Why is my bougainvillea not flowering?

Bougainvillea blooms best under stress. If yours has lush green growth but no colour: you are watering too much and feeding too much nitrogen. Withhold water for 2–3 weeks until slight wilting, then resume — this stress triggers flowering. Feed with phosphorus-potassium fertiliser, not nitrogen. Bougainvillea also needs to be slightly root-bound; a large pot reduces flowering. Full sun (8+ hours) is non-negotiable. Prune after each flowering flush.