DEAR AMOR: I’ve always loved gardenias and always wanted my own plant. This year I finally bought one in a container. It was doing well and had a few blooms but about three weeks ago the leaves started turning brown. Can you tell me why this might be happening? — Brenda
DEAR BRENDA: Gardenia is named after Alexander Garden (1730-1791), a Scottish-born American physician, botanist, and zoologist. Coveted for their milky-white and very fragrant blossoms, this gorgeous white beauty is also known as jasmine or cape jasmine.
There are more than 200 species of gardenias but none of them will survive in hardiness zone 5 and below. Their flowers are varying as well. Some double-flowered blossom cultivars may look like an open white rose. Single-flowered blossoms resemble a flower of a jasmine vine, of which I am very, very familiar.
As a potted houseplant, it need tons of tender loving care, but so does any other houseplants like geraniums and poinsettias. Gardenias are also vulnerable to diseases that attack their foliage and root structure. Nowadays, there are hardier gardenia varieties available that can be resistant to some diseases.
Sudden Browning of Leaves
Finding the root cause why the leaves of a gardenia prematurely turns brown may be answered by one of the following questions:
Was it placed outdoors on a location that received direct heat from the sun? Gardenias love bright light but not direct sunlight. A shaded area is best when placed outdoors for the summer.
Was it watered regularly? The soil of a gardenia should be moist and not allowed to dry out. However, its roots should not be sitting in water either. A soaking plant will not grow new, water absorbing roots without oxygen, resulting in dehydration instead. And yes, browning of leaves follows.
Was it given too much fertilizer? The wrong kind of fertilizer or over-application of fertilizer scorches the leaves of plants. Why? Its fertilizer-damaged roots were unable to hydrate the plant, causing its leaves to dry out and turn brown.
Was it infested by powdery mildew? Powdery mildew infection in gardenias begins as a small yellow-brown spot. As it spreads throughout, they become dark-brown leaves. Indoor plants should be spaced from one another for air circulation. Low humidity among the plants will inhibit the growth of fungal spores from germinating and infecting other foliage. Fungicides may be used to control powdery mildew.
Yellowing, Wilting, and Leaf and Bud Drop
Bug infestation, stem canker, and root rot in gardenia causes yellowing, wilting, and leaf and bud drop. A severe infection will ultimately kill the plant. If the plant has been outside, it is a good practice to repot them and check its root system before taking the plant indoors. Prune out diseased leaves, branches, or brown rotting roots.
Remember to disinfect pruning shears before and after pruning, and from plant to plant, to avoid cross contamination of mold, mildew, stem canker, or bug infestation. The use of a commercial potting soil is a good prevention from bugs and diseases later on.
Gardenia is an acid-loving plant. Iron deficiency will also cause their leaves to turn yellow. An ideal pH is 5.0-6.0. A slow-release fertilizer that is intended for acid-loving plants is highly recommended to maintain a good pH level for this sweet-scented white beauty.
Blackened Powdery Leaves
Black sooty mold is not killing the plant but is a good hint that there may be whiteflies, mealybugs, scales, aphids, or spider mites in the plant. Control is directed toward these nutrient-sucking insects that left traces of sugary “honeydew” on leaves in which this mold is feeding upon. Hand removal or insecticides maybe used.