Bill Valavanis tends to grow his trees in pots, rather than growing them in the ground. This gives him better control over the nebari.
There is also the theory that they develop aged looking bark faster when grown in a pot.
Kimura, if he wants to develop the bark, will shade it. He noticed that trees in the ground have rougher bark on the north (the shaded) side than the other sides. So, he will turn a tree to shade one side if he wants that side rougher. Or, construct something to shade the entire trunk.
So, since Bill growers his tree in pots, he rotates them. So, all sides of the trunk gets shade from time to time. Thus, rougher trunks.