Most of Southern California is ideal for growing gardenias because of its warm, sunny days and cool nights. However, the flower does require about an inch of water per week, which is sometimes scarce in this area, so proper watering is paramount in order for the plant to thrive.
Growing gardenias in Northern California is sometimes difficult because of the cool, overcast weather throughout large parts of the year. Still, there are a few gardenias that manage to flourish. Varieties such as the Chuck Hayes and Kleim's Hardy are popular in this area thanks to their ability to withstand cold.
Although it is not without its challenges, gardenias can be grown indoors. Sun rooms are ideal because exposure can be managed, but it is sometimes hard to keep humidity high, which is extremely important for healthy plants. Plants will likely need to be watered frequently, but lightly.