Yellow Flag Iris

Iris pseudacorus

Yellow flag-iris (Iris pseudacorus) is an eye-catching perennial that creates dense stands in wet areas, excluding native wetland species and threatening plant and animal diversity. Yellow flag-iris invades ditches, irrigation canals, marshes, stream and lake shorelines, and shallow ponds.  

Yellow flag iris is particularly bad for cattails, sedges and rushes that are used by many birds for nesting. Established infestations can reduce the carrying capacity of water storage in temperate wetlands, and can also block irrigation canals and flood control ditches—both of which are important for agriculture areas. 

Yellow flag-iris reproduces quickly through seed dispersal and horizontal root systems, creating thickets in the water like cattails. Up to several hundred flowering plants may be connected under the water, and fragments can form new plants when they break off and drift downstream. Yellow flag-iris is widely sold in nurseries and on the Internet for wet areas and well-mulched soil. While seeds disperse in the wind and water, popularity of the plant in the market exacerbate efforts to contain new infestations. 

Currently distributed in BC’s southern interior, yellow flag iris has quickly spread throughout the Okanagan valley, lower Similkameen valley, Christina Lake and other isolated sites in the West Kootenays. 

Plants are identifiable by showy yellow flowers with 3 sepals that curve backward and 3 petals pointing upwards. Leaves fold and clasp the stem at the base in a fan-like fashion. They stand erect or bent at the top, with long sword-like leaves toward the outside of the plant. At maturity, plants can reach 1.5 metres in height.

Warning: Yellow flag-iris can sicken livestock if ingested, though it is generally avoided by grazing animals. Contact with the resins can cause skin irritation in people.

A few native and ornamental alternatives to use other than planting yellow flag-iris include: Japanese Iris; Oregon Iris; Western Blue Iris; Butter and Sugar Iris; and Japanese Water Iris. Read more about these alternatives in the Grow Me Instead booklet for BC.