In fall you see a big movement of nutrients etc from the tree towards the roots in many species, which would aid the tree in the recovery. I think a lot depends on local climate. Hot dry regions might be less sucessfull.

leatherback wrote: In fall you see a big movement of nutrients etc from the tree towards the roots in many species, which would aid the tree in the recovery. I think a lot depends on local climate. Hot dry regions might be less sucessfull.

Good point. But then for example, when do they repot JRP and JBP in Japan?

Climate I have here is not as humid and hot as the one they have there, but it's not too far either...

This is what I did to my mugo on Aug. 17th


I do not know when they repot in Japan. My climate is so much different from Japan that for me it is also less relevant.

Decided to be bold and repotted tonite.
Managed to fit all the roots in the new pot without cutting anything, and moved as much of the mycorrhiza as I could as well. So I wouldn’t expect anything bad as result.

Actually, it would have probably been worse if I waited next spring, as given how much the roots had grown in the grow box, they probably wouldn’t have fit he pot if they kept growing for the rest of the season...

BofhSkull wrote: Actually, it would have probably been worse if I waited next spring, as given how much the roots had grown in the grow box, they probably wouldn’t have fit he pot if they kept growing for the rest of the season...

No.
That's ONE of the reasons we should trim the roots when repotting, to fit into the new pot.
But...
There are many other reasons; to induce growth and ramification of the roots, to get rid of tap roots, to cut thick downways roots, ugly roots and/ or dead roots.
So you didn't wait, which is fine, but if the tree is healthy, it will continue growing the roots the same way it would grow in the grow box, and...
Your pot will be root bound in no time.
So I guess it is always better to trim (or prune) the roots when repotting.
My two cents, sorry.

I don’t disagree. What I meant to say is that if the concern (mine) was about this repotting being stressful to the plant, this one should be as stressless as it can be, and one done in spring would have been worse.

I’m not too concerned about it getting root-bound particularly quickly: it should be able to grow for a couple of seasons in this pot with no problem, in terms of density. But since the grow box was significantly bigger than the pot, the roots would have probably become too long to be repotted without cutting...