The Mandevilla vine (often sold as Dipladenia) is a popular tropical perennial known for its vibrant, trumpet-shaped flowers. Since it cannot survive freezing temperatures, it is typically grown as an annual in temperate climates. To preserve the plant across multiple seasons, gardeners must bring it indoors before cold weather begins. Successful overwintering requires careful transition and environmental management until spring.
Preparing the Mandevilla for Winter
The move indoors must be timed precisely to avoid cold shock. Mandevilla plants are highly sensitive and should be moved inside when nighttime temperatures consistently fall below 50°F (10°C). Moving the plant before the first hard frost is imperative, as freezing temperatures will destroy the foliage and potentially kill the root system. This minimizes stress and prevents the detrimental effects of sudden cold exposure.
Pruning is necessary to prepare the large vine for a confined indoor space. Reduce the plant’s size by cutting back the long, vining stems by one-third to one-half for manageability. This reduction concentrates the plant’s energy toward the main stem and roots, reducing the surface area requiring resources during low-light winter months. Discard the trimmed material to remove any existing pests.
A thorough pest inspection must be completed before the Mandevilla is brought inside. Tropical plants frequently harbor common pests like spider mites, whiteflies, or scale insects that can quickly spread to other houseplants. Scrutinize the entire plant, including the undersides of leaves and the soil surface.
If pests are detected, treat the plant with an insecticidal soap or horticultural oil a few days before the move, following product directions. As a final preparatory step, spray the plant thoroughly with a strong stream of water to dislodge any remaining insects. Allowing the soil to dry slightly before the move reduces the risk of introducing fungus gnats, which thrive in overly moist indoor conditions.
Indoor Care and Dormancy Management
The specific care required during winter depends entirely on the temperature of the chosen indoor environment. Mandevilla care is divided into two distinct methods: forcing a cool, dormant state or maintaining active growth in a warmer setting. The decision between these two options is determined by the temperature and light availability within the home.
Forced dormancy is the best option when a bright, warm indoor space is unavailable. This process involves placing the plant in a cool, dark location, such as a cellar or cool basement, where temperatures remain consistently between 50°F and 60°F (10°C to 15.5°C). In this cooler range, the plant naturally slows its metabolic rate and enters a resting period.
During dormancy, the Mandevilla requires minimal attention; light is not necessary, and the plant will likely shed most or all of its foliage. Water should be applied sparingly, only enough to prevent the soil from becoming completely desiccated. Overwatering during dormancy is a common mistake that leads to root rot, so allow the soil to dry out significantly between the very infrequent waterings.
Alternatively, if the Mandevilla is kept in a standard living space with temperatures consistently above 65°F (18°C), the plant will attempt to maintain active growth. This method requires significantly more resources to be successful throughout the winter. Place the plant near the brightest south-facing window possible to compensate for the lower intensity of winter light.
When keeping the plant active, supplemental lighting, such as a dedicated grow light, may be necessary to prevent the stems from becoming thin and elongated (etiolation). The plant requires more frequent watering than a dormant plant, though still less than it did during the summer. Allow the top inch or two of soil to dry before watering again to maintain a healthy balance.
Pest monitoring is mandatory throughout the winter, regardless of whether the plant is dormant or actively growing. The dry, warm air inside homes creates an ideal breeding ground for pests, particularly spider mites, which rapidly colonize stressed plants. Regular, close inspection of the leaves remains the best defense against infestation.
If pests are discovered, immediate treatment with insecticidal soap is necessary to protect the plant and surrounding indoor flora. Proactive treatment with a gentle misting of water can also help deter spider mites, as they prefer low-humidity environments. Maintain elevated humidity by placing the pot on a tray filled with pebbles and a small amount of water.
Reintroducing the Mandevilla Outdoors
The Mandevilla should not be moved permanently back outside until all danger of frost has passed for the season. Nighttime temperatures must consistently remain above 55°F (13°C) before the plant can safely transition to its summer location. Moving the plant out too early risks exposing tender new growth to a sudden and damaging cold snap.
The most important step in the spring transition is the process of hardening off, which prevents severe sun scald and shock. The plant must be gradually reintroduced to the intensity of direct sunlight and wind over a period of seven to ten days. Start by placing the Mandevilla in a deeply shaded, protected location for only a few hours each day.
Over the following days, incrementally increase the plant’s exposure time and move it to slightly brighter locations. This slow adjustment allows the plant’s leaf cells to rebuild their protective cuticle layer, which thinned out during the low-light winter months. Rushing this process will result in white or scorched leaves that cannot recover.
Once the Mandevilla is settled in its final outdoor location, normal watering practices should resume. This is the ideal time to apply a weak, balanced liquid fertilizer to encourage robust new growth and flower production. Before fertilizing, prune away any dead or spindly stems that developed indoors to shape the plant and direct energy toward healthy development.
If the plant has been in the same container for several seasons, the spring transition offers an opportunity to repot it into a slightly larger container. Alternatively, remove the top few inches of old soil and replace it with fresh potting mix, a process known as top-dressing. This action refreshes the nutrients and improves the overall soil structure as the growing season begins.