Answer: You can allow your gardenia to enjoy the summer outdoors, but you'll want to take it inside before nighttime temperatures drop into the 50's this fall.
Your challenge in growing the gardenia indoors is to match the plant's native environment as closely as possible. First, make sure you give the plant plenty of bright light, preferably direct sunshine, for at least half a day. Winter will likely be the most difficult time to keep high light intensity due to short, gloomy days. Moving plants closer to southern-exposure windows and/or supplementing with plant grow lights will help.
Gardenias thrive in moderately humid air, but maintaining proper relative humidity is a challenge, particularly during the winter heating season. There are several ways to help increase humidity, including running a humidifier and grouping plants together on trays of wet pebbles. Misting by hand with a spray bottle offers only momentary relief and does not really increase humidity in a meaningful way.
A healthy, blooming gardenia will need to be nurtured with a steady supply of water and nutrients, but don't overdo. The goal is to provide the proper balance of water, air and nutrients. If soils are kept constantly wet, the roots can be starved for air. Too much fertilizer can lead to damaging salt accumulation. Monitor the soil frequently for moisture content, and water thoroughly as the top inch of soil dries. Use a fertilizer formulated for acid-loving, blooming plants, such as an azalea-type product, according to rates listed on the label.
Don't be afraid to prune the gardenia. In fact, blooming will be more prolific on younger growth. Remember that the gardenia is a woody shrub in its native environment and may need to have older, woody stems removed to make way for new branches. Keep a pair of hand pruners indoors to keep the gardenia rejuvenated.
Keep an eye out for insect pests. If caught early, they can be controlled with insecticidal soaps or other products that are specifically labeled for use on indoor plants. A cotton swab dabbed in rubbing alcohol also will help control a small pest population. You may feel overwhelmed just thinking about all of these responsibilities. However, if you persevere, the gardenia will reward you with masses of stunning white blossoms accompanied by an elegant fragrance that simply cannot be matched by other plants.
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