Answer: It is really difficult to diagnose a plant problem without seeing the plant. I can offer general cultural guidelines:
Royal poinciana is very fast growing, about 5 ft (1.5 m) per year until maturity, and tolerant of a wide range of well drained soils from acidic to alkaline and from loamy to gravelly. It's best to provide protection from strong winds.
Light: Full sun.
Moisture: Royal poinciana is drought tolerant, but does best with regular water in the growing season and very little water in its dormant season.
Hardiness: USDA Zones 10 - 12. Royal poinciana should not be exposed to temperatures below about 45?F (7.2?C).
If the growing environment is not what it requires, that might be why your Roal Ponciana is ailing. Try to correct the conditions and it may recover. Hope so!
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