I bring mine in and put it in the cellar along with my brugs. Once a month I water it and check for bugs.

We had a Mandevilla a few years ago. Very pretty vine and flowers. Gave it to my sil 'cause we wanted something different in the pot. We over wintered the vine in our front parlor. When the cool days started we brought it indoors. We trimmed back the vine to keep it manageable. Put it in a south facing window. With the exception of an occasional watering we left it alone. It will loose its' leaves and look pretty bad but come the warm weather next year it was fine and grew and flowered. NancyLouise

As the prior posts indicate you can either set it in a sunny window, or just let it sit in a cool cellar or garage, that doesn't go below freezing. In either case you should cut it back befor bringing it in. My understanding is, and I failed on my only attempt, mandevilla have a less than 50% survival rate here in the northeast. I purchase a new Mandevilla or two every spring and discard it in the fall, not very economical but that's what I do.

We cut 2 back and put one in the basement and one in a sunny window on the 2nd floor and only the one on the 2nd floor lived over the winter. The one in the basement went dormant and never re-emerged.

I keep one in the basement under flourescent lights with other tropicals. It loses a lot of leaves but has survived about 3-4 years this way. It is blooming nicely right now.

I don't know how much longer this will work. Its in a pretty big pot right now. I think I may have to root prune it this fall when I bring it in to keep the pot size manageable.

I transition my tropicals in the garage in front of a window in Sept (October?) when the nights get cool (