Gardenias are evergreen shrubs. They are native to China, according to University of Florida horticulturists Joan Bradshaw and Sydney Park Brown, where the plants have been cultivated for more than 1,000 years. Gardenias are desirable for their attractive form and fragrant flowers, but they are not hardy shrubs. These plants require careful and thoughtful care.
Keep It Warm
Gardenias are warm-climate plants. They thrive in United States Department of Agriculture (USDA) growing zones 8 through 10. Gardenias enjoy exposure to full sunlight and daytime temperatures in the low 70s Fahrenheit, with a drop of 10 degrees at night. If you live in a climate that has temperatures that dip to freezing, consider growing the gardenia as a houseplant, or choose a variety that has been cultivated to withstand cold temperatures, such as "Kleim's Hardy."
Keep It Wet
Gardenias need humidity in the air and water in the soil to bloom properly. Bud drop, which occurs when the buds drop off the plant before opening, is a symptom that the plant is not getting enough humidity or water. Avoid misting the plant with a spray bottle, as wetting the foliage can lead to the development of fungal diseases such as root rot. Instead, place indoor plants on a humidity tray if it's potted (a tray filled with pebbles and water), or run a humidifier near the gardenia. For outdoor plants, make sure the soil around your gardenia is consistently moist. This also holds true for indoor plants.
Use Good Soil
Gardenias thrive in soil that is well-draining but rich in organic materials. Work a large amount of organic mulch into the soil around your plant. If the soil is heavy, like clay soil, amend it with peat moss to aid in water drainage. Ground bark can also be added to the soil, according to Marjan Kluepfel, a horticulturist with Clemson University.
Gardenias are heavy feeders. Some home gardeners plant these shrubs carefully, in a sunny, protected location, then neglect to feed them. Fertilize your gardenia at least two times a year. Kluepfel suggests using an acidic fertilizer, such as fish emulsion. Feed the shrub in mid-March, then again at the end of June. Do not feed in the fall, as this will stimulate the gardenia to produce new growth that can be killed by cold temperatures. If your gardenia is indoors, however, you can fertilize it again in September.