Anna - gardenias are funny they can be a little finicky at times. I can't say, even with all of the gardenias that I've had, that I am experienced with that particular cultivar… But I know that mine range from doing best in full sun to others to do better in part shade. Make sure that that soil is not staying wet I don't know if you amend your potting soil or not but using some thing like chicken grit and/or coir is good. I also don't do well with potted gardenias all of mine are in the ground. That being said I can't speak to measurements but Gardenias benefit from Epson salt, fish emulsion, and even a little Holly Tone - you just want to be careful with it being in a pot when using those items. i've also seen gardenias drop all of their leaves for whatever the reason and when given good care of bounce back. Unless there is no green bark when scratched at the base I will continue to try to revive them.
