The abundant creamy white flowers and rich, glossy green foliage make gardenias a very popular ornamental shrub found in America's far south and southern west coast. In cooler climates they are kept as house plants and sometimes left outdoors in the warmer months. Originating from China, there are more than 200 species of gardenia with some reaching 6 to 8 feet in height. Among gardeners, gardenias have a reputation for being somewhat temperamental, requiring constant care and attention to keep them blooming and healthy.
Plant gardenias in direct sunlight or partial shade in well-drained soil. These plants need acidic soil with a pH range of 5.0 to 6.5. Have a soil test done if you are unsure of the pH level. Naturally alkaline soil will need constant amendment to make it suitable for gardenias.
Add several inches of mulch around your gardenia, and water thoroughly twice a week for first several months after planting. After the plant is established, keep the soil moist but not saturated. Gardenias prefer moist air and some gardeners use misting systems effectively to maintain elevated humidity.
Feed the plants with an acid-forming, balanced fertilizer that is 50 percent slow release. Applications should be given in spring, late summer and late fall.
Prune gardenias after they have finished blooming for the season. Pinch stem tips to encourage plants to fill out, and remove deadwood from the interior of the plant to improve air and light penetration.
Examine your plants often for signs of insect infestation. Gardenias are prone to insect problems, attracting mealy bugs, aphids, spider mites, scale and white flies among others. Early detection and treatment of any infestation is essential to prevent serious plant damage. Horticultural oil, neem oil, mineral oil and insecticidal soaps are effective against most insects.
Place gardenias in full sun, and keep room temperature at 68 to 70 degrees Fahrenheit by day and 60 degrees at night. Use a sterile potting soil with added peat moss to increase the amount of organics. Gardenias need at least moderate humidity. If the air in your house is constantly dry, buy a humidifier to regulate the moisture of the air near your plant.
Water indoor gardenias when the top inch of soil is dry. Make sure the planting pot has drainage holes and a tray so that roots are not standing in water.
Fertilize in spring and summer with a balanced, slow-release fertilizer formulated for acid-loving plants.
Prune house plants as needed after flowering to create and maintain shape. Stimulate new growth and lateral spread by pinching stem tips and removing excess woody branches.
Check often for insect or disease problems, and apply appropriate treatments. Many plant diseases affect gardenias, and you should seek advice from local horticulture professionals concerning any unusual growths, molds, spots or other abnormalities.
About this Author
Based in Surrey, British Columbia, Stephen Oakley is a freelance writer focusing on environmental issues, travel and all things outdoors. His background includes many years spent working in the Canadian wilderness and traveling worldwide.