Answer: There are many things that cause chlorosis (leaf yellowing) and leaf drop. One cause is a common plague to gardenia - they are very susceptible to spider mites, which cause tiny webs on the undersides of leaves and where the leaves join the stems. Another way to detect them is to take a sheet of white paper out to the bush, tap a few branches on to the paper, fold the paper in half and press/rub together. If you see little red, blue, or brown smears, those are spider mites. If you do have spider mites, they will soon spread to the other gardenias. A product called Neem can be used to treat for spidermites. You can purchase it from Gardens Alive, 5100 Schenely Pl., Lawrencburg, IN 47025; ph# 12/537-8650). <br><br>Gardenias need at least a half day of full sun to bloom. Buds that turn black or drop and bottom leaves that are yellowed are sure signs that gardenias aren't getting enough light. Leaf drop can also be caused by improper soil pH (gardenia require 5-5.5pH - on the acid side.) Although if all these gardenia are growing side by side, I can't imagine the soil is bad in that one spot. Perhaps have a soil test performed just to be on the safe side. That can also eliminate other problems...yellowing and leaf drop are also signs of various soil nutrient deficiencies such as nitrogen, zinc, and iron. Or, you could have excess sulfur. Are the gardenia near a roadway? Too much sulfur can be a result of air pollution from combustion. Soil test results would give you all of these answers,and help you with solutions. Speak to your local County Extension Agent (ph# 713-855-5600) for details. While you are waiting, provide the gardenia a good helping of organic material such as compost or composted cow manure - it's like chicken soup for plants.
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