Because it's so important to develop a trunk without scars, it's best to build trunks one section at a time...once the nebari is established.
Let a trunk run long, then chop it low, and so the scar is toward the back, and let the next section grow long enough to help close the scar in the section below. Ideally, this results in taper and some movement. This sacrifice growth should be grown with the sole purpose of thickening the next section of trunk, and virtually nothing else; other than a few small shoots that are kept small but alive, on the outside of the curves.
I did a bad job with this one,; the chops are mostly hidden, and you can see 5 distinct trunk sections, with small shoots retained at the outside of curves. Ideally, however, these would be progressively smaller in length and girth as the trunk ascends. The second section blew it. Now I'm trying to find a front that doesn't necessitate cutting it off at the second section and spending another 10 years in the ground:
If you allow sacrifice branches to remain on the section of trunk you're trying to develop, you get a bulge:
That necessitates a cut that becomes visible from 90 degrees or more of the tree; reducing my options for a clean front. See the scar front & center on the first photo? It's 6 years old, and has been in the ground "healing at an accelerated rate" for 5 of those years. How long until that's healed up in a pot? 10-12? A long time!
This is a great example of why it's tough to get good results from just sticking a tree in the ground; even after getting the nebari right. It requires a lot of planning ahead, understanding how a tree is likely to respond to chops, and having a vision of how the finished trunk should look. My first quince above is great until halfway up the second section, but since I failed to chop low enough, I have some tough decisions or compromises to make.
Finally, envisioning good perspective and scale are tough in the ground. Unless you're laying prone on the ground, the perspective is from above and not straight on as we tend to view bonsai in pots. And scale is distorted to the larger. Let a trunk grow to 10' tall, it seems wasteful or too drastic to cut it down too far, when the reality is, a trunk should have movement really low if it has it at all. Tough to get the potted tree's scale right when it's in the ground, but keeping 4" of a 10' tree will make a more interesting bonsai later.
