Keeping Dipladenia outdoors in winter

Question

I live in Port Chester, NY 10573 I know that leaving the plants
out during the winter would kill them. They are currently all planted in large pots
I would like to know your opinion on the following procedure;
1. Put them up against the house that faces South. This will give more
exposure to the sun and shield them from the wind and snow.
2. Trim them and cover with 55 gal. black plastic garbage bags.

Please get back to me and let me know. If you find the above works
I will plan on planting more of them next spring.

Thanks in advance,
Anthony Treglia
14 Davenport Ave
Port Chester, NY 10573
[e-mail]

Answer 1

I don't think this will work. Mandevilla is fully hardy in zone 9 and warmer. You might be able to coax a plant hardy in zone 7 through a NY winter but even that is iffy. One issue is being in a container and therefore having the entire rootball subject to air temps. All plants in containers should be treated as though they are in one zone colder than your actual hardiness zone. Black plastic will cook the plant on sunny days and encourage fungus but not protect the plant from freezing temps. Remember this plant can't take any frost. Your best bet is to borrow a dolly and haul it indoors. Here is an article that explains over-wintering mandevilla indoors: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/winterizing-mandevillas.htm