A short guide to growing Gardenias

Gardenias are favourites in subtropical gardens, loved for their highly perfumed white flowers and glossy leaves.

Gorgeous: a Gardenia flower. Photo: Alamy

Gardenias are favourites in subtropical gardens, loved for their highly perfumed white flowers and glossy leaves. The most common, and still one of the best, is Gardenia ‘Florida’, a medium shrub with prolific flowers. But there are about 130 species in the genus, including some small trees. They come from tropical and sub-tropical regions of Asia, Africa, the Pacific islands and Australia’s Top End.

Our few native Gardenia species are rarely seen in cultivation. But confusingly, what we call native gardenia (Atractocarpus fitzalanii) is in a different genus, although within the same Rubiaceae family. This lovely small tree, also called yellow mangosteen, is a bush tucker plant from Far North Queensland. The white, star-shaped, fragrant flowers in spring develop into brown fruit that ripen slowly over winter. It can reach 6m tall or be pruned to shrub size, and even kept in a pot.

Among the shrubby gardenias, there’s plenty of choice. Gardenia ‘Florida’ (about 1m x 1m) has smaller flowers than some others but they’re produced in abundance over many months. ‘Magnifica’ is the tallest variety at 2m, with extra large flowers and leaves. ‘Aimee Yoshiba’ also has large blooms but is 1.2m-1.5m tall, as is ‘Professor Pucci’, whose big white blooms fade to yellow. ‘Radicans’ and the similar ‘O So Fine’ are low, spreading forms, with narrow leaves and petite flowers. More recent varieties have simpler, single rather than double, flowers. ‘Grandiflora Star’ and ‘Star’ are compact bushes about 50cm tall, whose flat, white petals fan out in a star shape. ‘Super Star’ has masses of pinwheel flowers on a 1m shrub. A more unusual species is tree or star gardenia, G. thunbergia, from South Africa. Reaching 2.5m-3m tall and wide, it has horizontal, spreading branches bearing sweetly perfumed, white, flattish flowers from late spring into summer.

Not everyone has success growing gardenias because of their particular needs. Outside the tropics and subtropics they can be challenging. In cooler climates, gardenias need a warm microclimate sheltered from cold winds and frost. In summer-dry areas, they need additional watering and protection from the hottest sun. Despite labels that claim they grow in shade, without enough sun gardenias will be sparse and spindly, and won’t flower. The soil should be well drained, slightly acidic, and rich in organic matter; protect their shallow roots from drying out with mulch. To keep plants bushy, prune in early spring before the flower buds begin to form.

Q&A

How can I kill the Italian arum lilies that dominate my small garden? Digging them out over several years has proven fruitless. Simon Cox, by email

Italian arum (Arum italicum) loves shade and moist soil. It can be difficult to control as it reproduces from both the tuberous roots and red berries. All parts are poisonous and irritating to the skin. Spray young foliage with glyphosate (Roundup, Zero). Alternatively, smother it with thick sheets of newspaper covered with mulch.

When should I start pleaching my row of lemon myrtle trees, planted six months ago? They’re 1.3m tall; I’d like a 4m-5m-tall hedge. Louise Deakin-Bell, Sydney

Pleaching involves bending and training the lateral branches of closely spaced trees with clear trunks to produce a “hedge on stilts”. It provides high screening while leaving space, light and air around the bottom 1.5m or so. Once the trees reach the height you want the hedge to start, cut the tops of the central leaders, then start to remove the lower branches. Train side branches along horizontal wires or bamboo scaffolds and prune off forward-growing shoots.

Eco-Organic Garden range

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. The best question for October wins a hamper of organic products from Eco-Organic Garden worth $110.