The Mandevilla, often recognized by the common name Rocktrumpet, is a popular tropical vine admired for its showy, trumpet-shaped flowers that bloom continuously throughout the warm season. This plant is a vigorous grower, and for most varieties, some form of vertical support is necessary to encourage upward growth and maximize the plant’s ornamental appeal. The extent of this need, however, depends on the specific variety, as modern breeding has introduced plants with different growth patterns.
The Mandevilla’s Growth Habit
The need for a support structure is rooted in the Mandevilla’s biological classification as a twining vine. This plant climbs by wrapping its new, flexible stems around any available vertical element, a mechanism distinct from vines that use adhesive roots or specialized tendrils. The growth is typically rapid, with some vining cultivars capable of reaching up to 10 to 20 feet in a single growing season when conditions are favorable.
If a climbing Mandevilla is left without proper staking, its long shoots will become tangled, creating a dense, messy mound that can potentially damage itself by restricting air circulation and light exposure. For example, the well-known ‘Alice du Pont’ variety is a true climber that requires substantial support to manage its height.
The true vining Mandevilla must be differentiated from its close relative, Dipladenia, which is often marketed interchangeably. Dipladenia varieties are generally more compact and shrub-like, typically staying under five feet tall. These varieties, and newer mounding Mandevilla selections, require minimal to no support, making them suitable for hanging baskets or container arrangements. When selecting a plant, look closely at the label or the plant’s current form to determine if you have a true vine or a compact shrub.
Selecting the Right Support Structure
For the vining Mandevilla, the support structure must be selected and installed with its mature size and weight in mind. The support should be placed either before or shortly after planting to prevent damage to the young, actively growing stems. A structure that is too small or flimsy will eventually be overwhelmed by the vine’s rapid growth, especially when the foliage becomes heavy with water after rain or watering.
Traditional structures like vertical trellises, obelisks, and arbors are excellent choices, offering a stable framework for the vines to ascend. The support must be vertically oriented and securely anchored into the ground or a heavy pot. For container-grown Mandevillas, simple bamboo stakes or wire cages can be inserted directly into the pot, often tied together at the top to form a teepee.
Narrow posts or columns require the use of materials like fishing line or soft twine stretched horizontally to give the twining stems sufficient purchase. Mandevilla stems prefer to wrap around structures that are relatively thin, so a broad, flat wall or fence will not work without additional, closely spaced vertical elements or netting. The structure needs to be sturdy enough to handle a vine that can easily reach heights of 10 to 15 feet within a single growing season.
Training and Pruning for Shape
Training the Mandevilla onto its support requires some manual intervention, as the young vines often need guidance to find their way up the structure. The gardener must gently weave the new, pliable shoots around the support, paying attention to the plant’s natural twining direction, which can be clockwise or counter-clockwise. If the vine is wrapped against its natural tendency, it may eventually unwind itself from the structure.
Loose ties made from soft fabric or biodegradable twine can be used to temporarily secure the stems to the trellis until they begin to twine on their own. Periodically checking the plant and adjusting any wayward stems ensures a full, aesthetically pleasing coverage of the support structure.
Training and Pinching
Pruning is an important technique used to manage the vine’s size and encourage a bushier habit, which is particularly useful for container plants. Pinching back the tips of young, vigorous stems encourages the plant to branch out laterally, creating a denser, more foliage-filled appearance.
Rejuvenation Pruning
For vines that are becoming too aggressive or leggy, cutting back the oldest stems by up to one-third of their length, ideally in late winter or early spring, helps rejuvenate the plant and promotes new, flower-producing growth. In cases where a vining Mandevilla is grown without vertical support, such as in a hanging basket, heavy and regular pruning is the primary method used to maintain a compact, trailing form.