AUSTRALIAN NATIVE HIBISCUS
Although new species of hibiscus and hibiscus-like plants are still being found and recorded (1), the beauty of at least one species was recognised as long ago as 1828. The Colonial Botanist of New South Wales, Charles Fraser described Hibiscus splendens as the King of all the Australian plants he had seen. He described the flowers as being the most delicate pink and crimson and literally covering the plant. Hibiscus splendens is just one member of the Hibiscus family. Australian representatives may be herbs, shrubs or trees and include Abelmoschus, Abutilon, Alyogyne, Gossypium, Lagunaria, Malva and Radyera and of course Hibiscus.
These plants vary in size from a ground cover, Abelmoschus moschatus ssp tuberosus, to small plants such as Hibiscus trionum (0.2 m) , to medium shrubs such as Alyogyne huegelii (1-2.5m) and tall trees such as Lagunaria patersonii (to 13 m). Not only is there a range of sizes but members of this family can be found growing in tropical areas, for example, Abelmoschus manihot; in swamps and crater lakes, e.g. Hibiscus diversifolius; along the beach, H. tiliaceus and Thespesia populnea; in inland Australia, e.g. Gossypium sturtianum, Alyogyne hakeifolia; in fissures in sandstone, in open forest or along rainforest margins, H. splendens; and along the margins of light rain forests on soils ranging from loam to granitic or poor and gravelly, H. heterophyllus. While most species occur in subtropical and tropical regions, some species can be grown in temperate climates which have irregular rain in summer and reliable rain in winter, e.g. Hibiscus splendens (2) and H. diversifolius if kept well watered (3). Other species can be grown in warm temperate zones where there is mainly reliable rain in both summer and winter e.g. Alyogyne hakeifolia, A. huegelii, Hibiscus heterophyllus and H. tiliaceus (2). Hibiscus plants grow even under tough conditions, e.g. remnant stands of Hibiscus heterophyllus growing on hillsides near Brisbane show no adverse effects from drought and roadside plants of H. divaricatus re-grow after being burnt. One species, Alyogyne huegelii, has been described as thriving in the most desolate of places (4).
Depending on the species, flowers may be white, various shades of yellow, pink, purple, or red. Most plants are perennials, even though plants such as Abelmoschus moschatus die back for part of the year. Hibiscus trionum is usually treated as an annual species. Flowering times vary according to the species but in a subtropical climate such as Brisbane, by planting a range of species, it is possible to have plants flowering throughout the year. This prolonged flowering and the production of nectar contributes to the value that Hibiscus species have for "faunascaping" (5). Not only will blooms which produce nectar feed nectar-eating birds and predators but they will also attract insects for insect eaters, provided there are protected water sources and nesting places for birds. In addition, the seed capsules of species such as H. heterophyllus can provide for seed-eaters. Thus, apart from any aesthetic appeal of birds and insects, plants such as hibiscus species which attract birds and predators encourage natural pest control as the insects use the plant as a food source and are themselves controlled by a wide range of predators (11). Honeyeaters take advantage of the large nectar-rich flowers of species such as Alyogyne huegelii, Hibiscus diversifolius, H. heterophyllus (6) and H. splendens (7). Birds such as lorikeets are attracted to species like H. heterophyllus (6) and the sight and sound of a Hibiscus heterophyllus literally covered with lorikeets bowing down the branches as they feast upon the seed capsules more than compensates for any damage sustained. Insects seek out the flowers of H. diversifolius, H. heterophyllus, H. splendens and H. tiliaceus (5) and H. tiliaceus is a butterfly food source (8).
HIBISCUS IN GARDEN DESIGN
Given the range of sizes, variety of habitats, range of soil types, widespread distribution and potential for "faunascaping", Hibiscus and Hibiscus-like plants could enhance most garden styles.
Four ways of incorporating Hibiscus plants as a means of enhancing the garden will be described. The suggestions, are as a screen, as a feature, as part of a mixed planting or as a container plant.
HIBISCUS AS A SCREEN
Two rapidly-growing species, Hibiscus heterophyllus and H. splendens, occur on the coastal strip north from Kiama with H. heterophyllus being found as far north as Cooktown and H. splendens to Tully, as well as in central Queensland (27). Both grow as shrubs or small trees and form a screen. The prickles that are usually found on the branches become a plus when used this way, although if they are a problem, or if a salt resistant plant is required, Hibiscus insularis could be grown. If allowed to grow without pruning, the bushes will not retain foliage to the ground but will provide a dense screen from about 1.5 metres up. For a screen of H. heterophyllus, H. divaricatus or H. insularis, the lemon form of H. diversifolius is useful between the taller plants. When the screen is the pink form of H. splendens, the pink form of H. diversifolius provides a low-level screen. From the New South Wales border north, H. tiliaceus grows as a spreading tree that can grow as tall as 9 m and spread as wide as 16 m. H. diversifolius grows well underneath and the flowers go well together. For inland gardens, Gossypium species such as G. sturtianum can provide a screen approximately 1.5 m. For a formal garden, the pyramidal shape of Lagunaria patersonii could be used in Sydney and areas north of there for a tall screen and H. insularis makes a good hedge plant and windbreak (13) where a lower screen is required.
HIBISCUS AS A FEATURE
Most styles of garden could accommodate Hibiscus and Hibiscus-like plants as features. In Brisbane, Hibiscus heterophyllus makes an attractive specimen plant (6) and plants of H. tiliaceus which have been developed as standards, are used to provide shade in car parks such as at the airport and in some shopping centres. In Sydney beach-side suburbs (28), and in parts of Brisbane, Lagunaria is used as a street tree, although care should be taken as hairs on the fruits cause skin irritation. However, almost any species could be used, in almost any style of garden, as a feature plant, particularly if there is repetition of the same species. All species flower prolifically and many have unusual foliage, e.g. Alyogyne huegelii, Hibiscus splendens. Where the foliage is not distinctive, the flowers usually show up well against the foliage, e.g. H. heterophyllus, H. diversifolius.
For a formal garden, plants which respond well to pruning could be included, particularly species which can be trained on clean trunks such as H. heterophyllus and H. splendens (10). Plants which naturally grow into particular shapes may have a role e.g. Lagunaria patersonii grows into an attractive pyramidal shape and Hibiscus insularis requires only light pruning to keep a rounded shape (11).
HIBISCUS IN A MIXED PLANTING
This is where interesting results can be achieved. Whatever the colour of the hibiscus, there are many possible combinations of Australian plants. Plants chosen can complement the hibiscus bloom or provide a contrast. Plants such as grevilleas which attract birds are particularly useful as the birds can be seen harvesting pests such as scale on the hibiscus. Grevilleas are available in all the colours of both species hibiscus and currently existing cultivars: white, various shades of yellow, apricot, pink, red and maroon.
HIBISCUS AS A CONTAINER PLANT
Almost all species can be grown in a pot. If a seedling is grown, not only might the flowers be a long time coming, but it will be difficult to maintain the plant in a pot. If cuttings are taken, instead of the tap root system of a seedling, the plant has fibrous roots and is then much more amenable to being contained in a pot, particularly if the plant is tip-pruned from the earliest stages. The result is a bushy plant that flowers freely and much earlier than it would as a seedling (13). Plants can be potted on until the desired size is reached and then maintained at that size by pruning. Species such as Hibiscus heterophyllus, H. divaricatus and H. splendens can be maintained as small plants in small pots or allowed by potting on to reach a height and/or width of 1.5-2m depending on the way they are pruned. If allowed to become straggly and then pruned heavily, flowering may be reduced for that season but the plant will soon produce new growth. This new growth should be tip-pruned. Smaller species do not require any pruning. Abelmoschus moschatus "Mischief" flowers heavily in a pot without pruning as does Hibiscus trionum "Sunny Days". By having a range of species in containers, e.g. Abelmoschus manihot and A. moschatus, H. heterophyllus, white and yellow forms, H. divaricatus, H. splendens with varying shapes of foliage and in various shades of pink, H. diversifolius, lemon and maroon forms, Hibiscus insularis, Alyogyne huegelii and A. hakeifolia and Gossypium sturtianum, it becomes possible to move plants to provide a feature, e.g. Abelmoschus moschatus "Mischief" produces bright red flowers at Christmas time in Australia.
HIBISCUS AS A FOOD PLANT
Those interested in useful plants may enjoy exploring the many advantages of Hibiscus and Hibiscus-like plants. The flowers, leaves and even the roots are described as edible (15,16,17,18,19,20). Although it has been argued that no hibiscus is known to be poisonous and that it is probably safe to eat any that taste acceptable (14), caution should be exercised. Before eating any plant, be sure plants are accurately identified, take care with unfamiliar foods and be aware that even although hibiscus is usually considered safe, adverse reactions in particular individuals cannot be ruled out. The flowers make an attractive, edible garnish for salads. The petals of Hibiscus heterophyllus make a delicious preserve. One species, Abelmoschus manihot has leaves that are high in protein (21,22) and is an important vegetable in countries such as Papua New Guinea. There are other uses beside food. Fibre can be produced from the bark of species such as Hibiscus tiliaceus. H. tiliaceus and Thespesia provide wood for a variety of purposes (13).
|Hibiscus tiliaceus/Talipariti tiliaceum|
CHALLENGES ASSOCIATED WITH HIBISCUS IN GARDEN DESIGN
Although Hibiscus can enhance the 'native' garden, Hibiscus species are not without problems.
Susceptibility to frosts has to be considered, although most are hardy plants in areas where only light frosts are experienced (28). Species such as Gossypium australe and G. sturtianum are frost resistant (29) however species such as Hibiscus heterophyllus and H. splendens will need extra protection in frost-prone areas (8) but can grow well in frost prone areas against a wall or fence (30). Even after being severely burnt by frost, species such as Hibiscus heterophyllus, H. divaricatus and H. splendens may reshoot, either from the lower sections of the trunk or from ground level. It appears to be possible to lessen frost susceptibility by careful selection of hybrids, for example several of a number of hybrids between H. heterophyllus and H. splendens have survived frosts that have damaged the naturally occurring species growing on the same site. Both Hibiscus tiliaceus and Thespesia populnea may reshoot from the base of the trunk after being burnt by frost. The foliage of Alyogyne huegelii may survive frost but plants that have experienced frosts may lose all buds and flowers present at the time of the frost.
Another difficulty is that in some species such as Hibiscus diversifolius, H. heterophyllus, H. splendens and Abelmoschus manihot, the seed pod is covered in hairs that may cause severe skin irritation. Sticky tape stuck onto the skin and then pulled off appears to be the easiest and most effective way to remove these irritant hairs as well as wearing gloves and using tweezers when extracting seed.
There are a variety of sucking or chewing creatures that enjoy the flavour of both buds and leaves, although well grown plants are less likely to be attacked by either pests or diseases (13) and control is usually not warranted, especially if it is appreciated that many pests represent an important food for birds and predators and if the garden already has birds and other predators present to clean up most pests (31). Hibiscus beetles mostly feed on the pollen of the hibiscus flower and may chew holes in the petals (9). Even though Harlequin bugs depend on the sap they suck from species such as hibiscus, the damage is rarely serious (9) and their colours are so spectacular that they can even be considered desirable (10). Scale insects can become a problem but can be easily managed either by removing by hand or even by cutting off affected parts. Any other damage that may occur can also be pruned off. Regrowth is so fast after pruning the plant may actually be improved.
Pruning to maintain a desired size or shape may be seen as a chore. While pruning is unnecessary for plants used for screening, or as understorey plants or in the rainforest, it appears that pruning species such as Hibiscus heterophyllus, H. divaricatus and H. splendens by one third at the end of the flowering season may lengthen the life of the plant. For container plants, ongoing tip-pruning and pruning after flowering is recommended or the plants soon outgrow the container. The plant repays the effort of pinching out tips and pruning as the result is a more compact plant with a much greater number of flowers.
Probably the major obstacle to incorporating Hibiscus and Hibiscus-like plants is availability of plants. Even in Australian, few nurseries regularly carry Australian species. Charles Fraser recognised the merit of the Australian species he so admired as he sent seeds of H. splendens to the Royal Botanic Garden, Edinburgh. However, over 150 years later, despite their adaptability and ready flowering, this same plant and many of its close relations are not yet readily available or if available may be incorrectly or inadequately identified. The difficulty with obtaining plants is likely to continue until the landscaping potential of this long ignored family of plants finally begins to be recognised.
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