The Mandevilla vine, a tropical and subtropical plant prized for its trumpet-shaped blooms, is typically grown as a container annual in colder climates. Successfully overwintering this plant requires a shift in care, and pruning is a necessary first step. Reducing the plant’s size before the cold season allows it to conserve energy and makes it manageable for indoor storage. These steps will ensure your Mandevilla transitions smoothly into its dormant period, setting the stage for vigorous growth next spring.
Determining the Right Time for Pruning
The timing of the initial pruning is dependent on external temperatures, as the Mandevilla is highly sensitive to cold. Begin the process before the first hard frost threatens, which can cause significant damage to the foliage and stems. Monitoring nighttime temperatures is the most reliable cue to start preparation.
It is recommended to bring the plant indoors when evening temperatures consistently drop below 50°F (10°C). Waiting until temperatures fall below 40°F (4°C) dramatically increases the risk of damage, as the plant can be injured even without a visible frost. Pruning too early, however, sacrifices the plant’s late-season growth and potential blooming.
The optimal window is typically in early to mid-fall, just as the plant’s growth naturally begins to slow down. Acting at this time ensures the vine is protected from cold stress while utilizing the last of the season’s warmth for recovery before dormancy.
Essential Pruning Techniques
Pruning for overwintering is more aggressive than routine maintenance pruning and requires sharp, sterilized tools to prevent the introduction of pathogens. Using shears cleaned with rubbing alcohol or a bleach solution minimizes the risk of transferring plant diseases. Mandevilla sap is milky and can be an irritant, so wearing gloves during the pruning process is advisable.
For dormant storage, the goal is to significantly reduce the plant’s overall size to about one-third to two-thirds of its current length. If you plan to store the plant in a cool, dark location for true dormancy, cut the vines back hard, reducing the entire plant down to a height of 10 to 12 inches. This aggressive cut focuses the plant’s energy reserves into the root system.
Any stems that are dead, damaged, or show signs of disease should be completely removed down to the main stem or soil line. When making cuts on healthy, living stems, always cut just above a leaf node. This is the slightly swollen point where a leaf or new shoot emerges, and cutting above this node encourages new growth when the plant wakes up in the spring.
Preparing the Plant for Dormancy
Once the Mandevilla has been pruned, the next steps focus on pest management and inducing a stable dormant state. Before moving the plant indoors, a thorough inspection and cleaning are necessary to prevent pests from infesting other indoor plants. Spider mites, mealybugs, and scale insects are common hitchhikers that hide on the undersides of leaves and along the stems.
Pest Management
Wash the entire plant, including the stems and the soil surface, with a strong spray of water to dislodge any visible insects. If an infestation is detected, treat the plant with horticultural oil or insecticidal soap, such as neem oil, before bringing it inside. Drenching the soil with water can also encourage soil-dwelling pests like sowbugs to vacate the container.
Storage Environment
The storage environment is paramount to successful dormancy. An ideal location is a cool, dark, or low-light area, such as a cool basement, cellar, or heated garage. The temperature in this storage area should be consistently cool but remain above freezing, typically between 50°F and 60°F (10°C to 15°C).
Winter Watering and Feeding
To encourage and maintain dormancy, water reduction is critical, as the plant’s metabolic rate slows significantly in cool, low-light conditions. Provide water sparingly throughout the winter, giving just enough moisture to prevent the potting mix from completely drying out. The soil should feel dry to the touch before you water again, and you must avoid overwatering to prevent root rot in the cool environment. Fertilizer should not be applied at all during this dormant period, as the plant is not actively growing.