Bring your Mandeville indoors when the night temperatures are consistently in the upper 40’s. The best time to make the move is when you bring your houseplants inside, which is usually done when indoor temperatures are similar to that outdoors. Treat it with an insecticide so you do not bring in any pests.
If you have plenty of sunlight and room you can treat your Mandeville like a houseplant and keep it inside your home over winter. Place the plant in a sunny location and water as needed. Allow it to dry out slightly. It may go dormant anyway and lose its leaves, in which case you should cut back on watering severely to prevent root rot.
You can also keep a Mandeville any place where temperatures stay between 55 and 60 degrees, such as a basement, crawlspace or garage. Cut the plant back to about 12 inches above the soil and then wash the remaining leaves to remove any pests you don’t want to over winter with the plant. If your Mandeville is growing in a container you may want to flush the soil with water to eliminate ants, spiders and the like.
Once the plant is moved into storage cut back on water. You only need to water it occasionally. Just don’t let it dry out completely. And there is no need to fertilize the plant over winter at all. In the spring after all danger of frost has passed and temperatures are consistently above 60 degrees F, you can move your Mandeville back outside. Don’t be alarmed if growth produced over winter burns off. This is fairly common. Begin watering on a regular basis and feed with a liquid fertilizer and in no time you will have beautiful flowers again!