Gardenias need to be sprayed with a fungicide that is gardenia safe. Check on the bottle to make sure it is safe for gardenias. It probably has a fungus which is common in gardenias as long as you see no bugs on it. Get a good fungicide and spray the plant and it should do fine.
I Have A Potted Gardenia On My Windowsill. It Has A Sticky Substance On The Leaves And A White Powdery Substance On The Stems. The Buds Turn Brown And Drop Off And The Leaves Turn Yellow And Then Brown. What Can I Do?
It is caused by white-flies or a fungus, put it outside to get just morning sun and it should disappear in a short while...meanwhile spray with an anti-fungal and it is getting way too much moisture.