In the Garden > Flowering Plants & Shrubs
Gardenias are an outstanding flowering shrub with an exquisite perfume that creates a magical, romantic atmosphere in the garden. They flower at their best in the warmer months of the year usually from November to May. Their large creamy white flowers and glossy green leaves also make them very attractive garden plants.
Don Burke awarded John and Carmen Shaw's garden the inaugural Burke's Backyard gardening excellence award because the gardenias in their garden were the best he had ever seen. What is their secret to growing such healthy gardenias in an area that is not ideal for this semi-tropical plant? The location is subject to frost with winter overnight temperatures falling to -4°C. The owners have created a microclimate around the house so that the plants would not get frost-bitten in winter. The house is brick and there is extensive brick paving which absorbs the heat from the sun during the day and radiates it out at night creating a frost free zone. (See diagrams).
Agricultural piping was laid throughout the garden before major works began thereby ensuring excellent drainage. As well as that, the gardenias were planted in raised garden beds with an irrigation system installed so that the sprinkler heads were underneath the foliage of plants. Undoubtedly the most important key to the success of the gardenias is their nutrition. The area was previously a dairy farm which was heavily fertilised to ensure constant grass production for the cattle. Nutrients were also recycled in the form of manure.
The existing richly fertilised soil was then made even richer by the addition of a special soil mix from Australian Native Landscapes (ANL). To every four parts of ANL's standard organic mix they added one part of duck litter and one part of mushroom compost. The organic garden mix itself is made up as follows:
As you can see, this is an incredibly rich mix. The mix was added throughout the garden to a depth of at least 200mm (8"). This had the effect of raising the height of the beds.
In addition to the rich soil, once the gardenias were planted they were fertilised yet again with a slow release fertiliser, Multicote by Haifa Chemical Ltd ( N:P:K 18:2.6:9.9) 8-9 month release fertiliser. During the early establishment the plants were watered several times per week but since establishment are only given a good soaking once a fortnight via the well designed irrigation system. The plants are fertilised with Multicote each spring and again during summer. The plants are growing in full sun through to part shade.
It is generally believed that an acid pH is critical in order to grow good gardenias. The Shaw's soil tested at pH 6-7 which is only slightly acid. In summary the conditions in the Shaw's garden provided excellent drainage, warm microclimate, rich organic soil, regular deep watering and lots of fertiliser. These conditions are similar to those in nurseries where potted gardenias are grown.
Common name: Gardenia, Florist's Gardenia.
Botanic name: Gardenia augusta. The most commonly grown variety is called 'Florida'.
Other varieties: 'Prof. Pucci', 'Fortuniana' and 'Magnifica', which have larger flowers. 'Golden Magic', which has flowers that turn yellow with age. 'Radicans' is a dwarf form with a prostrate habit (up to 0.5m high by 1.5m spread or 20x50"), making it an excellent ground cover. It has smaller flowers and leaves and tends to have more cold tolerance than 'Florida'. 'Aimee Yoshiba' is a newer variety which has large deep green leaves and is said to be the best of the larger flowering gardenias.
Other species: G. thunbergia (the star gardenia) has a tubular flower and more cold tolerance than the G. augusta. It is a native of South Africa. It is a better choice for Adelaide and environs.
Climate (see map): Gardenias are warm climate plants which are at their best in a mild, humid climate. They are seen to perfection in frost free areas north of Sydney and Perth but will grow in Adelaide and Melbourne in a warm spot. The gardenia is native to eastern Asia (China, Taiwan and Japan).
Frosts and cold climates although as seen in the Shaw's garden, warm microclimates can be created in frosty areas.
Downside: As with all popular plants there are some common problems with gardenias.
Readily available in pots at nurseries, particularly during spring and early summer when plants are in flower. Prices range from $8.95 for 150mm (6") pot. $14.95 for 200mm (8") pot and $30.00 for 250mm (10") pot. A 1.5m (5') standard gardenia will cost $80 - $120.
Multicote fertiliser is available from Elders throughout Australia. Cost is $24.75 for 4 kg and $90.20 for 25 kg.
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