AusBonsai

I've had this JM for a couple of years, which I received as a gift. It was the victim of some marauding possums (repeatedly) last year, and I've never felt it was ready for me to do anything, really. I need to thin out the top, no matter what else I do, and will put it into a bigger growing pot this year.

I'd be interested to know what others think: should I chop it? Or just sit back and see how it goes after a few years of free growth?

It might work as a formal upright maple: the trunk is dead straight, but it has some nice lower branches. I usually think of formal upright as being a bit boring...

Or would others I chop it (at the level indicated: air layer then chop) and introduce some movement?

I would put it in the ground or bigger pot and let it go for a couple of years.

The choices are 6 of one and half a dozen of the other.
If I was growing a formal upright JM I would not be bending branches down and definitely not straight like they are now. I prefer the more natural look of branches that grow up and out for JM styling. I would still probably chop that trunk, even for an upright tree. Straight is one thing but no taper is quite another thing for any bonsai.

Chop to create movement is always an option but it will probably add years to the project and there is never any guarantee that the result will be any better than before. I would always check the rootage before deciding to go informal. If all the roots are on a level plane it will be difficult to tilt the trunk sideways to get a good initial trunk angle. Informal upright with the initial trunk vertical never looks good There could be options to trim off some roots to get a good trunk tilt but we can't assess that from the photos so you will have to make that call.

In most cases it is quicker and the results better by choosing a tree that suits informal upright rather than converting a straight trunk.

Letting it grow after a chop is always a good idea. Helps to heal the cuts as well as adding some girth to the trunk.

Really appreciate the comments. Will see how it goes!

If it's your only bonsai I would thin the top as you say and develop it as formal upright as is. Enjoy it for what it is and learn from it. If you have others, plant it up (preferably ground) and let it go nuts. I have my first JM, also formal upright. It is still not much but I won't give up on it.

I have had my best results with maples when I continually cut to the shortest possible internode. If this were my tree I would probably chop the trunk just above the lowest branch(es). (In one photo it looks like there are two low branches.) And, as Shibui indicates, wire or let them grow naturally upwards. Shortening the trunk and letting the lowest branch(es) grow unchecked for a season or two will give you a new leader/apex and go a long way to overcoming the lack of taper. IMO, this would give the tree a good chance of taking on a natural look. I'll be interested to see what you decide to do.

I think my advice would be for you to think over the following.

A) have you got a planned size for the future tree to be? Will it remain in this pot? I know from experience not everyone has garden space to plant trees out to grow faster, not sometimes the inclination to do so.I for the first year or so just enjoyed young trees in pots because I just liked the autumn colours, not because I was trying to actually achieve a goal with the trees.

B) if you do cut it hard back, are you willing to spend the years regrowing it it back? In satisfaction terms you may actually get more enjoyment out of the straight trunk that looks like a tree than the regrowing shoots to try to make a trunk all over again. Or you might love the process of shaping it how you like, only you know.

A hard cut is a commitment to regrowing for years so an idea of what you like about it, and what you might want to achieve is best considered prior to the cut

Thanks for all the feedback!

I like this tree's spring colours, and hope to keep it, but there's clearly a long way to go before it'll be a bonsai. I'm in no hurry - our place has a miniscule backyard and we hope to move in 3-4 years to somewhere with more room, so whatever aspirations I have are in the longer term. Luckily, we get enough sunlight to grow things in the meantime.

I've thinned out the apex, leaving one longer leader, and have moved the tree into a larger pot.
The roots were quite symmetrical, but there's a tiny slant I exploited when replanting. I might try shaving off roots to change the initial trunk angle next year - that's an interesting suggestion that hadn't occurred to me at all.
I plan to make a low cut, but will probably wait to make sure it's still happy after the recent relocation and might try to airlayer it. There are some lower branches, as Phil pointed out, which will hopefully go gangbusters if I leave them to grow freely.

For what it's worth, the photo (a Trident, not a Japanese maple) shows how you can develop ramification by cutting maples quite hard to the shortest internode. If you feed well, you can cut like this after every growing season. So in just a few years you will have a nice structure ready for refinement.

On Monday I separated a successful (if sloppy) air layer for this maple.
It has looked much more vigorous this year after moving to a fast draining soil (about 25% akadama, 25% scoria, 50% Debco terracotta mix). My wife has named it Santos-Jebediah. I do not know why.

After apex thinned and leafing out:
Air layer applied (September 8):
I tried to be too fancy for what was my second ever air layer, by trying to keep too many branches above and below the layer. This led to much of the sphagnum sagging down and a lopsided moss distribution. Much electrical tape was used to reinforce the structure.
At about 1 month the moss appeared dry and I injected about 3ml of water mixed with a little root hormone via a syringe and needle.

After about 2 months (November 15) I checked the layer:
You can see how the new roots hang down quite a bit. I had to reach up under their veil to cut off the base of the graft.
There's obviously still a long way to go in developing these, but I'm much happier that I have a direction now.

I'm more interested in the top half ('Santos') of the graft at the moment, which I think has better potential in terms of initial movement and low branches. The layer was cut diagonally, to allow for an initial trunk angle, but I'll have to wait for next spring's repotting to see how well that turned out. It needs a few years to grow out those ugly knots, but I hope to ultimately keep it shohin-sized.

I'll let the bottom half ('Jebediah') run rampant for the rest of this year. I expect to remove a bit more of the trunk (possibly as far as the first branch) in late autumn for better taper, but would be interested in others' thoughts.
I will keep this thread running if there's any progression worth noting from here.