Gardenias are rather specific in their cultural requirements, and when their basic needs are not met, annual bloom can be minimal or skipped entirely. Gardenias require ample fertilization, bright filtered or indirect sunlight, specific overnight temperatures and ample moisture but not too much. Creating the optimal growing environment will help to induce a flowering cycle each year.
Position your gardenia plants in a location where they will receive bright filtered direct sunlight or bright indirect light. When grown indoors, give gardenias bright direct sunlight during the winter and spring months and bright indirect or filtered sunlight the rest of the year to prevent leaf burn.
Maintain daytime temperatures in the range of 68 to 74 degrees F and an overnight temperature of 60 to 62 degrees F to set buds for bloom.
Water your gardenias regularly to keep the soil moist at all times but not soaking wet. Water at the soil line around the root ball of the plant and never over the head of the plant to prevent leaf spot and disease.
Feed your gardenia once each month during the peak growing season from spring through mid-fall. Use an acid-rich formula complete fertilizer designed for gardenias, camellias or rhododendrons for garden grown gardenias such as a 30-10-10. Feed with a water-soluble balanced plant food such as a 10-10-10 when growing your gardenias as indoor plants.