IMO the window is still open for a few more weeks, as the canopy has just opened and root development is about to begin. Have a look at the roots and make the decision. A couple I repotted last week were fine, no soft new white roots showing, just woody and old roots visible. Just don't do anything too overly drastic at this time of year!
imo, definitely no root pruning when the tree is in its active growth cycle. Best time is January thru mid March A lot of unwanted stress on the tree will likely occur
It would be interesting to know whether you prepare the plant at all in advance of repotting e.g. increase watering in the week or weeks running up to repotting.. I don’t, but logic tells me this would be a good idea.. interested to know what others do if anything
I think I already posted about this -always potted- 'Atropurpureum dissectum' (no tag when I bought it some 20 years ago), but I tried several key-words in the search box and couldn't find the initial post. Anyway, here's a summary : It got a pretty bad dark spot in 2013, so I removed the damaged part until I could see the cambium. I then painted the naked part with Bordeaux mix, and added a thin string of Japanese bonsai cut paste on the live edges. It took about 3 years to heal completely : But the pot was very heavy, and because of my back problems, I couldn't repot it when I should have. In March, before budbreak, I finally managed to take it from the pot by pruning the roots that were clogging the holes in the pot with a concave knob-cutter (bonsai tool). Water ran out of the pot ! Baaad... I trimmed the roots and repotted it. At the end of April, I thought it was dead, so I cut all the branches, I just left the trunk : But at the beginning of May, I saw some dormant buds showing : Even some are popping out almost to the top. Yesterday : My latin teacher used to tell us "Nolite itaque amittere spem !" : it could be the motto for someone who has a passion for trees...
