Good points, Longy.
Also, SSharpless, gardenias like humidity. Place a pebble filled saucer under the pot and keep an inch ot two of water in it. The plants love being misted too.
turn from cream to yellow as the open flower
ages. If it's new flowers
that are yellowing, I'd say too much food, as Longy says.
No, it won't live outdoors over winter in your area. It's a tropical, and must be warm and kept misted or saucer-ed indoors. Indoor heat and dry air can kill it too, which is why you want to do the saucer.
If you have any pets, make sure they don't drink the water from the saucer-the water will have plant food in it.