Answer: I think the nursery professional is on the right track. The most common reasons for non-flowering are 1)immaturity, 2) lack of sufficient sunshine, 3) too much nitrogen fertilizer. At 4 years of age, your champaca is certainly old enough to produce flowers so we'll eliminate immaturity as a cause. Morning sun but afternoon shade may not be quite enough direct sunshine for your tree, especially in your mild year around climate. 6-8 hours of sunshine would be better. Since your plant is in a container, why not move it to another garden spot where it will get more direct sunshine? Leave it there until next spring. I'll bet your tree flowers for you after a few months of more sunshine. As for fertilizing, if you use a fertilizer high in nitrogen, you'll end up with lots of lush, green growth, at the expense of flowers. So, a 0-10-10 fertilizer would not supply nitrogen, but would supply phosphorous (to encourage bloom), and potassium, for strong root and stem growth.
You have nothing to lose and everything to gain (in terms of flowering) if you move your champaca. Give it a try - I bet your tree will reward you with its fragrant flowers.
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