Gardenias grown indoors should receive at least 6-8 hours of direct sunlight through a sunny window. Make sure your Gardenia soil is moist and well-drained. Gardenias need at least 1 inch of rain (or equivalent watering) each week. Keep the soil consistently damp but not soggy.
Gardenias use a lot of nutrients to produce so many glorious blossoms. Feed your shrubs by applying an acidic, slow-release fertilizer such as an azalea or camellia fertilizer. For the organic gardener, blood meal, fish emulsion or bone meal work well.
Light. Gardenias need at least four hours of sunlight daily (most blooming plants have basically this requirement, although there are exceptions). Without at least this much light, they just won't bloom. However, in our fairly brutal summer heat, some afternoon shade will protect the gardenia's foliage from burning.
Gardenias perform best in day temperatures of 65-70°F (18-21°C) and night temperatures of 60-65°F (15-18°C). Flower buds will fail to form if the ideal temperature for Gardenias is not respected! Gardenias demand high humidity to thrive.
If you're growing your gardenia in a pot, repotting every 2 to 3 years is prescribed. The plant needs space to grow, and a tight pot would alter its development. Wait for the plant to show it needs more space before repotting. Best repot the gardenia at the end of winter or at the beginning of spring.