Care for a dipladenia during the winter by mulching it, watering it lightly and pruning away dead stems before the growing season. For climates that have a minimum temperature below 45 degrees Fahrenheit or that are in a USDA zone 7 and below, bring the plants inside during the winter as the cold can kill the roots.
During the winter, spread 3 inches of bark or straw mulch around the plants to protect the roots from frosts in areas where the minimum temperatures hover between 10 and 20 degrees Fahrenheit or in USDA zone 8. If you live in USDA zones 9 through 11 with minimum temperatures between 20 and 50 degrees Fahrenheit, forgo the mulch.
Discontinue fertilization during the winter, and water the plant only when the soil dries out. In the late winter, snip off any dead or damaged limbs, and thin out the branches to allow for better airflow.
If you must bring dipladenias indoors during the winter, keep them in pots for easy removal. First, rinse the plant with water to rid it of any insect passengers. Place it in an area with a temperature above 45 degrees Fahrenheit with plenty of sunlight, such as a south- or east-facing window.