Bougainvillea is a vigorous, woody vine genetically programmed to scramble and spread. To train it into a tree form, you must work with, not against, its natural inclination for rapid growth. The plant's energy is directed into a few selected leaders rather than many lateral branches. This process capitalizes on its strong apical dominance—the tendency for the main, central stem to grow more strongly than its side stems. By consistently removing lower growth and suckers, you force the plant to channel its resources upward, creating a sturdy trunk and a canopy above.
Begin with a young, healthy, and vigorous bougainvillea plant with a strong, central stem that will become the future trunk. This stem should be as straight and upright as possible. Immediately insert a sturdy, durable stake (e.g., bamboo, metal rebar) deep into the soil next to the main stem. Gently but securely tie the stem to the stake at several points using soft, flexible plant ties. Do not tie too tightly, as the trunk needs room to expand in girth. This support is critical for the first few years to prevent the developing "tree" from snapping in the wind while the trunk lignifies (becomes woody) and strengthens.
The initial formative pruning is the most important step. Your goal is to establish a single trunk and a raised canopy. Identify your chosen central leader. As the plant grows, meticulously remove all side shoots and suckers that emerge from the base of the plant and along the lower portion of the designated trunk. Continue this process, allowing the central leader to grow taller until it reaches your desired trunk height. Once the leader reaches this height, pinch or cut off its tip. This action halts its vertical growth and stimulates the development of lateral branches at the top, which will form the canopy.
After the basic tree form is established, maintenance pruning is required to encourage a dense, flowering canopy and manage the plant's energy. Bougainvillea blooms on new growth. Prune the canopy immediately after a flush of blooms has faded. Use sharp, clean bypass pruners to tip-prune the branches, cutting back by a few inches. This encourages branching, which results in a fuller canopy and more flowering sites for the next cycle. Regularly remove any water sprouts (vigorous vertical shoots) that emerge from the trunk or main branches, as they divert energy from the canopy. Also, consistently check for and remove any suckers from the base of the plant to maintain the clean tree form.
The optimal time for major structural pruning is in late winter or early spring, just before the burst of new seasonal growth begins. This timing allows the plant to quickly heal wounds and direct its full energy into producing the desired new growth. Light maintenance pruning and deadheading can be performed throughout the growing season. Always ensure your tools are sterilized to prevent the spread of disease. After significant pruning, a light application of a balanced, slow-release fertilizer can support recovery and new growth. Remember that bougainvillea thrives on neglect when it comes to water and rich soil; over-care can reduce blooming.
