Android app on Google Play Available on the App Store Invasive Species Council of British Columbia logo

Ask us

We'd love to hear from you. If you have any questions or concerns, let us know!

learn more

Donate Today

Your donations will help support healthy communities in BC! Join a growing community of supporters who care

learn more

Get Involved

Find out what you can do to make a measurable difference in your community

learn more

Become a Member

Enjoy the opportunity to network with others who take an active interest in invasive species management in BC. Join us today!

learn more

Commit to be PlantWise

Help to reducing the damage created by invasive species in British Columbia. Climb on board with the ISCBC and commit to becoming PlantWise!

learn more

Yellow Flag Iris

Introduced from Eurasia, yellow flag iris is a beautiful, exceptionally fast-growing species with sword-shaped leaves and showy yellow flowers. Yellow flag is a popular choice for water gardens, but is now recognized as an extremely aggressive invasive.

How does it spread?
Yellow flag iris spreads both by seed and from broken rhizome fragments that are carried by water currents, wind, wildlife and humans. 

Where would I find it?
Yellow flag Iris thrives in temperate wet grasslands and pastures, ditches, irrigation canals, fens, freshwater wetlands, salt marshes, streams and lake shorelines, shallow ponds and lakeside mudflats. It prefers silty or rocky fertile soil and can tolerate water to depths of 25 cm, highly acidic soil (pH 3.6 – pH 7.7) and full sun to partial shade exposure. It has fouled extensive habitat throughout southern BC and is currently spreading in the Southern Interior.

What problems does it cause?
In shallow water and alongside waterways, yellow flag forms dense thickets of foliage to 2 m or more tall. In water, the thick root mats collect sediment and reduce flow, displacing native plants and damaging wildlife habitat. All parts of yellow flag iris contain poisonous plant resins that can cause a variety of human skin irritations, as well as illness in horses and other grazing animals. Eradication is difficult, as seed is plentiful where yellow flag is established and even tiny rhizome pieces re-grow.

Additional Recommendations

  • Cattails (Typha latifolia) BC native (z3)
  • Bearded Iris Yellow Cultivars (Iris germanica) (z3)
  • Blue Flag Iris (Iris virginicum) (z5)
  • Marsh Marigold (Caltha palustris) BC native (z2)

A provincial initiative coordinated by ISCBC


Gardeners: Commit to be PlantWise
Help Spread the Word: Become a PlantWise Ambassador
Industry: Become a PlantWise Industry Partner
Report Invasive Plants

Get Involved


Let Plantwise Industry Partners help you choose and purchase only non-invasive plants to suit your needs. Find one near you!

View Partners Become an Industry Partner