Bougainvillea is a vibrant, woody tropical plant cultivated for its brilliant, papery bracts. Although often treated as a vine, it lacks the biological mechanisms of true climbing plants. Using a trellis is not necessary for the plant’s survival, but rather a choice dependent on the desired vertical shape and garden application. If the goal is to cover a wall or pergola, manual support is required.
The Scrambling Growth Habit
Bougainvillea is fundamentally a woody shrub with a vigorous, sprawling growth habit, distinguishing it from true clinging vines. It lacks specialized structures like adhesive rootlets or tendrils that allow it to naturally attach to flat surfaces. The plant grows outward and upward, producing long, arching canes that seek support from nearby objects.
The plant’s primary means of vertical anchorage are its sharp, curved thorns, which are modifications of the stem tissue. These thorns function like small hooks, catching onto other plants or rough surfaces like fences. This mechanism allows the bougainvillea to scramble and lean, but it does not provide the secure, self-clinging attachment needed for vertical training. Because its growth is powerful and rapid, any vertical framework must be robust enough to bear significant weight.
Manual Support and Trellising Techniques
Achieving vertical coverage on a trellis, arbor, or fence requires direct intervention from the gardener. Since the stems do not automatically twine or adhere, they must be physically guided and secured to the support structure. This process is often called espaliering, where branches are trained to grow flat against a vertical plane.
To prevent damage to the rapidly thickening stems, soft materials like cloth strips, flexible plastic ties, or garden twine should be used for attachment. These ties must be looped loosely around the stem and the support, ensuring they do not constrict the cane as it expands. Regular inspection is necessary to loosen or replace ties before they girdle the wood.
Initial training involves selecting the strongest canes and tying them directly to the structure at regular intervals, directing growth horizontally or vertically. Any support system, whether a metal arbor or a wooden trellis, must be strong enough to withstand the weight of a mature bougainvillea. Positioning the support slightly away from a wall allows for better air circulation and provides space for the stems to be tied without damaging the wall surface.
Training Bougainvillea Without Support
The bougainvillea’s natural tendency to sprawl can be redirected through focused, heavy pruning, allowing it to be cultivated without vertical support. By consistently cutting back the long, rambling canes, the plant develops a dense, self-supporting woody structure. This technique creates a rounded, free-standing shrub or hedge.
For a tree-like standard form, a single, straight stem is selected, staked for initial support, and cleared of all lower side shoots. The canopy is formed by pinching and pruning the upper growth to encourage dense, compact branching. This structural pruning is most effective when performed in late winter or early spring, just before the primary growing season, to maximize new, shapeable growth.
Pruning cuts should be made just above a leaf node, which stimulates new lateral growth and increases the bushiness of the plant. In containers, this rigorous shaping is necessary to maintain a manageable size, resulting in a more compact, floriferous specimen. The ability to shape the plant into ground cover, a container specimen, or a dense shrub confirms that a trellis is a choice of form, not a requirement for cultivation.