Plant of the month – Hibiscus
Whilst many gardeners think of the tropical versions of these garden beauties, there’s also varieties that can handle our cooler regions.
For most of us, when presented with images of beautiful tropical Hibiscus blooms, it’s not hard to hear the sound of Hawaiian music, visualise palm trees waving in the soft breeze, and feel the touch of cool water from gentle, rolling waves. Ah well, one can dream!
It’s interesting that we tend to associate the tropical Hibiscus with places like Hawaii or indeed any exotic Pacific Island, whilst the real origin remains a mystery to most gardeners.
The “Hawaiian” Hibiscus (Hibiscus rosa-sinensis) is presumed to originate from around southern China and Vietnam, but over time has become naturalised in many Pacific Islands, giving rise to its common name. (Some references cite Vanuatu as the origin)
Coming from and enjoying any tropical climate means that this species, and the many cultivars that have been bred over hundreds of years, grows particularly well in frost-free sub-tropical and tropical regions. However, Hibiscus rosa-sinensis (rosa-sinensis means “Rose of China”) can also grow well in a temperate region, provided some thought is given as to its placement in a garden.
Hibiscus rosa-sinensis is regarded as a medium to large evergreen shrub, with the species plant and its numerous cultivars growing to between 1.5m to 3.5m tall. The single red flowers of the original species are around 5-8cm across, quite small compared to the showy blooms of the modern Hawaiian hybrids, which can reach as much as 25cm in diameter! Modern colours range from red through to pink, orange, yellow and white, in single or double blooms. Flowers, mostly held upright or horizontally, with a few pendulous beauties, are borne singularly in the leaf axils of the current year’s growth and usually only last 1 or 2 days before closing at night and falling. In warm climates, flowering occurs from around December to early winter, sometimes continuing through winter in milder areas. In temperate regions, flowering may finish earlier.
H. rosa-sinensis and its cultivars like a compost-enriched, well-drained soil with plenty of summer water. They will thrive in a sunny, wind-protected position with some cultivars tolerating light frosts. They’re regarded as heavy feeders, so it’s best to fertilise with a balanced plant food (NPK 10-4-8) in spring and summer, ensuring they have plenty of water as well.
Pruning is best done around September (after any frosts), cutting back to buds on last year’s growth. Once these shoot, a light tip prune in October/November will produce lateral growth and more flowers for the coming season.
Aphids, mites and mealy bugs are the main sucking pests of hibiscus. Aphids and mealy bugs can be treated with a horticultural oil, sprayed during cool days or evenings. Mites are best dealt with using wettable sulphur. The hibiscus beetle is a major pest of the flowers, attacking the unopened buds by chewing holes, usually causing them to drop. A beetle trap, made from a white or yellow ice-cream container containing some soapy water will attract the little blighters and drown them. Pick up any fallen buds, put in a plastic bag and then the bin, as they will contain beetles and their eggs as well.
Inconsistent moisture will also cause bud drop.
Another species, Hibiscus syriacus (The Rose of Sharon), is a much hardier, deciduous shrub, originating from Korea and China. This species is much more suited to temperate climates, withstanding temperatures down to -10 C. There are many cultivars of this species, with most growing between 2.5m – 3.5m high. The blooms aren’t large as its tropical cousin, flat out reaching 8-10cm across. However, the colour range is outstanding, with hues including white, pink, red, magenta, violet and blue, many having a beautifully contrasting centre of maroon, red or crimson.
H. syriacus can handle a wider range of soils and climates than H. rosa-sinensis and is generally more tolerant of pests as well. The dreaded hibiscus beetle will still chew on many of the lighter-coloured blooms, so be on the alert as buds form.
Pruning of H. syriacus is usually performed in winter, with up to two-thirds of the annual growth removed to help the plant bush up for the first 3 years. Light pruning, as for H. rosa-sinensis, can be done after that.
Some great Hibiscus rosa-sinensis cultivars are: ‘Apple Blossom’, ‘Celia’, ‘Crown of Bohemia’, ‘DJ O’Brien’, ‘El Capitolio Sport’, ‘Full Moon’, ‘Lady Cilento’, ‘Mrs George Davis’, ‘Peach Blow’, ‘Ruth Wilcox’, ‘Sabrina’, H. schizapetalus (stunning pendulous flowers), ‘Vasco’, and ‘Wilder’s White’.
If you’re after Hibiscus syriacus cultivars, look for: ‘Blue Bird’, ‘Diana’, ‘Rosalinda’, ‘Aphrodite’, ‘Woodbridge’, ‘White Supreme’, ‘Helene’, ‘W.R. Smith’ and ‘Duc de Brabant’.
There are also a number of Australian native hibiscus varieties, usually cultivars of H. heterophyllus. They can be a little more drought-tolerant than their exotic cousins. Look for the ‘Aussie’ range, ‘Aussie Pink’, ‘A. Pearl’, ‘A. Delight’ and ‘A. Choice’, and ‘Citrus Mist’
Always check your local nurseries to see which varieties they have in stock – they usually only sell Hibiscus that will grow well in your region and climate.
There are many online suppliers as well but do your homework before purchasing to ensure their plants will grow in your patch.