Yellow Flag Iris (Iris pseudacorus)

Perennial in the Iridaceae (iris) family. Grows up to 1.5m in height, with one or more showy yellow flowers per stem. Flowers are large, with three petals facing up, and three larger petals drooping down. After flowering, bunches of pods are formed that contain dark brown, buoyant seeds. Roots are 1-4cm thick and form mats.


Habitat and Ecology

Yellow flag iris grows in moist areas such as ditches and wetlands, spreading by rhizomes to form large colonies. It can grow in water up to 25cm deep, but tolerates drought. It prefers partial shade or full sun.


The large colonies out-compete native vegetation, and can alter watercourses. The plant is poisonous to humans and animals when eaten, and its sap can irritate the skin. Plants and seeds can clog irrigation systems, and the roots compact the soil.


Small populations should be dug up, taking care to remove all parts of the plant. Even small root fragments can grow a new plant. For large population, the flowers, leaves and seed heads can be cut off in July to reduce vigor and limit spread. All debris should be taken to a landfill, not put on a compost. Repeat the digging and cutting regularly. Report all sightings to LRISS.


BC Ministry of Environment and Invasive Plant Council of BC. 2011. Best Management Practices for Invasive Plants in Parks and Protected Areas of British Columbia.

District of Saanich. 2011. Yellow Flag Iris: Invasive Plant Alert.

Photo Reference: Nancy Loewenstein, Auburn University,