Christmas time is Agapanthus time. The lush heads of beautiful blue or white flowers brighten up many a garden. They're hard to overlook and have become a crowd favourite amongst hobby gardeners, but by hiding in plain site, we have been charmed into deception. In fact it could be argued that Agapanthus are Australia's most visible invasive weed.
Have a close look at bushland near urban areas and you will observe their slow invasion of the landscape. It is especially evident around this time of year as the flowers are in full bloom, smothering the natives ability to nutrient soils & sunlight.
A species becomes invasive when it distributes beyond the normal or acceptable limit, consequentially posing a threat to agricultural and ecological stability (DCCEEW 2022).
The problem lies within the growing capabilities of the root. As incredible as it is from an evolutionary standpoint, it is the same reason these plants are seemingly impossible to control. Technically, the Agapanthus roots are actually rhizomes. Originating from the Greek term "mass pf roots", rhizomes are essentially underground horizontal stems that allow the plant to spread and multiply inconspicuously before shooting up to the surface. These dense and clumping rhizomes will occupy any and all space available (fig.2). If left unattended they propagate incredibly quickly, displacing and killing off the surrounding flora in the process.
The Blue Mountains, to the west of Sydney, are a hotspot for Agapanthus and other alien plants. The qualities that make the Blue Mountains one of Sydney's iconic locations for both locals and visitors place them at particular risk of plant invasions (Hosking & NSW DPI 2005). "The Blue Mountains resembles the tip of a very large iceberg." It is one of the most at risk locations for weed invasion due to its urban accessibility and range of climates and soil types. "In the Blue Mountains, the ledges below the Three Sisters lookout are full of Agapanthus, which has taken over from whatever natives were there before," said Dr Hosking. "It may look pretty, but it is no longer a truly Australian landscape."
The risk is that an invasive plant can lurk in the background, unnoticed, for years, and then increase rapidly when conditions are just right: when the landscape is disturbed, the climate changes or its seed is carried by humans, birds, wind or water to a suitable spot. River valleys in places such as the Blue Mountains are particularly vulnerable, because seeds and plant fragments can be easily spread by water and find fertile ground to grow in. High levels of nutrients from sewage and land runoff are exacerbating the problem.
"The sandstone country is a harsh place for plants to live, but nevertheless alien plants from places like South Africa are now getting a firm foothold." Agapanthus is emerging as a potential weed threat in parts of NSW and Victoria because of its hardiness and drought resistance.
"Once it is established, you can't get rid of it," said Dr Hosking. "It likes fire, and herbicide is just too expensive. It is very aggressive and grows so densely it is capable of taking over native bushland. It is very hard to deal with."
One of the goals of the Weeds CRC and NSW DPI is to try and discover which plants are invading and where, so as to restrain the most dangerous ones before they become uncontrollable.
Even if a plant does little harm where it is first introduced, human activity and natural dispersal enable it to “explore” Australia in search of the perfect environment in which to multiply rapidly.
If you feel like doing your bit for the native bushland by clearing out some agapanthus, the best methods are to cut off the flower buds or heads before the seeds form, and dig out the plants with their roots. Herbicide is largely ineffective. If you can, try to prevent the seeds from getting into water courses.
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MORE INFO: (Dr John Hosking, Weeds CRC and NSW DPI, 02 6763 1129)
Species: Agapanthus praecox ssp orientalis Family: Alliaceae
Hardy perennial lily from South Africa, grows in thick clumps. Also called Lily of the Nile.
Leaves are thick, succulent, dark glossy green and strap-like, to 50cm long. There is a miniature or dwarf variety, also rather weedy.
Large, rounded heads of massed tubular flowers, blue or white, on a strong thick stem, to 1.2m tall, in summer.
Numerous small black shiny seeds are produced in a 5cm three-sided capsule, end of summer into autumn.
The underground structure forms large continually extending clumps, and seed may wash down waterways. This plant is also frequently dumped on bushland edges.
Impact on Bushland:
Spreads rapidly down drainage lines, but will also grow in dry areas. Dense clumping roots displace all other vegetation.
Throughout urban bushland, particularly the Blue Mountains.
Kangaroo Paw (Anigozanthos species) 50cm-2m; Spiny-headed Mat Rush (Lomandra longifolia) to 1m; Flax Lilies (Dianella species) to 60cm.
Cut the flower heads before the seeds form. Dig out clumps with a mattock. Try to get most of the roots. Does not respond well to herbicide.