Grow gardenias in a compost for acid loving plants. Gardenias can be grown in beds, but growing them in containers allows the plants to be moved to more suitable seasonal sites and makes it easier to control pests.
Over summer, place in a light situation but shade from direct sun, as the plants may be scorched or the leaves may wilt, even if the compost is moist. A west-facing window sill is ideal. Night temperatures should remain as far as possible between 15–18°C (59–65°F) with a day temperature of 21-24°C (70-75°F) as fluctuations can damage flower buds. Ventilate to reduce the temperature and provide a free airflow but without draughts. Bright light is needed but hot direct mid-day sun should be avoided by careful positioning or by some shading of glasshouses and conservatories.
In winter, place the plant in as much light as possible such as in a south facing window of a heated conservatory or glasshouse. Provide a minimum temperature of 16°C (61°F) if possible, although 10–15 °C (50–59 °F) is acceptable.
Watering and feeding
Gardenias grow best in conditions of high and uniform humidity. Stand the container on tray of gravel, expanded clay granules (Hydroleca) or recycled lightweight aggregate (Hortag) and keep moist, with the water level slightly below the surface of the gravel. Mist the leaves frequently in hot weather, but not when in flower, as water on the flowers may discolour them.
Over spring and summer keep the compost moist, but not saturated. Over winter, when the plants are not growing, reduce the watering, without allowing the compost to dry out between watering. Use rainwater where possible, and always at room temperature.
Gardenias require high nutrient levels from six weeks after potting; use a high nitrogen liquid feed every week in spring and summer. Over winter, feed with a balanced fertiliser with trace elements at five or six-week intervals.