Bougainvilleas may not bloom if they are overwatered, are exposed to light at night, are not pruned, have not been properly fertilized or do not have enough sun. There are also some types of bougainvilleas that do not bloom until the fall.
If bougainvilleas are overwatered, they may not bloom as the plant has no incentive to seed rapidly. In some plant nurseries, gardeners withhold water from bougainvilleas for up to three months. After this time, the plants are watered heavily. This causes the bougainvilleas to flower as the plants are tricked into seeding and propagating quickly.
Pruning back a bougainvillea can also induce flowering. Long, trailing stems must be pruned back 20 to 30 inches in some cases in order to encourage new flowers.
Proper fertilization practices can also help in forcing the plant to flower. Hibiscus fertilizer, along with Epsom salt, can be added to the soil every three to four weeks during spring and summer. Nitrogen-rich fertilizers are not recommended.
Bougainvilleas also need to have their roots crowded somewhat in order to help the plant bloom. Growing the bougainvillea in a pot for growing season and then transplanting it helps in bringing the plant to bloom. Growing pots for bougainvilla must have good drainage.