Pruning is essential for japanese tree lilac, because it promotes blooming, ensures air circulation, and prevents problems such as powdery mildew. Prune the plant every year to keep it in its shrub form. If it is not pruned, it will grow to 4.5 to 6 m, and the blooms will gather at the plant top. Because very young and old branches do not bloom well, regular pruning is required to keep it blooming beautifully every year.
Generally, branches with a diameter of 5 cm or more should be pruned off. Prune less than 1/3 of all branches and keep 8-12 branches of different ages with a diameter of 2.5 to 5 cm. Finally, maintain the plant at 2.5 m tall or less.
Old, dead, and diseased branches, and most seedlings growing from the roots, can be cut from the base after blooming at the end of winter or late spring. The old branches are usually coarse, with weak blooming ability. Dead and diseased branches will not grow new buds or flowers in spring. Keep 2-3 strong seedlings as new branches. Any branches that disturb the tree shape or are twisted can be pruned at the same time.
If you do not need to harvest the seeds of the japanese tree lilac, cut blooms off when they begin to fade and droop. This prevents nutrient use for fruit development, and next year's flower buds will be stronger. When the center of the tree is overcrowded, choose the thickest stem and cut it off at the base to improve sunlight and ventilation inside the shrub.
If your japanese tree lilac is old, overgrown, or blooming poorly, the whole plant can be pruned to 15 to 20 cm tall. It will not bloom for three years, but the number of flowers will increase significantly.