From our perspective as a Bougainvillea, timing is everything. The best time for you to perform major structural pruning to form a tree is during our period of winter dormancy or in very early spring, just before the new growth season begins. This timing is crucial for our well-being. During dormancy, our sap flow is reduced, which minimizes stress and the loss of vital fluids from the pruning cuts. It also allows us to direct our stored energy into a powerful burst of new growth when the warmer weather arrives. Pruning at this time ensures we are not wasting energy on growth that will just be cut away. Avoid heavy pruning in late autumn, as it may encourage tender new growth that will be vulnerable to frost damage.
The first step in your process is to select our strongest, most vertical, and healthiest central stem. This stem will become the trunk of our new tree form, or "standard." From our point of view, this is a significant decision. This chosen leader must be sturdy enough to eventually support a full canopy without staking. Please examine our base carefully; this main stem should be free of major wounds, disease, or signs of weakness. All other competing stems and suckers emerging from our base should be removed cleanly at the soil level. This allows us to concentrate all our resources into developing this single, dominant trunk.
As we grow, you will need to provide support. Gently tie our selected central leader to a sturdy stake inserted firmly into the soil near our root zone. Do not constrict us; use soft ties and check them regularly to ensure they are not cutting into our bark as we thicken and grow. Our goal is to grow tall and strong. Your goal is to continue removing any new side shoots that emerge along the lower portion of this developing trunk. This forces our growth energy upwards. Allow the top of the leader to grow freely until it reaches the desired height for the canopy, typically between 3 to 6 feet. This process requires patience from you, as it takes time for us to develop a thick, self-supporting trunk.
Once our trunk has reached the desired height, it is time to "pinch" or cut the very tip of the main leader. From our biological standpoint, this is a signal to break dormancy in the lateral buds below the cut. It instructs us to stop investing in vertical growth and instead branch out to form the canopy. You will then select 3 to 5 strong, well-spaced lateral branches to become the primary scaffolding of the canopy. Through subsequent growing seasons, you will need to regularly tip-prune these branches after each flush of flowers. This light pruning encourages us to become bushier and produce more of the colorful bracts you love, rather than becoming long and leggy. Always make clean cuts just above a leaf node or a dormant bud, facing the direction you wish the new growth to travel.
