Want to keep the mandivellas flowers for next year

Mandeville Don t do well inside without a serious amount of light. And heat. You can overwinter them by investing on grow lights that also produce heat. Place the lights a couple feet above the plant, and leave on about the length of a summer day. 7 am to 8 pm. Time the lights with any plug in timer. Use warm water when the soil feels as if it's dried a bit, but before it's DRY. Feed with a good houseplant fertilizer. I like to fertilize every couple weeks.

I found an article that goes into wintering your Mandeville with another option. It will be easier if you read it yourself to glean which parts you consider important. It does say to bring it in before temps reach sixty degrees. Here is the site: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/winterizing-mandevillas.htm

I hope this helps you!