Why Are My Gardenia's Leaves Turning Black?

When terrible things happen to your plants, who are you going to call? The all-knowing Grumpy, of course! Who else would know why your gardenia's leaves are turning black and what you can do to fix it?

The photo above shows gardenia the way it's supposed to look. Voluptuous, seductive, waxy, white blossoms redolent of intoxicating perfume. Glossy, deep green, healthy leaves. So what's going on  in the gross picture below?

emSooty mold on gardenia. Photo: farmcarolina.com/em

A desperate Lisa Phillips writes: "My gardenia bushes are being attacked by some kind of small insect and black mold.  I have sprayed the bushes with detergent and water several times and treated with Sevin dust, but the bushes are still showing mold. HELP! I don't want to lose these bushes, as they are an old variety that produces large fragrant blooms."

Grumpy replies: Relax, Lisa. Release those endorphins. Grumpy has come to the rescue. Your gardenias are probably under siege by sucking insects, such as aphids or whiteflies. These bugs secrete a sticky honeydew as they feed. Black, sooty mold then grows on the honeydew. Get rid of the bugs and the mold will go too.

To do this, spray your gardenias according to label directions with horticultural oil, making sure to wet both the tops and undersides of the leaves, as well as the stems. You may have to spray more than once. Or apply a systemic insecticide that's absorbed by the plant and lasts a long time, such as BioAdvanced Tree & Shrub Protect & Feed. You can purchase it at garden centers.

One more problem expertly solved!