This may be a dumb question but what else would you expect from me? I just got a couple of smaller trees from Andy Smith – a ponderosa and a RMJ. Both are 30+ years old and of course high elevation yamadori. My question is: will these trees grow in trunk/general mass size or just foliage? On one hand, they’ve had decades to get big and nature has said “no way – you stay small.” On the other, they’ve lived in harsh conditions during those decades and now will be given a pampered lifestyle with fertilization, protection, careful pruning and watchful eyes. Do yamadori like these trees tend to recover growth ability or can I expect them to essentially stay this size during my lifetime of being their caretaker?
A tree grows to it's full potential in nature because of ideal conditions and unchecked root growth. Good yamadori found in nature is close to being bonsai because of the reverse. Harsh growing conditions and a root system that is minimized generally due to rocky conditions and lack of real soil.
Putting a tree in a pot is mimicking the same conditions for which Andy gathered this tree. Minimal roots, minimal tree. You are right in thinking that because of the better environment of our well-watered, well fertilized, non-violent back yard, that they will be more productive. Not so productive that the girth of the trunk will see much change(that's why people talk about putting trees in the ground or grow boxes). The growth of a trunk at the base has more to do with unchecked root growth. Putting it in a pot slows that potential down drastically.
The foliage and it's design is another matter. Thus the three phases of bonsai development...1. trunk, 2. branch placement, 3. ramification.
After your trunk is the girth you want with good taper, then you have to move to design...getting branches where they look best. Trees will grow and design will get a way from you if you don't keep up on it. So the answer to your question of growth ability is yes they can get stronger, but they can also get weaker when people mess with their trees too much. That part is a multi-faceted question.
Do answer your last question... you can expect the trunk you have to keep the same dimension for all of your days(growth but minimal). If you do a good job of getting the tree to a point of good health, it will grow and see a lot of change in your lifetime and it is a constant job of keeping growth near the trunk and fighting the extension that is one of the battles of bonsai.
