Bulbs and corms that should be avoided
The following bulbs and corms are some of the most invasive species that are still readily available, either commercially or privately. In many cases, the factor that may help gardeners decide whether or not to grow a particular plant will be the proximity of their home to bush or farmland.
Babiana or baboon-flower
Corms of Babiana (Babiana stricta and B. disticha) species are reproduced annually. In addition to these offsets, babianas also seed prolifically. B. stricta is a serious weed in the Darling Range, Avon Valley and the Swan Coastal Plain, where it has invaded clay-based woodlands and wetlands from Gingin southwards — it also occurs at Albany.
Flowers range in colour from white through lilac and pinkish-mauve to deep violet. B disticha is recognisable by its irregularly shaped lilac or mauve-blue flowers, with two petals having distinctive white markings. Preferring sandy soil, this species has invaded urban bushland and disturbed land from Perth to Busselton.
Black flag
Black flag (Ferraria crispa) is sold by some mail order companies and casual sales outlets. Its popularity is surprising, given the unpleasant odour of the black mottled flowers. Outside the flowering season, black flag can be recognised by its unusual succulent-looking bracts and leaves.
Its reproductive capacity makes it an insidious invader that can form mono-cultures. Black flag will seed prolifically, but more sinister is its unusual system of stacked corms, of which only the most recent are susceptible to herbicides. Corms lower in the column remain untouched by chemicals, and have the ability to sprout new corms.
Chincherinchee
All Ornithogalum species are highly invasive and contain toxins, but chincherinchee (Ornithogalum thyrsoides) is the most notorious because it can poison livestock.
Gardeners intending to plant chincherinchee, or those already growing it, should consider their location. Farmers, and anyone living in a regional town or in suburbs alongside hobby farms, national parks, or urban reserves, should not acquire it, and should attempt to eradicate existing plants from their gardens. However, inner-city dwellers living away from sensitive environments can grow these bulbs fairly safely.
Freesia
There are many freesia cultivars, but the Freesia alba x leichtlinii hybrid is the one that has established itself densely in natural habitats, where it spreads by seed, offsets, and cormels on the stems. Flowers vary from white through cream to light yellow, sometimes with purple tinges.
Freesia is loved for its perfume, so its corms are a favourite subject of exchange between well-meaning gardeners who have no idea of its capacity to escape. Freesia is a serious weed of urban bushland, coastal heath, and woodland and granite areas from Gingin to Israelite Bay.
Hesperantha
Hesperantha falcata is reproduced by an annually renewed corm. The white flowers, which are purplish-brown on the outside of the petals, open in the late afternoon. Generally only one or two flowers on the spike are open at any one time, which makes the ornamental value of Hesperantha fairly low.
It is a common weed of wetlands and damp grassland on the Swan Coastal Plain and in the Darling Range. In these areas it may be very abundant, although usually it does not dominate other vegetation.