When is the best time to transplant bamboo?
I am talking about areas which have severe winters,
such as Colorado or New York.
Spring or Fall?
Thanks.

Plants are more sensitive to temperature when not yet established, so doing it in autumn in an area with a severe winter seems like an unnecessary risk; also you won't get much progress towards establishment when it is too cold for growth. Here in mild southern Britain, I like to do it in autumn because I can get some useful progress towards establishment during the 6 months or so before they send up culms in spring.