Deciduous Dends?

[reinbo15]

I have two Dendrobiums that I don't know how to handle for the winter. One is Dend pierardii and one is Dend superbum, and I read that they are both deciduous. How do they know when it is winter? Are they photoperiodic? These little guys are just seedlings, so I was wondering if I should be giving them a winter rest this year. If so, when do I start? Any advice or information for a newbie with the deciduous types is very welcome. I opted to try with the seedlings first so that if I messed it up, it wasn't an expensive loss.

Thank you!
Lisa