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Yellow Flag Iris

Species
Iris pseudacorus

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

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