Elms for USDA zone 5 and zone 4 - these species should be able to be wintered, outdoors, without temperature protection, pot set on ground, protected from wind & maybe sun, mulching in optional.
The elms that stayed outside in winter are now pushing new growth and any leaves from last year will slowly (or faster) drop as the new growth comes in. I get this every year on mine.
Here in NC, they drop, but later than just about all my other deciduous. Even today (Dec 5) I'd say only about half of my Chinese elm leaves have fallen off the trees. Compare that to my American elms, winged elms, cedar elms, silver elms, English elms - all of which dropped a month or more ago.
Siberian elms are pretty vigorous trees and like most elms, they can take dramatic root reduction (like 95 percent) at the right time. Also your location dictates what you can do with them right now. If you're in an area that is winter now, working roots, trunk reduction etc. is not in the cards until early spring arrives.
I saw many YouTube (maybe it's magic of YouTube), where chinese elms after such pruning reacted with few centimeters of growth from everywhere after a month. Overall i think it's healthy, but a little stagnant. I have also searched for aphids and spider mites with my eyes and white paper test from Bonsai Mirai video, everything seems clean of ...
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