Your Chinese Elms can stay outside year round in Kentucky (and probably should). In my zone, they are semi-deciduous and they often do not drop their leaves until the spring as new leaves push out. However, I once moved across the city and for some unforseen reason, it dropped all of its leaves. A few weeks later all the leaves were replaced. I probably couldn't kill the tree if i tried. It was still producing leaves as of last december and i live in Atlanta. This tree is the most vigorously growing in my collection and I have about three of them. Prune them back as often as you like as they grow fast. Use a combination of wiring and directional pruning, but check your wires often.
This link might help you:
http://www.bonsai-bci.com/species/elm.html