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Exotic Plants
"The exotic vegetation that replaces indigenous plant communities in urbanising regions, disassociates us from the rhythms and diversity of the native landscape and a sense of the place; and we are the poorer because of it."
Michael Hough, Professor of Landscape Architecture, York University, Canada
According to Nursery & Garden Industry Australia, nurseries and garden centres sell 94 percent exotic plants and 6 percent natives.
We hope to live long enough to see these figures reversed: 94 percent native to the region in which they are sold, with the remaining six percent a mixture: plants shipped in from other regions of Australia, plus an informed selection of hybrids and exotics.
To restore indigenous species is to restore more than the "rhythms and diversity of the native landscape and a sense of the place".
It also saves our environment for future generations: Two recent scientific reports reveal that 40 per cent of the most damaging weeds have escaped from Australian gardens and that our obsession with exotic plants is creating diseases that can alter natural landscapes – forever. [For details > Plants >Weeds, on this website]
While training for my original career as an osteopath, students learned the basic rule: Do nothing that may harm the patient.
Applying the same rule to the environment, we ask the following questions:
- Is the plant an import, propagated overseas?
- Regardless of where it was propagated, does it compete successfully with indigenous species, for sunlight, nutrients and water?
- Has it established, or has it the potential to establish, self-propagating populations in native vegetation outside its natural range?
- Does it prevent or reduce the establishment of native species?
- Does it change geomorphological processes, fire regimes or hydrological cycles?
- Does it change the nutrient content of the soil?
- Does it confuse or interrupt the visual identity or continuity of the natural landscape?
Among the select minority of ornamental exotic trees that may deserve a place in the garden, one of our favourites is Magnolia grandiflora Southern Magnolia, a fire retardant, non-invasive and usually well behaved tree – given a moist, relatively fertile soil – from south-eastern USA. On account of its many desirable qualities, including its visual compatibility with much of Australia’s native vegetation, this beautiful tree, in our opinion, may be regarded as an ‘honorary native’.
Southern Magnolia has large glossy green leaves, and produces large, fragrant, cream-coloured flowers in summer. Reaching around 25 metres or more, it is best suited to parks and larger gardens. For smaller gardens, the dwarf cultivar Magnolia grandiflora ‘Little Gem’, that reaches only 7 or 8 metres, would be the better choice.
Gardenia augusta and its cultivars Gardenia augusta ‘Magnifica’, ‘Florida’ and ‘Radicans’ are among our favourite exotic shrubs. Gardenias all bear fragrant white flowers fading to cream. They are heavy feeders that need well-composted soil, warmth, sun, shelter, humidity, and a fair amount of water.
Waterlilies [Nymphaea species and cultivars] are surely among the most beautiful of water plants. Of the seven species indigenous to Australia, most have very large leaves, including Nymphaea gigantea Giant Waterlily, that produces blue flowers from late spring to late autumn. Indigenous to Queensland and northern New South Wales, Giant Waterlily is too large for most garden ponds and seldom survives further south than Coffs Harbour NSW, the southernmost limit of its natural distribution.
Nymphaea capensis Cape Waterlily, introduced from South Africa, is hardier, equally beautiful, has smaller leaves and similar flowers, and is often seen in lagoons around the mid north coast of New South Wales.
Our research indicates that Cape Waterlily and other exotic waterlilies have no adverse effects on the natural environment. For water features in the Sydney region that receive at least eight hours of sunlight a day, we unreservedly recommend them.
For advice on those most suitable for your water feature, consult one of the water garden specialists listed under Nurseries on this website. To achieve a natural appearance, two flower colours should be enough. [We planted blue and pink flowering waterlilies in our 120 x 80 metre lagoon, constructed in 2003.]
The above selection of exotic species is intended only as a guide. Gardeners with their own special favourites, need not hesitate to grow them, provided they present no threat to the environment and are closely monitored if necessary. [Tim Low, author of Feral Future, once told me that he grows Buddleia in his Brisbane garden: It brings the butterflies and reminds him of the garden of his childhood.]
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