Florence, I know nothing about gardenias. But a long time ago, I came across a gardenia post on gardenweb that has always remained in my memory. Someone has saved it for posterity. If you have time, take a look.
Kathy

Here is a link that might be useful: Infamous suicidal gardenia thread

Gosh, two have died on me, and both were outside. (The suicidal gardenia thread hits home.) I know they need acid soil and sunshine.

I'll put a link to the Fragrant Plants forum, where they often discuss gardenias. Best of luck!

Here is a link that might be useful: Fragrant Plants Forum