Growing gardenias as houseplants requires specific conditions. The gardenia jasminoides is a finicky, woody perennial shrub native to Asia. The plant can grow outside in the southern United States, but it is often available as a houseplant. Though a gardenia requires a higher level of care than the typical houseplant, the fragrant white blooms reward the vigilant caretaker. Dark green foliage with high gloss set off the roselike flowers and provide year-round appeal.
Repot the gardenia after it finishes flowering. Use a lightweight potting mix that drains well. Increase the planter size when the plant starts to become root-bound and the soil dries out quickly. A 2-inch increase or more gives the plant room to grow.
Fertilize with an acidic fertilizer high in nitrogen suitable for flowering plants, such as an azalea fertilizer. Apply the fertilizer to the gardenia every two weeks in the spring and summer.
Provide nighttime temperatures between 50 and 60 degrees Fahrenheit. This allows the plant buds to set; they will not set at higher temperatures. The gardenia needs daytime temperatures approximately 10 degrees warmer than at night. The ideal temperatures are 60 degrees at night and 70 degrees during the day.
Supply four to six hours of bright light per day. A sunny window or fluorescent grow bulb works well. Watch that the heat of the window does not cause damage and move the plant to a cooler location in the warmer months. Turn the gardenia every week so all sides benefit from the sunlight. Gardenias also need 14 hours of night conditions for flowering.
Keep humidity levels between 50 and 60 percent. Gardenias thrive in humid environments. Increase your home's humidity by using a whole-house humidifier, a room humidifier where the gardenia grows or have a variety of houseplants with high transpiration rates (evaporation of water through the leaves). You can also use small indoor water fountains placed near the plant or place it on a tray filled with rocks and water.
Prune the gardenia houseplant back with pruners after it blooms. Pruning prompts new growth, and the flowers form on that new growth. Thin out old stems to make room.
Water the plant when the top inch of soil feels dry. Rainwater provides the best results. Do not use tap water if you have a water softener because the sodium is too high. Keep the soil evenly moist and do not let the plant sit in water.
Watch for insect damage and diseases. Gardenias have susceptibility to white flies, spider mites and scale. At the first sign of any problems, apply the appropriate treatment.