10 plants you'll regret adding to your Australian garden

These plants have been marketed so successfully as great options for gardens, they're widely recognised and planted across homes from coast to coast in Australia. Many are undeniably beautiful or structurally interesting.

What the nursery tags don't mention is that some of these plants can lift the foundations of a house, smell like rancid butter or have thorns that can lodge deep into the skin. Many of these issues don't arrive until far down the track, when the plant is well established and much harder to manage.

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1. Bougainvillea (Bougainvillea spectabilis)

Bougainvillea thorns evolved as a mechanism for scrambling through dense Brazilian rainforest understorey, hooking onto other plants for support. They are long, rigid, sharply curved and barbed and can go through standard gardening gloves and break off in skin. Pruning bougainvillea, which it needs regularly to flower well, is a genuinely unpleasant job even with thorn-proof gloves and long sleeves.

Its vigour comes from its native habitat of periodic drought and high light intensity, conditions that much of Australia replicates well. In warm climates it grows several metres per season and in Queensland and northern WA it self-seeds and is listed as a weed in riparian areas. Bougainvillea in a large pot, kept root-bound, is an easier proposition.

2. Running bamboo (Phyllostachys)

The rhizomes of running bamboo travel laterally underground in every direction simultaneously at a rate of a few metres per year in good conditions. After just a few seasons they can find their way under paths and fences, beyond property lines and under foundations. Root barriers can be installed to a depth of at least a metre and checked annually for gaps, but it's far from a fool proof solution.

In its native Chinese forest habitat the running rhizome habit evolved to colonise clearings rapidly after disturbance. Competing root systems in the forest slow it down, but there is no plant to do the same job in a suburban garden. Removal of established running bamboo from a garden bed can be a never-ending and gruelling task. If you want the look, choose a clumping variety which doesn't have the same explosive growth habit.

3. Mirror bush (Coprosma repens)

Mirror bush is salt tolerant, fast-growing, dense and glossy. The problem is that it also seeds prolifically. The fleshy berries evolved to be eaten and distributed by the native pigeons and warblers of its home range in New Zealand and Lord Howe Island. Australian birds are just as efficient at the job. It's a significant environmental weed in coastal NSW, Victoria and Queensland.

The self-seeded plants that turn up in your beds, along your fences and in path gaps need to be removed manually and repeatedly. For gardeners near remnant bushland, the plants establishing beyond your boundary could become your responsibility. For a coastal hedge that behaves, westringia, coastal banksia or native coastal rosemary are worth considering instead.

4. Ornamental pear (Pyrus calleryana)

Ornamental pear is extremely popular as it's fast-growing, has a neat upright form, white spring blossom and beautiful autumn colour. However, the spring blossom smells like rotting fish (or something else unprintable) and is detectable from several metres away. The smell comes from trimethylamine that evolved to attract flies and beetles as pollinators.

The most common cultivar, 'Bradford', has narrow branch angles that become inherently weak as the tree matures. After fifteen to twenty years the branches can split. Many Australian councils are now removing ornamental pears from streetscapes for exactly this reason. For the full picture on invasiveness and ecological impact, see our guide to plants to avoid in your Australian garden.

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5. Wisteria (Wisteria sinensis)

Years one and two of wisteria offer a well-behaved climber with cascading purple flowers. By year five the woody stems are thickening noticeably. By ten years, they're in your gutters, under roof tiles, wrapped around structures and starting to strangle nearby trees. Wisteria finds every gap and every crack and can pull decking away from houses.

In its native Chinese and Japanese forest habitat, wisteria has centuries-old trees to compete with, natural herbivores and fungal pathogens that limit its growth. In an Australian garden pergola it has none of those constraints. It also requires hard pruning twice a year to flower well and stay manageable. For a fragrant climber that won't eat your house, hardenbergia, pandorea and billardiera offer flowers and coverage.

6. Ginkgo (Ginkgo biloba)

Ginkgo trees are either male or female but you can't determine the sex until the tree matures and begins to fruit. The female trees produce fruit that smells intensely of human vomit. The smell comes from butyric acid in the fleshy seed coat which is the same compound in rancid butter. It evolved to attract large mammals that would eat and disperse the seeds. The mammals it co-evolved with are mostly extinct.

A mature female ginkgo dropping seeds onto a path in autumn makes outdoor areas genuinely unusable for weeks. The seeds are also mildly toxic and slippery underfoot when decomposing. Many specialist nurseries now sell grafted male clones that don't fruit so ask specifically for a male cultivar like 'Fastigiata' or 'Princeton Sentry' and confirm it won't fruit before you buy.

7. Pampas grass (Cortaderia selloana)

Pampas grass looks spectacular when young and requires almost no care in its first few years. Down the track, the leaves have razor-sharp serrated edges that cut skin on contact, the plumes produce thousands of wind-dispersed seeds per season, and the plant is a declared noxious weed in Victoria, NSW, Queensland, South Australia and Western Australia.

The razor-sharp edges evolved as a defence against large grazing mammals on the South American pampas like guanacos, rheas and others. On the pampas it also has natural fungal pathogens, competing grasses and seasonal fire to regulate its spread. Cutting it back requires long sleeves, heavy gloves and eye protection. The root system resists manual removal and chemical control requires repeated applications. For a similar arching grass form, native grasses including Austrostipa and Rytidosperma are worth considering instead.

8. Liquidambar (Liquidambar styraciflua)

The autumn colour of liquidambar is beautiful. The issue is the seed balls, which are produced on a single tree by the hundreds. They are spiky and woody and fall across lawns, paths and outdoor areas from autumn through winter. The capsules evolved to catch in the fur of large mammals for dispersal and the aggressive surface roots are an adaptation to the seasonal flooding and drought of its native river valley habitat in the eastern United States.

Both strategies continue in your garden regardless of whether they are useful to you. By the time the root problem is obvious the tree is large enough that removal is expensive and difficult. Brachychiton acerifolius (Illawarra flame tree) offers equally spectacular deciduous colour and is genuinely native to NSW and Queensland.

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Before you plant anything

The plants on this list share a common characteristic: the consequences arrive years after the purchase decision, when removal has become expensive and difficult. The question worth asking before you buy anything large, fast-growing or vigorous is not "what will this look like?" but "what will this do to my garden in ten years, and how will I manage it?"

9. Arum lily (Zantedeschia aethiopica)

The large white spathes of Arum lily are genuinely beautiful and it's widely sold at mainstream nurseries nationally. However, all parts are toxic to humans, dogs and cats. The calcium oxalate crystals cause intense burning and swelling of the mouth and throat and it's a declared weed in Western Australia where it colonises bushland and waterways aggressively.

The rhizome fragmentation habit evolved as a response to seasonal flooding and soil disturbance in its native South African wetlands. This is its way to recolonise disturbed ground rapidly from fragments. In a garden bed it responds to every dig with exactly the same strategy, which means digging a clump out almost guarantees it reshoots. For a similar lush foliage effect without the toxicity, native gingers, dianella and native iris are worth considering instead.

10. Agave (Agave americana)

Each leaf of agave terminates in a rigid spine hard enough to penetrate skin to the bone. It has been recorded to also cause serious eye injuries. In a pot on a terrace, away from paths and people, agave can be managed. At path edges, near play areas or in mixed beds where you need to reach past it, it's a persistent hazard.

The terminal spine and marginal teeth evolved to deter large herbivores in Mexican desert scrub. The monocarpic habit (flowering once then dying) is an evolutionary strategy to concentrate energy into a single seed dispersal event. The sap irritates skin and the spines stay dangerous after the plant is dead. For a bold, structural, low-water alternative, xanthorrhoea (grass trees) and large-form dianella offer genuine architectural presence.

What these plants have in common

What these plants share is a gap between the purchase promise and the lived reality, and that gap tends to widen with time. The consequences arrive years after the decision and are difficult or impossible to reverse.

For plants that cause problems for different reasons — invasiveness, ecological impact, and the harm they do beyond your garden boundary — see our guide to plants to avoid in your Australian garden.

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