When to trunk chop maples?

[tgooboon]

When is the best time of year to trunk chop this japanese maple?
The trunk is approx 1cm. And would you cut after the first or second node?
Would you cut the branch back at the same t i me or later?

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[shibui]

I cut back Japanese maple almost any time of year. I try to avoid early spring as they are prone to bleed a lot at that time of year.
Late spring is a good time because they are ready to grow so new shoots get started pretty quick.

I assume the branch you mention is the smaller trunk right down low on the right of the photo? It probably won't matter. I would leave it for the moment simply because it will keep sap flowing through the trunk and possibly reduce the chance and extent of dieback around the cut.
There is quite a few more years of development in this tree before it can be called bonsai.

[tgooboon]

So would you think I should keep growing for thickness and cut at 2-3 cm or cut now then keep growing with more movement
Trying to avoid massive scar and get movement

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[shibui]

What do you want? Every bonsai is different so the development will vary too. How to proceed depends on how large a bonsai you plan for. It also depends on what style (tree shape) you want.
I do not let my grow trees just grow with one thick trunk then cut. That leaves one huge scar. It will take many years for that to heal. It also takes a long time for the new leader to catch up and blend with the thick stump.
The way I develop trunks for informal upright trees is more frequent pruning so the trunk is developed in many smaller steps rather than one single huge cut. Your tree is probably ready for the initial cut. You should make the first cut around 1/3 of the final height of the bonsai so you will need to have some sort of plan for how big the bonsai will be in the end. Don't worry if you don't have a firm plan. There is plenty of latitude to change and refine the plan as you go along.
After the initial prune you should get 3 or 4 new shoots take off. Let them all grow all summer. If they get big enough they can be cut back for the second step next winter or spring. JM can be a bit slower to grow so if they don't get big enough leave them for a second year then do the second stage cuts which will be a couple of nodes above the initial cut.

All the new shoots will increase trunk thickness at the base. The changes of angle where new shoots started usually give the trunk some movement and character. Each new growth will be a little thinner than the previous bit so the trunk will also have precious taper. The subsequent growth helps heal the previous cuts so in the end you should have a trunk with just a few smaller cuts to heal up. As the trunk develops I remove the bits that look out of place. In the end there will be just a single line of trunk with fewer scars, plenty of curves and bends an good taper.

[tgooboon]

I cut it off, slightly under a cm at this point.

This japanese maple grows very differently to my trident maples. What is now the truck was only a bud 6 months ago and it took off and left the weak trunk behind (now a small second trunk/branch.

I will keep cutting back the shoots a little before they get this thick.

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[shibui]

This japanese maple grows very differently to my trident maples. What is now the truck was only a bud 6 months ago and it took off and left the weak trunk behind (now a small second trunk/branch.

Don't accept a single event as a general rule. Not all JM grow that way and the same thing happens occasionally with other species, including tridents, as well. I guess it has something to do with a shoot or branch not being strong enough, maybe some damage we can't see, so the plant grows a replacement.
As mentioned earlier it depends what you are aiming for but 1cm thick cuts sounds like a good size to me. With luck you should get a few new ones grow. If they all grow well you could expect the lower trunk to double in thickness this year and the new ones to reach around 1cm each. Next year's pruning would then consist of picking the best line and shortening it back to about 1/2 the length of the lower part then cutting all the others right off close to the trunk. You can rinse and repeat as often as you like until the trunk reaches the desired thickness or height or both then get it in a grow box to slow the growth while branches develop.
Good luck on the journey.