I moved this to the Bonsai Forum, where I think you'll get a faster response. My first recommendation would be to use the Search Box at the top left of your page to get information on a specific type of plant; this is the site search page for [url=https://www.helpfulgardener.com/forum/gsearch_result.php?cx=partner-pub-5070231769909047%3Aflz8arcctdh&cof=FORID%3A10&ie=ISO-8859-1&q=gardenias&sa=Search#1285]gardenias[/url] It's an easy way to find stuff you need. If nothing there has answered your question usually somebody turns up with what you need to know...
Here's a [url=https://www.uri.edu/ce/factsheets/sheets/gardenia.html]fact sheet[/url] that I like. My experience with that plant was years ago, before I converted to organics, I should probably try it again. But it was all so unsuccessful I do not feel qualified to speak cogently on the topic. Sorry.