To grow gardenias, test the soil, and amend the soil so that the pH is between five and six. Choose a sunny or partially shaded location, work compost or peat moss into the soil, and plant the gardenias 3 to 6 feet apart. Provide the plants with 1 inch of water per week, and cover the soil with a layer of mulch to maintain moisture levels. After the blooms wither, deadhead them to encourage new growth.
Water gardenias more frequently during dry, hot weather, and maintain high humidity levels when growing the plant indoors. To raise humidity levels, use a humidifier in the room where the gardenia is located, or place the plant and its container on a tray that contains pebbles and water.
Fertilize gardenias at the beginning of spring and at the beginning of summer. Choose an acidic fertilizer that contains chelated iron and nitrogen to promote healthy growth. To produce a bushy plant that blooms heavily, pinch back the tips of the plant when it is dormant.
Place a potted gardenia in an area with bright, indirect sunlight, and maintain temperatures of 60 to 70 F to ensure the plant produces flowers. Remove spent blooms and dead wood in the autumn, and trim the plant to the desired shape when it is dormant.