I "inherited" a couple large Gardenia
plants and have success keeping them alive and well. What I was told is to mist them, keep them pretty consistently moist and give about one cup of epsom salts to a gallon of water about once a month. Mine have turned brown as you say and when I think "Uh~oh" they start to get new growth and look good all over again! I am in PA and have one in my downstairs family room were it is a little cool and one upstairs in my living room where it is warm and that one does better but both look good and have just recently bloomed. I haven't seen brown for awhile, maybe fall. WHen mine get brown I take them outside if possible and shake all of that off.
Hope that helps you, I come from a
greenhouse family where my husbands Grandma has raised these and several other
plants for most of her life. She told me how to care for them so hopefully that answers some of your questions!
Good luck!
but I'm sure there are people here who will be able to answer it. Glad to have you aboard. 
