I have two plants that I bought as Mandevilla. They are similar, but not the same. This will be the third winter for one. I have an unheated porch with a glass front facing east and I hang it in there. Last winter I did cut it back because the porch is narrow and crammed with plants in the winter months. I didn't cut it back anymore than I needed, so I wouldn't call it a severe haircut. It's growing as a hanging basket, so it was cut just enough to give me air space. The new one is grown in a container but on a fixed trellis outside. It will have to be cut off more drastically just to free it from the trellis. The plan is to see if I can overwinter it in the garage under low light conditions and hope it regrows next spring when I can take it back outside.
