The Mandevilla vine is a stunning tropical perennial native to Central and South America, known for its vibrant, trumpet-shaped flowers. The plant is botanically classified within the genus Mandevilla, though the name Dipladenia is frequently used for more compact varieties. Regardless of the specific type, this plant is a tender perennial that thrives in warm climates and cannot withstand sustained freezing temperatures. For gardeners outside of its native range, understanding how to protect this plant from the cold is necessary for its long-term survival.
Defining Mandevilla’s Cold Sensitivity
The Mandevilla vine is classified as perennial only in United States Department of Agriculture (USDA) Hardiness Zones 9 through 11, regions where the average minimum winter temperature remains well above freezing. Due to its tropical origin, the plant is highly sensitive to cold conditions and requires temperatures consistently above the mid-50s Fahrenheit to flourish. Temperatures lower than 50°F are likely to cause damage, often manifesting as leaf drop.
The threshold for serious harm is 32°F (0°C), the freezing point of water, where the risk of tissue damage becomes significant. Sustained temperatures below freezing are typically lethal, as water inside the plant’s cells freezes and ruptures the cell walls. In colder zones, Mandevilla must be treated as an annual or brought indoors to survive the winter. The plant should be moved inside as soon as nighttime temperatures begin to dip into the 40–50°F range.
Short-Term Protection from Sudden Frost
When an unexpected dip in temperature threatens an overnight frost, immediate, temporary measures can protect the plant from acute injury. Container-grown Mandevillas should be moved to a protected location, such as under a patio overhang, against a warm south-facing wall, or inside a cool garage or shed. This brief shelter is often enough to protect the plant from a short-lived temperature drop just below freezing.
For in-ground or large container plants, covering the foliage provides a necessary thermal layer. Use materials like old blankets, burlap, or commercial frost cloth draped over the plant, extending down to the soil level to trap geothermal heat radiating from the ground. Ensure the covering material does not directly touch the leaves, as moisture on the foliage can freeze and transfer cold directly to the plant tissue. The covers must be removed promptly the following morning after temperatures rise above freezing to prevent overheating in the sun.
Overwintering for Long-Term Survival
For gardeners outside of tropical zones, successful long-term survival requires moving the Mandevilla indoors for the entire cold season through a process called overwintering. Before bringing the plant inside, inspect it thoroughly for pests like aphids and mealybugs to avoid introducing them indoors. Prune the long, twining vines back by about one-half to two-thirds of their length to make the plant more manageable for storage.
Two main strategies exist for overwintering: maintaining active growth or forcing dormancy. If you choose to keep the plant active, it requires a bright, sunny window that provides at least six hours of indirect light daily. Temperatures should be maintained between 60°F and 70°F. The soil should be kept evenly moist, but not saturated, and humidity can be increased with a nearby humidifier or misting.
The dormancy method is often simpler, requiring a cool, dark location like a basement or unheated garage. Temperatures must remain consistently between 50°F and 60°F, well above freezing. In this resting phase, the plant will likely drop most of its leaves. During dormancy, watering must be drastically reduced, providing only enough moisture to keep the soil from completely drying out, perhaps once a month. Fertilizing should be completely suspended in both overwintering scenarios.
In late spring, once the threat of frost has passed and outdoor temperatures consistently stay above 50°F, the Mandevilla can be prepared for its return outside. This transition requires a process called “hardening off,” where the plant is gradually acclimated to outdoor conditions. Start by placing the plant in a shaded, protected outdoor spot for a few hours each day and progressively increase its exposure to direct sunlight over a period of one to two weeks. This slow reintroduction prevents the leaves from being scorched by the intense summer sun.
Recovery from Frost Damage
If a Mandevilla has been subjected to freezing temperatures, assess the damage by looking for visual cues like blackened, limp foliage and soft, water-soaked stems. While the appearance may be discouraging, do not immediately prune away the damaged material. The dead leaves and stems serve as a layer of insulation, offering slight protection to the underlying plant tissue against further cold weather.
Wait until the last danger of frost has passed in early spring before performing corrective pruning. Use sharp, clean shears to cut the stems back to healthy, firm wood, which is indicated by green tissue just beneath the bark. If the stems are completely brown and appear dead all the way to the soil line, cut the entire growth back to a few inches above the ground. The root system may still be alive and capable of sending up new shoots.