Yellow iris: invasive, increasing, and in bloom right now along the St. Croix River

Help control the spread of this non-native plant which hurts wildlife habitat and crowds out native species.

May 31, 2018

2 minute read

Yellow iris (Photo by J Hokkanen via Wikimedia)

Yellow iris is an invasive flower that is increasing its presence along our waterways. The plants are native to Europe, Western Asia, North Africa, and the Mediterranean region. They were brought to the United States for use in gardens, for erosion control, and to remove metals from sewage treatment plants. Today, they are found across the northern U.S. and Canada.

Yellow iris spreads quickly through rhizome and seed reproduction, and tends to crowd out native plant species (like blue flag iris) and decrease plant and animal diversity. The yellow iris is unpalatable to wildlife, and can cause skin irritation in humans if handled without gloves.

During the months of May and June, the plants are easily identified by their yellow flowers. They have long, narrow, sword-shaped leaves, and typically stand between three and four feet tall. When not in bloom, yellow iris can be confused with native blue flag iris, which has blue-purple flowers. Along the St. Croix River, yellow iris are found from north of St. Croix Falls to Marine on St. Croix, as well as along the headwaters and Upper St. Croix Lake in Solon Springs, WI.

To help limit the spread of the plant, cut the flowers off and dispose of them to prevent the seeds from developing and spreading. To learn more about invasive species and their impacts to Wisconsin’s waters and economy, visit http://dnr.wi.gov/lakes/.