Blue Mountains dwellers will have noticed the appearance in spring of the bright fresh green spear-shaped leaves of Montbretia, Crocosmia x crocosmiiflora. In late summer and autumn these leaves are topped by long spikes of attractive orange tubular flowers.


Montbretia is a vigorous perennial hybrid bulbous plant from South Africa. It has annual leaves and flowers, dying down in autumn after producing its seeds, and reappearing in spring. It is a member of the plant family IRIDACEAE.


Under the Ground
Each Montbretia plant bears long strings of flattened corms which break away when the parent plant is disturbed, and begin to shoot. There may be up to 14 or more of these corms on each plant. As corms break off and and form new plants with corms of their own, the clump thickens and spreads.
 

An Adaptable Plant
Like many other weeds, Montbretia can tolerate a wide range of environmental conditions - it grows in any soil, wet or dry, poor or rich, in sun or shade. You will see it on roadsides, wasteland and the disturbed edges of bushland, but it thrives along creeklines and watercourses where it spreads with great vigour, fed by nutrients in the stormwater, and competes fiercely with all other plants, including other weeds.
 


New plants can be seen growing from the tip of each rhizome.

How Montbretia Spreads
In the Blue Mountains little viable seed is produced, but Montbretia reproduces vegetatively with great vigour. Each corm is a potential new plant, and will shoot when broken free from the parent plant. Corms live and produce plants for two years or more, and new corms are formed annually. Long rhizomes are also produced, each of which grows into a new plant.


Montbretia is also spread by the movement of soil which contains corms - during roadworks, for example. And unfortunately, far too many people have disposed of troublesome garden Montbretia by throwing it over the back fence or by dumping it on bushland edges - the main reason why it is so widespread today.


Many gardeners have 'got rid of' Montbretia
this way: by dumping it on bushland edges.
Areas like this are all too common.
 

A Threat to our Bushland
Montbretia competes fiercely, rapidly and successfully with native plants for root space in moist forest, swamps and along watercourses and waterfalls.

It completely dominates the ground layer, crowding out other plants and preventing the germination of any native seed in the soil. The weight of the mass of corms in the ground can cause the collapse of stream banks, erosion and sedimentation.
As stream banks collapse, the corms are washed down to infest new areas.



 


Montbretia threatens many of our most fragile bushland areas.

A Thoroughly Noxious Weed
The threat to the environment posed by Montbretia has been recognised by its declaration as a noxious weed under category W4c. This means that it may not be sold, propagated or knowingly distributed, and that an occupier must prevent its spread to an adjoining property. It can still be seen at fetes and in nurseries, and you will be doing our environment a great favour if you draw the seller's attention to its noxious status. And don't let anyone tell you it's all right because it's a sterile hybrid! As outlined above, Montbretia does not need seed to spread.

Montbretia is an invasive weed in all states and the ACT.


What Can I Do?
Anyone with some experience of Montbretia will know what a great survivor it is, and how hard it is to control this plant. Getting rid of Montbretia, or even preventing its spread, is certainly not easy. Where possible, dig deeply after rain to remove all the corms. In some situations the weed may form a mass of fine fibrous roots, and removal and replacement of all the soil may be the best option.

The weed responds poorly to herbicide spray, which does not translocate well to the corms. However, one local professional bush regenerator has had some success with Glyphosate sprayed during flowering at a ratio of 1:75. Or the foliage can be swiped over with full strength herbicide after flowering and before fruit set. Many inventive home applicators have been designed! Be sure to use impervious gloves and wash well afterwards. This could be tried in spring, when the plant is growing vigorously and has not yet formed its new annual corm.

Montbretia Weed Wiper banner
Tired of battling with Montbretia? Take a few minutes of your time and a few simple materials to make your own Montbretia wiper!
Download a PDF here.

How to Use your Montbretia Wiper will be coming soon.


Getting Rid of Montbretia
Whatever you do, don't put Montbretia in the compost! Disposal of the corms in the Otto bin is a safe option. Waste arriving at the tip is immediately crushed, compacted and covered with at least 15cm of soil, and the corms would soon be buried too deeply to make germination likely. Corms can be dried in the sun before putting them in the bin, and to speed up this process, they could be sealed in a black plastic garbage bag and 'cooked' in sunlight. Or try microwaving them!


Montbretia invading the Blue Mountains World Heritage National Park. Notice the stormwater outlet, bringing the weed all the nutrients and moisture it requires to dominate the ground level, exclude native plants, and prevent the germination of seeds.
 

Whatever method is employed, much follow-up work will be needed. Patience and persistence are required. Good luck with the removal! One thing is certain - if you wait until next year there will be much, much more to get rid of.

See this site's weed listing for Montbretia.

References
Blood, Kate Environmental Weeds A Field Guide for SE Australia, 2001
Muyt, Adam Bush Invaders of South-East Australia, 2001
 
Photos of corms and rhizomes Anne Bowman
Text and other photos Barbara Harley