Tips on how to preserve Mandevilla through the winter months.
Mandevilla (Dipladena) are tropical vines, hardy (depending on cultivars) in zones 9-11. They tolerate a minimum temperature of 45-50 F at which time growth will begin to slow down. In colder regions it is usually grown as an annual but can be saved indoors for the next season. For winter storage keep the plant outside as long as possible before bringing it indoors. Check the plants for insects and spray with insecticidal soap if needed.
Two ways to winter over Mandevilla
Treat it as a houseplant. Mandevilla can be trimmed to make it more manageable indoors and it needs a bright, sunny window to flourish through the winter. You will get some yellowing and leaf drop due to lower light and humidity. Water once a week, keeping it on the dry side. Don’t fertilize in the winter. In spring, when you see new growth, increase watering and start to fertilize.
2. Dormant stage
Another way to winterize mandevilla is in a dormant stage by storing it in a garage or cool basement with temperatures around 45-55F. Cut it back to about 12 inches above the soil line and treat for insects if needed. Keep it dry but not completely dry. Check periodically for soil moisture. Mandevilla will eventually drop all its leaves. The important thing is that you want to keep it alive through the winter.
In early spring, prune back any spindly winter growth and if pot bound repot in fresh soil. When new shoots begin to grow, fertilize lightly and move the plant to a sunny window. Pinch the new growth to get a bushier plant. Set it outside when danger of frost has passed or night temperatures are above 55.