Home About Us Our Services Publications Testing Submissions Contact Us Links

Day of the agapanthus (not triffids)

Christmas time is agapanthus time. The lush heads of beautiful blue or white flowers brighten up many a garden. We all recognize that they’re not natives—they hail from South Africa—but we have been seduced by their charms into ignoring their more insidious side.

Have a close look at bushland near urban areas and you’ll see that they are slowly invading, pushing aside the plants that belong there. Now is the time to look, while they’re in flower.

The Blue Mountains, to the west of Sydney, are a hotspot for agapanthus and other alien plants, which in places are starting to take over the landscape. The qualities that make the Blue Mountains one of Sydney's iconic beauty spots for both locals and visitors place them at particular risk of plant invasions, warned Dr John Hosking, of the Co-operative Research Centre (CRC) for Australian Weed Management and the NSW Department of Primary Industries, in 2005.

The more researchers look, the more plant invasions they are discovering. "In NSW alone in the past four years we have identified more than 120 alien plants that have either naturalized into the native environment or are in the process of doing so." The invaders include garden favourites like agapanthus, various Pittosporums (some of which are native), Juniperus, Cistus, Erica, Ajuga, Arbutus, Clematis, certain pines, cypresses and elms, and even native Australian plants from interstate, like WA kangaroo paws.

"The Blue Mountains resembles the tip of a very large iceberg. It is one of the most likely areas for new weeds taking off, because it is accessible, populated, has many visitors and [has] a range of climates and soil types. These together create many opportunities for invasive plants to establish.

"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.

"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.

Among other invaders of concern is Coolatai grass (Hyparrhenia hirta), originally introduced from South Africa in the 1920s to prevent erosion, and which has since taken off across large swathes of NSW, from the Northwest Slopes and Tablelands to coastal areas and the Blue Mountains.

"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.

Species: Agapanthus praecox ssp. orientalis  – Family: Alliaceae

Description

• 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 50 cm long. There is a miniature or dwarf form, also rather weedy.
• Large, rounded heads of massed tubular flowers, blue or white, on a strong thick stem, to 1.2 m tall, in summer.
• Numerous small, black shiny seeds are produced in a 5-cm, three-sided capsule, end of summer into autumn.
• Roots are fleshy, crowded, strong and tenacious.

Dispersal

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.

Distribution

Throughout urban bushland, particularly the Blue Mountains.

Alternative planting

Kangaroo paw (Anigozanthos species) 50 cm – 2 m; spiny-headed mat rush (Lomandra longifolia) to 1 m; flax lilies (Dianella species) to 60 cm.

Control

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.