Are you in an area that gets year round rainfall, or seasonal? Plants such as Pyrostegia do best if they get a dry period, and in habitat would have a dry winter season when it would also be cooler, such as they get in Hong Kong. The Adenium might also be affected by too much rainfall. Adenium might do better if grown as a container plant, in a fast draining soil mix. This seems to work well for them to bloom over a long season in places like Malaysia and Singapore, which are both hot and rainy all year round.

I had always thought that the Thunbergia mysorensis would do better with year round heat and rainfall, but only know it personally as it is grown here in California, where it only blooms in the warmest months, but seems to bloom nearly all year round when grown as a greenhouse plant with temps above 65F.

There is a dry season between from Dec-March but again temperture rarely goes below 70. I was mistaken when I said Tibouchina Grandifolia bloom here they actually die from the heat I am guessing. Thunbergia Grandifolia blooms all year but nothing from Thunbergia Mysorensis. So it is either the warm night time tempartures or something lacking in the soil?