I just got a gardenia bonsai, March 20 of this year, like to keep it indoor since it has been moved and i believe it is stressed, it has been dropping leaves, but it is getting buds, which makes me very happy, don't know if I should fertilize it or just leave it where it is next to a south window. Thank you for any advice, I am a beginner.

One of the most common advices here is do not fertilize an unhealthy or stressed tree. Since the tree has been moved recently, is indoors, is a quite fussy species and that you are a beginner I would say no.

Mowe the tree outside as soon as temperature is safe above 15c. If you see a good growth after that you can start give fertilizer.