FIVE TIPS FOR GROWING GARDENIAS 1) Keep the soil moist, making sure gardenias get at least an inch of water a week. 2) Deadhead (cut dead blooms) to encourage more flowering. 3) Use an insecticidal soap or horticultural oil to prevent pests, such as white flies and mealybugs. 4) Remember that high humidity is essential, but keep the shrubs partially shaded. 5) Apply 2 to 4 inches of organic mulch to keep the soil moist.