Gardenias are fragrant but finicky flowers

Q: I purchased a gardenia this spring at the nursery. How do I take care of it? - Alyssa from Walden 

A: Gardenias are prized by gardeners for their highly fragrant flowers and bright, glossy, evergreen foliage that’s attractive year-round. When given the right growing conditions, these heat-loving shrubs will perform well.

Gardenias are subtropical plants that thrive in warm, humid weather. Most gardenias are hardy in zones 8-11, though a few varieties hardy to zone 7 have been developed (Kleim’s Hardy), and a few are only hardy in zones 10 and 11. This means in our zone they must be brought inside before frost. 

While all gardenias have fragrant flowers, there are differences from variety to variety in mature size and bloom time. There is a gardenia variety to suit just about every need from compact smaller varieties that mature to 4 feet tall (such as Everblooming Gardenia) and others that can reach 8 feet tall and wide (such as First Love® Gardenia). Also, take into account blooms and bloom time. Some gardenias offer fewer but super-large (4-inch diameter) blossoms while others have smaller but more abundant flowers. By growing several gardenias with different bloom times, it’s possible to have a sequence of flowers during the season. 

In their hardiness zones, gardenias are considered a landscape shrub, not an indoor plant, despite the fact that they are often sold in the nursery trade as such. If you wish to grow gardenias in our area, they need to be taken indoors during cold periods, typically between October and May. Two limiting factors to indoor gardenia health are light and humidity. It is almost impossible, without a greenhouse or sunroom, to get the plants enough sunlight for them to set and retain flower buds. Sometimes indoor gardenias will grow flower buds, but the buds will drop before opening. Placing the plant in a south-facing window that protrudes slightly so that sunlight reaches the plants on three sides will give you the best chance of success. To elevate humidity, use a humidifier placed near the plants in the room where the plants are growing. Misting the leaves is a temporary relief. 

If you wish to try to grow them indoors, here are some of their cultural requirements. Gardenias require a soil pH of between 5.0 and 6.5, which is considered acidic to slightly acidic. In addition to the right pH, the best soil for gardenias will be a lightweight and full of organic matter with good moisture-retention properties. Constant moisture is non-negotiable for gardenias. They’re not drought-tolerant, but they also don’t want soggy roots. Gardenias grow best when they are watered deeply once a week. 

If you need to repot, gardenias, much like camellias, like to be planted a little high. Avoid cultivating around the root zone of gardenias once they are established. They do not like to be disturbed. 

Apply a slow-release fertilizer for acid-loving plants in the mid-spring and mid-summer. 

Prune gardenias to maintain size in the summer after they finish blooming and throughout the year to remove dead or diseased growth as necessary. You can prune the shrubs hard after blooming, but they may not flower as profusely the next year. 

Some problems associated with growing gardenias:

Sooty mold: Sooty mold is a dark, fuzzy mold that covers the plant leaves and is a symptom of a whitefly or aphid infestation. Rid plants of those pests using insecticidal soap.

Bud drop: Lack of adequate water during the summer can cause bud to drop so it’s important to always irrigate during dry weather. Lack of sunlight can also lead to bud drop or even cause the plants not to form flowers. Finally, insect problems from aphids or whiteflies can cause bud drop. Eliminate issues one by one, and you’ll have a gardenia covered in blooms.

Yellowing leaves: Root rot can lead to yellowing leaves. Try to pull the plant up. If it comes out easily and the roots are mushy, root rot is the culprit and the plant should be discarded. Iron deficiency causes yellow leaves; adjust the soil pH.

Failure to set flower buds: Usually when a gardenia flat out won’t produce flower buds it is growing in too much shade. Move it where it will get more sunlight. Sometimes an aggressive late summer pruning will interfere with flowering as well.

Debbie Lester is the community horticulture educator for Cornell Cooperative Extension Orange County.