Some Plants That Roos Don't Like Very Much - Usually!
Kangaroos can be a real pest in Australian gardens, lovable as they are to some. They love roses. They also love many other plants including fruit trees and bedding plants. Bedding plants that aren't eaten can be squashed by their big feet. Even hardy native plants that may not appear at all attractive may be manna from heaven for kangaroos. There are few plants that kangaroos won't have a go at. In my garden they have plucked kalanchoes out of a pot and dropped them on the steps, not just once, but twice. Perhaps they are slow learners. Although aromatic and prickly plants may be left till last, they will be tackled in late summer when dry conditions have reduced the amount of green feed available. Butternut pumpkin are fair game during a dry summer according to my kangaroos.
There doesn't seem to be too many strategies that help. You can introduce barriers to protect precious plants and you can avoid planting shrubs and plants that are attractive to kangaroos. For the moment, that is about the sum total of 'how to keep 'roos out of the garden'.
A border of prickly plants such as Grevillea dielsiana or prickly moses (Acacia pulchella) will prevent access to soft-leaved perennials. However roos don't stick to paths and walkways and barriers need to be planted quite thickly if you are to deter all roos. They have no trouble hopping over a small hedge or pushing through if they think there is something nice on the other side.
Any stiff-leaved plants to 2 metres or more in height are helpful in preventing kangaroos from reaching the ornamental garden. Other excellent kangaroo-proof screens include densely planted pincushion hakea, large-leaved grevilleas and tall bottlebrushes. As a last resort you may need to consider a wall or metal railing. Many of my 'special' shrubs have rabbit-netting round them. If plants are particularly tasty, more open netting such as ringlock is not effective as the roos feed through the holes. I have a lovely potted topiary chrysanthemum because the roos trim every little bit that pokes through its netting protection.
Unattractive plants (to kangaroos)
It is believed that highly aromatic shrubs are not attractive to kangaroos. According to research conducted by the Curtin University of Technology kangaroos won't eat gum leaves or anything that grows near them because they don't like the smell.
Plantings of eucalypts, bottlebrush or paperbarks may be used to protect other plant species. A similar effect can be gained by using a mulch of shredded eucalyptus prunings. Aromatic plants such as boronias, native daphne and crowea are not usually eaten by kangaroos and seem to offer protection to surrounding plants. Lavender and rosemary have the same effect.
You may wish to provide alternative feed for kangaroos but this won't necessarily keep them from snacking on your plants. To keep them away from roses and fruit trees, provision or green areas or lawns may be helpful. Once branches get beyond their reach, a tree will usually survive. However a big kangaroo standing on a tripod of tail-tip and toe-tip can stretch a long way up and will pull down branches to feed on them. I have a hardenbergia (see photos below) which still gets trimmed around the bottom but it is so profuse now that the roos will not kill it.
As stated, kangaroos will eat nearly everything but there are a few things they don't like. Research has shown that red kangaroos avoid plants that contain quinine. For instance, they don't seem to like prickly or sharp-leaved plants such as the following natives: prickly moses (acacia pulchella), grevillea 'Boongala Spinebill' or 'Robyn Gordon', fuchsia grevillea (Grevillia bipinnatifida), melaleuca bracteata, devil's pins (Hovea pungens), hakea 'Burrendong Beauty', and snake bush (Hemiandra pungens). Other grevilleas which are left alone are Grevillea hookeriana, G.aquilfolia and G. curviloba.
Kangaroos rarely eat aromatic or fragrant plants such as red boronia (Boronia heterophylla), emu bush, crowea exalata, Swan River myrtle (Hypocalymma robustum), native mint bush (Prostantherea ovalifolia), native daphne (Philootheca myoporiodes) and Geraldton wax (Chamelaucium uncinatum).
While exotic plants may be especially tasty, kangaroos will avoid aromatic plants such as lavender, rosemary and wormwood.
They also don't like plants containing essential oils. Plants belonging to the Myrtaceae family produce essential oils which are toxic to bacteria in the gut of the kangaroo. Other marsupials, such as possums and koalas, are not affected by these essential oils. Indeed, the koala lives on a diet of gum leaves.
The Myrtaceae family includes such plants as the paperbark family (Melaleuca spp), gum trees (Eucalyptus spp), and bottlebrushes (Callistemon spp). If the kangaroo does eat these species, they lose their appetite and become sick, eventually dying of starvation. To test this theory, researchers fed western grey kangaroos with matched pairs of Myrtaceae species. Each pair has a plant with leaves containing essential oils and a plant of the same type bred in a nursery and lacking the essential oils. Not only did the 'roos avoid the plants containing essential oils, they also avoided (normally) favoured plants that grew near them. Although the tests were used only on the western grey species, researchers expect that similar results would be found with the eastern grey and the red kangaroo.
In 2001, bushfires wiped out many species in Whiteman Park, northeast of Perth, Western Australia. One plant that grew back in abundance, although it had not been see for some time, was the kangaroo paw which does not contain essential oils. Although relatively common, this plant was rarely seen in the park before the fire. After the fire, the kangaroos were selectively feeding on the kangaroo paw. Researchers decided that the 'roos had been keeping the roo paw eaten out. It is believed that the kangaroo's acute sense of smell helps it select its diet. Thanks to these findings, eucalyptus, bottlebrush and paperbark seedlings are now being planted near more delicate species to give them a better chance of survival. The seedlings will act as nurse plants to protect other plants around them. This information will help with the reafforestation of such areas as deserted mine-sites.