The Dipladenia is a popular tropical flowering plant, often grown as an annual or houseplant, recognized for its showy, trumpet-shaped blooms and glossy foliage. The question of whether it is a vine is a common point of confusion among gardeners. While its flexible stems allow it to be used in ways a vine might be, the plant is botanically classified as a scrambling shrub or sub-shrub. This distinction is important because Dipladenia lacks the specialized structures, like tendrils or aerial roots, that allow true vines to climb without human intervention.
Understanding Dipladenia Growth Habit
The natural growth pattern of Dipladenia is characterized by a mounding or trailing habit, making it an excellent choice for hanging baskets and containers. Its stems are woody near the base, providing a sturdy foundation, but the new growth at the tips remains soft and highly flexible. This flexibility allows the plant to sprawl outward and cascade over container edges, creating a full and rounded appearance.
Dipladenia is not a true vine because of its inability to self-climb by twining or adhering to a support structure. True vines use mechanisms like grasping tendrils or adhesive discs to secure themselves as they grow vertically. The stems of the Dipladenia will lengthen and reach, but they will simply flop over unless they are manually secured to a trellis or stake. This natural tendency to bush out or trail defines its classification as a scrambling shrub.
Distinguishing Dipladenia and Mandevilla
The confusion surrounding Dipladenia stems from its close botanical relationship with Mandevilla; both are part of the Apocynaceae family. Historically, Dipladenia referred to compact, shrub-like species, while Mandevilla was used for the larger, vigorous vining types. Today, most commercial Dipladenia cultivars are selectively bred to maintain this compact, mounding, and bushy habit. Mandevilla types, by contrast, possess aggressive, twining stems that rapidly wrap around any available support, sometimes reaching heights of 10 to 20 feet in a season.
The leaves on Dipladenia are smaller, more pointed, and have a high-gloss finish. Vining Mandevilla usually has larger, broader, and less glossy foliage. Modern hybridization has blurred these lines, creating varieties that combine the compact nature of Dipladenia with the larger flowers of Mandevilla, but the general growth habit distinction remains valid.
Training and Pruning for Desired Shape
Achieving a vertical display with Dipladenia requires training. To encourage upward growth, the flexible stems must be loosely tied to a vertical support, such as a small trellis or wire hoop, using soft garden ties. As the plant grows, new stems need to be guided and secured regularly to maintain the desired height and shape. Pinching back the soft, growing tips of the stems encourages the plant to branch out laterally, creating a much thicker and more flower-laden appearance.
Pruning is an important tool for managing the Dipladenia’s shape, whether the goal is a vertical accent or a dense, bushy container plant. For aggressive shaping or size control, especially before bringing the plant indoors for winter, stems can be cut back by as much as one-third to one-half their length. The best time for this heavier pruning is in the late winter or early spring, just before the start of the new growing season. Always make cuts just above a leaf node or a branch junction, as this is where new growth will emerge.