Iris pseudacorus

Yellow flag iris

Family: Iridaceae

Origin: Eurasia, North Africa

Yellow Flag Iris growing on the side of a water body.
An iris that likes to have wet feet and is often found on the edges of streams and ponds. Seeds can be spread on the wind or by flowing water.
Photo credit: Peter Hamill, Marlborough District Council

Regional Pest Management Plan (RPMP) status

  • National Pest Plant Accord Species
  • Whole region — Sustained control

View more about the RPMP statuses

General description

Perennial rhizomatous herb < 1.5 m tall. Leaves are sword-shaped and arise in fan-like arrangement from base of plant. Flowers are yellow, < 12 cm in diameter and borne on erect stalks in September – December. Seed capsules are green and contain dark brown disk-shaped seeds.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell yellow flag iris. As yellow flag iris is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
  • You must not plant yellow flag iris within the Auckland region, unless you are transferring an existing plant on your land to another location within the boundaries of the same property.
  • You must destroy any yellow flag iris on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.


Wetlands, damp ground, pasture, shallow margins of still and slow-moving water bodies.


Seeds dispersed by wind and water. Vegetative spread from rhizomes, dispersed by water. Human-mediated dispersal through contamination of machinery and deliberate plantings.

Impact on environment

Forms dense mats, displacing vegetation. Accumulates sediment, altering stream flow and morphology. Impedes pasture drainage and is poisonous to livestock.


Site Management

Follow up treated areas 3 times per year.

Recommended approaches

Physical control

Method: Dig out.

Plant parts requiring disposal: Seeds and rhizomes.

Disposal options: Remove to greenwaste or landfill if practical.


Biocontrol is currently not available for this species.

Community agrichemical control recommendations

Certified Handler/Experienced agrichemical user: For terrestrial infestations:foliar spray spring to autumn 100ml glyphosate green per 10L of water and 20ml penetrant.

For aquatic infestations: foliar spray spring to autumn 100ml glyphosate green per 10L of water

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Single Yellow Flag Iris plant growingin grass.
Yellow flag iris has underground rhizomes that grow under the surface of the soil. New plants can grow from fragments of rhizomes that are moved to new areas.
Close up of Yellow Flag Iris flowers,
Yellow flag iris can form dense mats of rhizomes that don't allow native plants to grow. It can take over areas out-competing native plants.
Photo credit: Peter Hamill, Marlborough District Council