I cut mine back after they stop blooming or when you take them inside. They are usually like magnets for mealy bug so you had better spray it really good after to take it inside to be sure your other plants do not get them. I really cut mine back hard because they go into the greenhouse and take over if I do not. They are like weeds and love lots of water and sunshine.
The one shows you how far back I cut them. They are still blooming in the greenhouse today, Dec. 1st. thurd picture.

JB, it is beautiful you must be very proud.

I agree! I had one once, and somehow managed to kill it. Your pics are inspiring me to try again.

I am worried about these plants now. The temp in the greenhouse goes below freezing these nights and back up to normal in the daytime when the sun is out. These plants can't take that cold. It was 30 deg. in the Greenhouse again last night. My SIL wanted to go check and I told him to just let them go and keep the door closed. Two heaters working so hard as is, so we can only pray for warmer weather. I will send pictures when I decide to look in on them.

I hope your plants are ok in there JB. We have a heater in ours, but our lowest has been 16 outside and 55 inside with the heat going full blast. We'll have quite a bill but the plants are all doing well so far.

Same here Karen .. going to be an epic electric bill soon .. I have two space heaters in my greenhouse and thankfully no power outages. It hasn't gotten below 54° in there even with temperatures in the teens!

Jacquie for those tender tropicals before I got heat for the greenhouse I used to put them on 2ltr bottles painted black with water in them. In the daytime they collect heat and release it at night. Won't really help the bits above ground but definitely keeps the roots from freezing.

The three red mandevilla are still alive. The one heater had to be replaced. We had a water break in the greenhouse right next to the heater and that is when we realized the heater was not working 100%, Fortunately the weather has gone above freezing and the sun keeps them good and warm during the day. We watered today for the first time since the break was repaired and everything was really dry but alive. We will see what the next few days bring. I am going to do some heavy pruning this week if I feel up to it. This weather has been tough on my old arthritis.

I'm so glad your three red mandevillas are fine! They are so beautiful! I had one and managed to kill it when we went on a 2 week vacation and it didn't get watered. I'll have to get another one. I do love them!

Take it easy. I know how hard it is to do what you want to do when you have bad arthritis. Things still get done around here, but I'm so much slower than I used to be.