How to Grow Gardenias Outside in Containers

Fill the container with a peat-based soil mix without lime. The gardenia requires acidic soil, with a pH in the 5.0 to 6.5 range. Make your own by combining equal parts of ¼-inch chunks of ground bark, peat moss, azalea potting soil and one handful of soil sulfur.

Avoid transplanting the gardenia into a larger pot because it is potbound. The plant thrives and blooms best under this condition. When roots show through the pot's drainage holes, transplant the gardenia into the next larger-size pot.

Move the pot into a shady location during the afternoon.

Fertilize the container-grown gardenia once a month with an acid-based fertilizer, such as azalea fertilizer, according to the package instructions. Although it is safer to purchase a fertilizer labeled "for acid-loving plants," suitable fertilizers include 6-4-4 and 11-7-7. Water the soil before and after the application.

Water the outdoor gardenia to keep the soil slightly moist. Don't allow the container to sit in a tray of water -- empty it 15 minutes after watering the plant. Gradually reduce the amount of water given the gardenia in winter, as it goes dormant. Water the plant when the soil's top is dry.

Pinching 1 inch off the tips of new stems encourages the gardenia to grow bushier. Clip or pinch off flowers when they die. If you need to prune the gardenia, do so after the summer blooming period.

Bring the gardenia into the house if you live in a region with cold winters. Give it four hours of direct sun every day. Water it only when the top inch of soil is dry and withhold fertilizer until it begins growing again in spring. The ideal room temperature is between 60 and 65 F at night 65 to 70 F in the daytime. Place a humidifier near the gardenia for the winter's duration.