Interesting. I have never re-potted my tropicals at any other time than winter here in zone 5-6 Michigan....unless I had to.
I am interested to know why others do not, as I said, I have had no ill effects, no deaths, and no serious decline in growth by doing so. My tropicals do not stop growing in the winter, pinching back is a constant chore all year long, some times more intensive than others....the response from the trees after winter re-potting has always been great.
I have posted some of my tropicals here on this forum, I think it is easy to see that they are healthy and vigorus and that they do not seem to mind winter re-potting at all.
Of course, since I have only been doing this for three years...maybe there are some long ternm effects others have experienced? I would like to hear the reasoning against re-potting in winter, if the conditions are favorable, of course.
You mention in your post zone 5, but I see zone 6 in your personals. Where do you live.
I live in NE Ohio, zone 5 and have MANY tropicals which I overwinter in the house under lights or in windows or both.
I never repot in winter unless I have too. I'll get to that in a minute.
I repot tropicals when it is hottest and most humid here, late May through August and into early Sept. if I have too.
HAVE TOO! = Root rot problems or potential root rot probs. If you have acquired a tropical that is in the heavy, goopy, always-wet soil that they often come in from , say, Florida, then I would repot before winter paying attention to minimal rootage removal. I feel that it is MORE detrimental to leave them in this soil for overwintering indoors than it is to repot.
If your tree(s) aare already in a good bonsai soil, and no signs of root rot probs then I would recommend repotting them in mid-summer here and they will respond quickly.
Also, one great thing about having tropicals in the north is that I (We) can do the worst stuff to them during a season when we can't extensively work on our hardy trees.
Here's an opportunity to put something to the test. Since you treat all your tropicals the same way, you don't know for sure that what you are doing is most advantageous. I would suggest repotting one or two as Dale suggested for the next couple of times and checking the results.