If your gardenia plants change from aesthetically pleasing home garden favorites to a sudden concern or eyesore, your plants are likely experiencing an underlying health problem or a need for improved care. Prized for their dark evergreen foliage and white, waxy blossoms, gardenias add a strong, pleasing aroma to the home garden. Typically blooming from May through July, blossoms can grow to a diameter of up to 4 inches. Pay close attention to any changes in your gardenias so you can catch a problem before it becomes severe.
Maintain consistent care of your gardenia plants as a preventive measure as vigorous plants have a greater capacity for avoiding or recovering from disease and pest problems than stressed or weakened plants.
Grow gardenias in areas that provide light to moderate shade for best development.
Cultivate gardenia plants in moist, well-drained soil high in organic content. Maintain an acid pH level, according to the Clemson University Extension. Test soil with a soil kit from a garden supply store and, if pH is incorrect, contact a county extension agent for a more specific soil test and directions for accurately amending your soil.
Irrigate your gardenias regularly to maintain moist soil, preferably through drip irrigation that keeps fungi-attracting moisture off foliage. Add a layer of mulch like pine needles to the area surrounding your gardenias without pressing the mulch against stems. Mulch improves water retention and keeps weeds at bay.
Deadhead flowers once they lose their vibrancy after flowering and prune any dying, weak branches.
Examine your plants for colonies of insects or apparent insect damage. Look for common pest problems like melon aphids or spider mites. Look for gardenia growth that appears malformed or curled as a symptom of melon aphids that feed on gardenia tissue fluid, displaying tiny brown or green bodies. Identify spider mites by the tiny yellowed dots they create through feeding on leaf surfaces.
Release natural enemies purchased from a garden supply store to control aphids. Select ladybugs or lacewings or apply an insecticide with the active ingredient permethrin for severe infestations. Manage spider mites with the release of the natural enemy western predatory mite or apply an insecticide with the active ingredient carbaryl.
Look for signs of common diseases that can wreak havoc on your gardenia plant. Search for fungal infections that can result in leaf drop, yellowing or wilting often caused by root rots or powderlike fungal growth or dark fruiting bodies on plant surfaces commonly attributed to powdery mildew disease.
Contact your county extension agent or a licensed professional for assistance with disease problems unless you can accurately identify the issue. Avoid attempting to treat myriad symptoms without figuring out the actual problem. For control of root rots, maintain excellent drainage and remove and destroy the gardenia if plant death occurs. For powdery mildew, remove and destroy affected plant parts and debris and apply a fungicide with the active ingredient myclobutanil, according to the Clemson University Extension.