Montbretia

Crocosmia x crocosmiiflora

Family: Iridaceae

Type of weed:

Flowering Months: , , ,

Description

A perennial hybrid herb.

The leaves are bright green and spear shaped.

Flowers are long, tubular spikes of orange, December to March.

Montbretia has annual leaves and flowers that die down in autumn after producing seeds and reappear in spring. Under the ground Montbretia has long strings of corms which break away when the parent plant is disturbed and begin to shoot. There may be 14 or more of these corms on each plant.

Don’t confuse with…

Montbretia can be confused with native Dianella spp, which frequently grow together. Native Gahnia spp and Stypandra spp can also look similar. The weed Watsonia looks similar but usually has a much broader leaf on a flatter corm.

Dispersal

It spreads vigorously through corm production. Corms are washed downstream. It is dispersed by the movement of soil containing corms; also by seed and in dumped garden waste.

Impact on bushland

Montbretia crowds out all other vegetation. The weight of the mass of corms can cause the collapse of stream banks leading to erosion and sedimentation. It thrives in soils contaminated by stormwater run-off. Montbretia is responsible for serious habitat loss.

Distribution

, . Particularly upper Mountains.

Alternative planting

Native plants

  • Native Water Ferns (Blechnum spp)
  • Native Saw-Sedges (Gahnia spp)
  • Dianella spp

Council provides a tool, on its Mountain Landscapes website, to help you choose native alternative plantings. Choose your village, soil, vegetation community and the purpose of your planting, and the tool will give you suggestions.

There are native nurseries in several Blue Mountains villages, including Glenbrook, Lawson and Katoomba. Please also ask at your favourite local nursery.

Control

  • For small young plants (less than 10 cm), digging up is successful if the soil is loose. As plants can have a long string of corms, digging up more established plants will only work if it is followed up repeatedly. Digging should not be used where the loose soil will erode, particularly on creek banks.
  • Wipe the leaves with a dilute herbicide mix where there are individual plants, small patches or where montbretia is found with native plants. This is an extremely successful technique when done correctly. The nine critical steps are explained simply in a PDF that you can download and print out: How to Make a Montbretia Weed Wiper. This download also contains instructions for use (with photos).
  • Dense patches of montbretia can be sprayed if away from all native plants and from any watercourses or swamps to ensure no risk of water contamination (surface or groundwater).

Herbicide: The techniques using herbicide need to be done when plants are actively growing (leaves are green). The best results are achieved if these are followed up after 6–8 weeks of application.

For more info

For key points on these techniques: