Was trying to post in Maples but HOUZZ somehow gave only limited options.

Bumping.

I did just find Al’s thread on potting up vs re- potting- very helpful maybe that’s most of the answer. Perhaps if any major encircling roots these would be untangled mainly to allow potting medium to fill in. But may not matter as much since those would not be major feeders.

I had thought that potting up would provide more growing medium for watering & make the small trees a bit more resilient during the hot summer, but that was when assumed the roots would automatically be “ happier “ when potted up.

Sorry I missed this discussion earlier and I'm not sure if I am really answering your question but I grow ALL my JM's in containers and when I buy a new one - almost always in leaf - I just pot up. No bare rooting, no root pruning. But I buy small, JM's here are most often grown in a very barky planting media anyway and I have yet to find one that had root issues serious enough to warrant bare rooting and correcting before planting up. And I do use a mix very similar to the 5-1-1, so again, very barky.

But I have not grown any from seed intentionally so I can't address how that approach may be different or the impact that may have on the root system compared to store bought trees growing a very durable growers' mix :-)

I should also tell you that seed grown Japanese maples can never be referred to by a cultivar name. Reproduction of all the attributes of a named cultivar, in this case Sango Kaku, can ONLY be achieved by asexual propagation - grafting or cuttings. Seed grown trees are just considered the straight species of Acer palmatum regardless of their source and may or may not resemble the parent tree very closely once they mature. So what you are growing may look like Sango Kaku but technically it is not. It could also grow up to look nothing like SK.

Thanks. gardengal, that is helpful. I will just pot up a few into 5:1:1 without messing with the roots really.

They came from trees I planted on another property 20 years ago, where I also had a lovely Viridis and container JM’s also, ( here I have a Full Moon, Crimson Queen , and Shishigashira in containers, but not in 5:1:1 yet), so there’s also that sentimental clinging to plants related to a former garden, and growing “ my babies”. And I have planted a number of things I managed to bring over.