is consuming carbohydrates). I would chop as soon as I perceive a pause in extension, but maybe I being entirely too fussy --> you just need a productive branch close to the chop point.

 

[Cable]

I make trunk chops when the new foliage starts growing, through when the first flush is hardening off.

Thanks for the tip. Last year I trunk chopped a maple in February or early March. It never leafed out. Next year, I have another maple that needs a chop so I'll wait until the buds are open. This one will have buds below the chop, at least.

 

[Adair M]

Japanese Maples have a few particular characteristics that are unique to them.

There is a window of time in the fall to trim and cutback with no “bleeding”. And that period is just after the leaves have reached peak color. For about two weeks. So, the best practice is to remove the leaves, (yes, I know... they’re still pretty!) and cut back to a bud that’s facing the direction you want the branch to grow next spring. Seal the cuts. If, when you make the cut the tree bleeds excessively, stop, and wait a week.

The reason this works is the tree is pulling the sugars out of the leaves, so the flow is away from the tips. The tree shouldn’t bleed.

Another method, more useful in the spring, is to repot when you cut back. Removing the root tips prevents the tree from quickly absorbing water to bleed.

One more: you can prevent bleeding by running a sycle along the inside edges of the pot. This damages the roots just enough to prevent bleeding when cutting back.

 

[Deleted member 21616]

Japanese Maples have a few particular characteristics that are unique to them.

There is a window of time in the fall to trim and cutback with no “bleeding”. And that period is just after the leaves have reached peak color. For about two weeks. So, the best practice is to remove the leaves, (yes, I know... they’re still pretty!) and cut back to a bud that’s facing the direction you want the branch to grow next spring. Seal the cuts. If, when you make the cut the tree bleeds excessively, stop, and wait a week.

The reason this works is the tree is pulling the sugars out of the leaves, so the flow is away from the tips. The tree shouldn’t bleed.

Another method, more useful in the spring, is to repot when you cut back. Removing the root tips prevents the tree from quickly absorbing water to bleed.

One more: you can prevent bleeding by running a sycle along the inside edges of the pot. This damages the roots just enough to prevent bleeding when cutting back.

Thanks for the info @Adair M

All of this seems to presuppose that bleeding matters. In your experience, does it matter?

as with most things, experts seem to disagree on this point! Would love to know what you’ve experienced

 

[0soyoung]

Japanese Maples have a few particular characteristics that are unique to them.

There is a window of time in the fall to trim and cutback with no “bleeding”. And that period is just after the leaves have reached peak color. For about two weeks. So, the best practice is to remove the leaves, (yes, I know... they’re still pretty!) and cut back to a bud that’s facing the direction you want the branch to grow next spring. Seal the cuts. If, when you make the cut the tree bleeds excessively, stop, and wait a week.

The reason this works is the tree is pulling the sugars out of the leaves, so the flow is away from the tips. The tree shouldn’t bleed.

Sugars are being removed from the leaves the entire time they exist in a hardened state - that's what the leaves do, make sugars. The photocenters are made of metabolically expensive nitrogenous compound and proteins. In fall, the photocenters in the leaves are dismantled for removal from the leaf. Chlorophyll is changed into compounds that are colorless, so the green color disappears, leaving the compounds that protected the photocenters to color the leaves: xanthophylls (yellows), carotines (oranges), and anthocyanins (reds to purples).

'Bleeding' is xylem sap - sugary water from the wood. Bleeding occurs as a result of the pattern of overnight chill (near freezing) and daytime warming. This occurs most prominently in spring, before there are any leaves. It is just a coincidence that this pattern of overnight chilling also corresponds to the time of abscission. Otherwise, the two processes have no connection.

Another method, more useful in the spring, is to repot when you cut back. Removing the root tips prevents the tree from quickly absorbing water to bleed.

True, but the cure is worse than the disease, IMHO. Lemme see, the rationale is that loosing a little sugar from the xylem is 'wasting energy' whereas removing roots is not wasting anything? If it bothers one, wait a while (or prune a bit earlier) and it won't happen ('bleeding') and no energy will be wasted.

 

[Deleted member 21616]

'Bleeding' is xylem sap - sugary water from the wood. Bleeding occurs as a result of the pattern of overnight chill (near freezing) and daytime warming. This occurs most prominently in spring, before there are any leaves. It is just a coincidence that this pattern of overnight chilling also corresponds to the time of abscission. Otherwise, the two processes have no connection.
.

If I am understanding correctly, bleeding in the fall would reduce the sugars in the tree and therefore decrease its winter hardiness (by raising the temperature at which the affected area can freeze? - sugar water freezer at lower temps than straight water?) ? This would explain why our local nurseries in Quebec routinely prune in the fall and do not care about bleeding, but also insist that trees be kept between 1-2C (34-34F more or less).

@0soyoung i've seen you post a few times about this, and I am anxiously waiting for your opinion/knowledge on whether spring bleeding affects the tree? So many experts say no, but it is a loss of energy after all? is the energy simply lost of areas that don't matter (the wood/xylem)? Sorry to put you on the spot with the question -- i'm sure a lot of people here value your knowledge (and generosity when sharing it) as much as i do

this is what i found regarding Walter Pall's stance, which seems to make sense if the biology checks out (i don't have the background to confirm whether it does):

"It may bleed, but bleeding IS NOT HARMFUL. Many peole think the tree will bleed to death, they thing it works like a human being. What you see as bleeding is the water that would havve gone into tzhe parts that you cut off. So nothing is lost here"

taken from here: http://walter-pall-bonsai.blogspot.com/2009/04/maples-progressing.html

 

[0soyoung]

If I am understanding correctly, bleeding in the fall would reduce the sugars in the tree and therefore decrease its winter hardiness (by raising the temperature at which the affected area can freeze? - sugar water freezer at lower temps than straight water?) ? This would explain why our local nurseries in Quebec routinely prune in the fall and do not care about bleeding, but also insist that trees be kept between 1-2C (34-34F more or less).

@0soyoung i've seen you post a few times about this, and I am anxiously waiting for your opinion/knowledge on whether spring bleeding affects the tree? So many experts say no, but it is a loss of energy after all? is the energy simply lost of areas that don't matter (the wood/xylem)? Sorry to put you on the spot with the question -- i'm sure a lot of people here value your knowledge (and generosity when sharing it) as much as i do

Yes, you are correct, sugar is antifreeze in trees. What matters to the cold hardiness is the fluids inside living cells, not so much the water in xylem lumens. Ice crystals will puncture the cell membrane and death of the cell will follow. The xylem lumens are the just cellulose wall remnants of cells that have been emptied. It is relatively unimportant whether water in a lumes freezes or not. Freezing can only lead to cavitation in the water column. This would mean the lumen is no longer useful and may be sealed off or possibly it gets refilled though 'leakage' from other lumens. This is important for alpine species; not so much for Japanese maples.

I am in the 'so what' camp regarding bleeding. The advice to overwinter above freezing is interesting. Bleeding happens because a 'stem pressure' is created - sugars are dumped into the lumens; additional water moves in by osmosis, creating the pressure (btw, hence why root pruning dissipates the rate of bleeding). Relieving the pressure only drains some of the sugar water - the same sugar concentration would exist in the remnants. So, the 'keep above freezing' advice rests on the belief that bleeding continues until the sugar is purged from the entire xylem column. I don't think so, but maybe .... .

 

[Paulpash]

The bleeding isn't important - it won't ruin your tree but dieback can really mess up your plans.

Nothing is foolproof in maples when it comes to big cuts - the smaller the chop the less probability that the Acer will 'over compartmentalize' as a result.

Two strategies, in my experience, will help:

1. Cut in stages. A chop or big branch removal does not have to be done all at once. Cut through halfway from the top. Next season cut a little more from the backside. Complete it the following season. Look up Ebihara trunk chop.

2. Play 'join the dots' . When you cut, try and always make sure you have as many branches, stems, buds as close to and around the chop point as possible, especially the bottom of the chop. These branches are more likely to 'ring fence' the compartmentalization and stop it escaping down the trunk. This is not a guarantee, as can be seen from @0soyoung 's maple after he chopped it after the layer but it is far better than ending the cut at a bare point on the trunk.

I believe this is why good maple bonsai are among the most expensive material for Bonsai. The potential for ruining a tree through chopping is quite high.

 

[River's Edge]

The bleeding isn't important - it won't ruin your tree but dieback can really mess up your plans.

Nothing is foolproof in maples when it comes to big cuts - the smaller the chop the less probability that the Acer will 'over compartmentalize' as a result.

Two strategies, in my experience, will help:

1. Cut in stages. A chop or big branch removal does not have to be done all at once. Cut through halfway from the top. Next season cut a little more from the backside. Complete it the following season. Look up Ebihara trunk chop.

2. Play 'join the dots' . When you cut, try and always make sure you have as many branches, stems, buds as close to and around the chop point as possible, especially the bottom of the chop. These branches are more likely to 'ring fence' the compartmentalization and stop it escaping down the trunk. This is not a guarantee, as can be seen from @0soyoung 's maple after he chopped it after the layer but it is far better than ending the cut at a bare point on the trunk.

I believe this is why good maple bonsai are among the most expensive material for Bonsai. The potential for ruining a tree through chopping is quite high.

Critical points
When i asked for an explanation on chopping back maples to create taper from a noted maple grower in Japan. His explanation included both points, You can cut back in stages it does not have to be at once. And the more lower branches you can retain to help heal the staged cuts the better. This also works very well in developing conifers.
I had asked what was the best time to cut back for a chop and his explanation included multiple options at various times based on condition, size and time of year. All variables that determined how much and when to cut. I was surprised when he stated that one can cutback at several times throughout the year in stages. I now know that this process was essential in balancing the growth, node length and taper.
For example if one is facing very vigorous growth it could be important to shorten the extension early in the season to slow the progress.

 

[Adair M]

The bleeding isn't important - it won't ruin your tree but dieback can really mess up your plans.

Nothing is foolproof in maples when it comes to big cuts - the smaller the chop the less probability that the Acer will 'over compartmentalize' as a result.

Two strategies, in my experience, will help:

1. Cut in stages. A chop or big branch removal does not have to be done all at once. Cut through halfway from the top. Next season cut a little more from the backside. Complete it the following season. Look up Ebihara trunk chop.

2. Play 'join the dots' . When you cut, try and always make sure you have as many branches, stems, buds as close to and around the chop point as possible, especially the bottom of the chop. These branches are more likely to 'ring fence' the compartmentalization and stop it escaping down the trunk. This is not a guarantee, as can be seen from @0soyoung 's maple after he chopped it after the layer but it is far better than ending the cut at a bare point on the trunk.

I believe this is why good maple bonsai are among the most expensive material for Bonsai. The potential for ruining a tree through chopping is quite high.

Good maple bonsai are expensive because it takes a long time, even with the most advanced techniques, to do it “right”. By “right”, I mean there are no large wounds, all wounds that happened are closed, and mature, the trunk and all branches have taper, subtle curves, good structure, no or minimal wire scars, good ramification, good nebari, and evident age.

 

[Japonicus]

Last year I trunk chopped a maple in February or early March.
It never leafed out...This one will have buds below the chop, at least.

Was this a Japanese maple and were there some branches on your trunk below the drastic prune?
I just did a drastic prune and 75% or more root removal on a Japanese maple with no bleeding.
Buds are showing some signs of plumping. Hope it takes and my 1st ground layer by tourniquet is successful.

So i ran all of this by a local here in Montreal who has VERY successfully been growing and showing Maples for 30-40 years.

He, without fault, keeps all maples at a steady +2-5C (35-41F) all winter.

Pruning:
-Trees in trunk development stages are pruned when the leaves have fallen off.
-Trees in refinement are prune at bud swell (untouched in fall)

Chops:
-Trees in trunk development stages are chopped at bud swell in the spring.
-Trees in refinement that require big prunes/chops, are done at bud swell.

Based on his experience (and the many others i have spoken to) bleeding does not have any noticeable negative effects.

Repotting (including heavy root work):
-Trees in trunk development stages are repotted at ANY time during dormancy (November to mid-March).
-Trees in refinement are repotted at ANY time during dormancy (November to mid-March).

Crucial: if his dormancy temperature drops below 0C (32F), he does not touch the trees at all until bud swell, or after first flush.

Now I find this information! Many thanks for this break down and info both to you and @Mike Hennigan for the compartmentalization explanation. Ososcientific Good one.

 

[Cable]

Was this a Japanese maple and were there some branches on your trunk below the drastic prune?
I just did a drastic prune and 75% or more root removal on a Japanese maple with no bleeding.
Buds are showing some signs of plumping. Hope it takes and my 1st ground layer by tourniquet is successful.

Yes, it was a Japanese maple and no there were no buds below the chop.

This year I kept my two remaining JMs in my root cellar which hovers between 35-40 degrees.

 

[Japonicus]

Yes, it was a Japanese maple and no there were no buds below the chop.

This year I kept my two remaining JMs in my root cellar which hovers between 35-40 degrees.

Nice! you’ve got a lot working for you having the cellar

 

[Cable]

Hopefully. It is my first year using it (it came with the house when I bought it but hasn't been used in decades). I put a table in there with metal legs then put glue traps on all four corners and two more in the middle in an attempt to guard against mice. I have my two JMs, a chinese elm, and my trident seedlings down there. I also recently added a boxwood and a juniper (used for a demo) that were removed early from winter storage so I didn't want to let them freeze.

 

[clem]

Japanese Maples have a few particular characteristics that are unique to them.

There is a window of time in the fall to trim and cutback with no “bleeding”. And that period is just after the leaves have reached peak color. For about two weeks. So, the best practice is to remove the leaves, (yes, I know... they’re still pretty!) and cut back to a bud that’s facing the direction you want the branch to grow next spring. Seal the cuts. If, when you make the cut the tree bleeds excessively, stop, and wait a week.

The reason this works is the tree is pulling the sugars out of the leaves, so the flow is away from the tips. The tree shouldn’t bleed.

Another method, more useful in the spring, is to repot when you cut back. Removing the root tips prevents the tree from quickly absorbing water to bleed.

One more: you can prevent bleeding by running a sycle along the inside edges of the pot. This damages the roots just enough to prevent bleeding when cutting back.

Pruning from june to october is safe in my little experience : no sap withdraw, no sap bleeding.

 

[AlainK]

I think it's been said before, but :

1/ pruning the top and the roots will reduce the bleeding.
So it's safe to repot and prune the tree at the same time - providing that the tree is kept frost-free. Anyway, bleeding doesn't harm the tree since that what bleeds is essentially natural "anti-freeze".

2/ pruning in the growing season allows the cuts to heal faster, so early June is a good slot too.

If you prune in autumn, especially if you do some "hard" pruning, it's likely that dormant buds will grow. Depending on what you want to achieve, it's either a blessing - or a curse : many buds in a small area can cause some swelling, even if you remove them early.

 

[JohnDoses]

Sifu, I think something that will help you understand this concept is identifying the difference between “healing” a scar for aesthetic purposes (where the bark grows over exposed wood) and how a tree compartmentalizes a wound inside of the wood.

Compartmentalization and the concept of CODIT, which @0soyoung mentioned 0soscientifically, is what is important to understanding the timing of big chops. NOT the aesthetic “healing” of bark over exposed wood, which can take years to accomplish.

Compartmentalization happens much quicker and it is the process that will protect your tree from disease entering the tree. In lamens terms, it’s as if the tree is forming a protective wall INSIDE the wood, to block out pathogens and protect the wood.

Now, compartmentalization cannot happen quickly enough to protect the tree from disease, desiccation, and dieback if the chop is made while the tree is dormant for too long. So, it is not the healing of scars which takes a long time that matters here. That is always an afterthought that can be dealt with later, after the tree has had the opportunity to compartmentalize any dead wood that results from a chop.

This is why you always hear people say that when pruning a deciduous branch off of a tree... to always cut outside the “shoulder” of the branch. It is easier for a tree to quickly compartmentalize the wood at the shoulder. If you prune past the shoulder into the trunk, the tree will struggle to compartmentalize and you risk a greater wound or die back down the trunk.

To illustrate this concept, here is a picture of a trunk on an American hornbeam clump that I collected. This trunk experienced dieback on the side where there was no branch to keep sapflow going when I made the initial trunk chop at the time of collection in the early spring. I cut the trunk back to the top branch and you can clearly see where the compartmentalizion of wood occurred. Fortunately I have more branches below this point where the trunk is still fully alive that I will cut back to eventually.

View attachment 217217
View attachment 217223

The red line shows where the tree “walled off” the ‘dead’ wood (blue) to protect the ‘living’ or viable wood (green). That is Compartmentalization, that is occurring inside the wood of your tree anytime you make a pruning decision, and that is why the timing of your pruning matters. You want to prune at a time when the tree is NOT fully dormant so that it has the ability to compartmentalize. Don’t think about healing scars, because that comes later. While it may take years to “heal” a scar, the tree compartmentalizes very quickly in comparison. And that is what will protect your tree from disease, etc.

View attachment 217217View attachment 217223

Awesome post and great info, thanks!

 

[my nellie]

I would like to ask a question but at the same time to say a Big Thanks for all the valuable information contained here in this thread.
My question is : In which occasion (if any) could a JM be safely chopped during the active growing season to a point where there are not any lower shoots/branches on the trunk?
Thank you in advance.

 

[Deleted member 21616]

safely

never

 

[my nellie]

That's the expected response @derek7745 Thank you