桂花 tree is about to die?? can I save it?

like most of us all, we were growing up in city, lucky enough now have a little yard to grow something I like..

recenly I covered a bag of pot mix ( I thought it gives more nutrition) on top of soil... but it started to dry out... all the leaves are drying out...    I am keep watering ... nothing reversing.... what kind of fertilizer can take it back...

I just want those sweet smelles come back..... help!