I have mine in full florida sun in a pot on the patio. My neighbor has hers in the ground, no supplemental water except rain water (which we tend to get at least a couple times of week in the summer). So based on that...I would say high humidity, high light and ample water when dry. I've just got a baby one, but I also have a flowering michelia alba...and if the champaka is like the alba, I can't wait! Good luck!

I live in California, have mine in part sun, and when it's over 100, I water mine every day, because we have no humidity to keep stuff damp. If you are going to ask about watering needs, you are going to need to state the conditions in which you live.