Gardenias, which are semi-tropical plants, grow best in warm, humid areas with an abundance of sunlight. It is hardy in growing zones 8 through 10 and grown as a houseplant in all other zones (see resources for growing zone information). The fragrant, waxy flowers bloom from mid-spring into summer and have an intoxicating scent. Gardenias can be temperamental plants so it's important to learn a few basic growing tips.
Temperatures and Soil Conditions
Daytime temperatures need to be around 65 to 70 degrees Fahrenheit. Nighttime temperatures should be no lower than 60 degrees Fahrenheit. It may be best to grow gardenias in containers so they can be brought in at night or during the winter months.
Gardenias like lots of sunlight, although some shade in the warmer summer months is tolerated. If growing a gardenia indoors, make sure it gets plenty of sunlight by placing it near a large south-facing window or in a sun room.
Use an acidic, well drained soil with a 5 to 6 pH. Add peat moss or compost to enrich the soil.
Over watering is the biggest problem with gardenias. The leaves will start to turn yellow if they are receiving too much water, and if they become too dry the leaves will begin to droop and wilt. Stick your finger in the soil about 1 to 2 inches to test for moistness: If it's moist do not water.
If growing gardenias inside, be sure there is enough humidity to keep the plants from drying out. This can be done by placing the potted plant in a tray filled with 1 inch of pebbles or stones and adding water. (The water should not cover the pebbles.) You can also place a humidifier in the room with the plant, but do not mist it. Humidity reduces red spider mites, which are a common pest on indoor plants.
Fertilizing and Pruning
Fertilize gardenias in March and again in late June. Do not feed in summer when new growth is forming, because it will make the plant more susceptible to cooler temperatures. Use a rhododendron or azalea plant food to fertilize gardenias. Spread out about 2 to 3 inches from the base of the plant.
Finally, prune your plant after flowering in early to late summer. Remove old wood and spent blooms. This is also the best time to shape your plant. Do not prune in the spring. Gardenias flower in the spring and summer and grow on old wood, meaning that its buds form on growth that occurs after it's done flowering. Pruning in the spring will cut off that growth.