I did a fun experiment over the winter where as a complete noob decided to try his luck with leaving these outside all winter, not really knowing what the hell I was doing. Well one made it, the other didn't. Funny enough the rough bark Chinese Elm was the one that pulled through (I'm definitely okay with this). Next year I'll have to provide more protection during freezing temps and snow. Now this is by no means a controlled experiment where I can say that rough bark variety is more cold tolerant, but it SEEMED to be the case here. Both were on same watering schedule, location, and pot types. Either way, I love Chinese elms and they are some of the most forgiving and hardy trees, just maybe don't leave them in sub freezing temps.