Certified GKH Gardening Expert
First, make sure your jacaranda tree is growing in an appropriate environment for the species. Jacarandas need well-drained, preferably sandy soil, and they flower best if their soil is not very rich in organic matter.
Check this article to see if your jacaranda may have one of the problems discussed here:
Also, exposure to excessive nitrogen fertilizer or lack of phosphorus in the soil can cause many plants to flower poorly.