Gardenias like a warm position. This is probably the single most important thing to remember when growing them in Melbourne. An east-to-north facing spot that captures sun till mid-afternoon is ideal. Against a brick wall or in a small courtyard that traps heat is also a good position. While they like heat, very hot afternoon sun can yellow leaves, so protection from the west (in summer only) is necessary. They are well-suited to being grown in pots and then can be easily moved around if there isn’t an ideal spot for them in the ground. Cold winter temperatures make leaves yellow and shed, particularly the older central leaves.
Gardenias like acid soil, so add plenty of compost or manure to the soil. Most potting mixes are usually slightly acidic. Feed twice a year as they come into bud in spring, and again after they finish flowering around December/January. Magnesium sulphate (Epsom Salts) helps to acidify the soil and prevent some yellowing of the leaves, as gardenias are a bit susceptible to magnesium deficiency. If new growth goes yellow to white, feed with chelated iron. Harry’s Gardenia Food is an excellent ertiliser specifically for Gardenias, to help keep them green and flowering. Results are impressive!
Shrubs should be pruned immediately after flowering and then fed with a high nitrogen fertiliser such as Harry’s Gardenia Food to promote autumn leaf growth. If they become very leggy, gardenias can be heavily pruned back to the old wood to make them bushy again. Mid spring is the best time for this, even though flowering may occur later in the summer than normal.
Aphids, thrips or mites can distort flower buds and new growth. Spraying with pyrethrum helps control these pests. Dropping of buds can be caused by lack of food (potash), but more commonly, it is due to cool or fluctuating temperatures in spring. Again, a warm spot is the best cure. Irregular watering can also be a factor. Scale can be controlled using products such as Pest Oil, Success or Eco Oil.
Medium grower, smaller leaves and flowers than some varieties but the hardiest in Melbourne.
Small-leafed, horizontal, rockery gardenia, good for pots, even hanging baskets. Needs warm spot.
(Golden Magic) Taller growing, more spectacular varieties with big glossy leaves and larger flowers. A bit more temperature-sensitive in Melbourne.
Gardenia thunbergia Tree gardenia, medium shrub, quite hardy in Melbourne. Single tubular flowers, very beautiful but difficult to obtain. Specimen in Burnley Gardens and a hedge on the east side of the Botanic Gardens.
Occurs naturally through the colder months, so don’t worry in mid to late winter. Gardenias sometimes take a few years to settle into a new position, so persevere. Nitrogen & magnesium (Epsom Salts) in spring helps to stop yellowing. They are heavy feeders when setting bud, so apply Harry’s Gardenia Food for best results. A warm spot is the best cure for yellowing leaves. Feed with a liquid fertiliser every 4-6 weeks (even through winter) to help to avoid yellow leaves.