When our native shoreline ecosystems thrive, our lake thrives. Invasive plants pose a significant threat to the environment and can have negative consequences for us as well. The invasive plant yellow flag iris, though beautiful, is a blooming bully. We are working hard to protect Lake Leelanau from the invasive plants that grow in its depths, but we need you to join us in our fight against the invasives on your shorelines and preserve our natural heritage. Read on to learn how to identify and remove yellow flag iris from your property.
Meet Yellow Flag Iris
The danger of the perennial yellow flag iris is that it is pretty and a horticultural favorite. The bright yellow flower on the sword-like leaf is beautiful in large clumps. According to the US Geological Survey, this Eurasian-native plant arrived in North America in 1871, got to Michigan in 1937, and was first spotted in northern Michigan in 1954. It probably “escaped” from gardens early and now is a thriving invasive.
Yellow flag iris blooms from May to early July and prefers wet areas along shores, roads, and mud. It is easy to identify because it is the only primarily yellow iris (the blue flag iris that blooms later is native). This plant grows between 1 ½ to 3 feet tall, spreading by its abundant seed production and vigorous rhizome growth.
The Problem
As the root mass gets bigger, the plant creates a monoculture, hedging out other native species. The fairly large seeds (~1/4”) will drop into the water, float away, and be washed up on shore to begin a new plant. The seeds germinate quite easily, allowing for its rapid spread. Once established, yellow flag iris can outcompete native cattails, sedges, and rushes, reducing habitat for birds, fish, and amphibian species. The aggressive growth of rhizomes can have many negative impacts on the structure of shoreline and wetland environments. Dense stands of yellow flag iris compact soils and increase sedimentation by slowing watercourses, further favoring colonization by the species. The roots are poisonous to animals, and all parts of the yellow flag iris plant are poisonous to humans. The plant material contains resins that can cause skin irritation and blistering.
Yellow Flag Iris on Lake Leelanau's Shoreline
In 2024, a shoreline survey was completed to identify all the yellow flag iris along Lake Leelanau’s shoreline. The yellow dots on the map above indicate all properties at which yellow flag iris was identified, ranging from an individual plant to multiple large plants along the shoreline.
In our attempt to control yellow flag iris, we are contacting all of the property owners to educate them on their options for control. If you have yellow flag iris on your property, please read on to learn how you can be a part of the solution for protecting Lake Leelanau from this beautiful but dangerous invasive plant.
How to Control The Spread
Control of yellow flag iris can be difficult, but we have put together some guidelines to help you. Together, we can make a difference.
If you have just a few plants in an accessible location:
Dig and Dispose. Dig the plants up, ensuring complete removal of the rhizome system. The removal of the rhizome, or the connecting underground roots, is necessary since any bit of the rhizome left behind can propagate new stems. Other issues that may hinder hand removal efforts include accidental dispersal by dislodging seeds that float away, water turbidity, transportation of removed plants off site for disposal, and accidental removal of any dormant native tubers, bulbs, and seeds in the soil bank. Plants should be bagged and disposed of in the garbage can. Please remember that protective clothing should be worn while removing yellow flag iris, as it will cause skin irritation. Until you can dig up the plant, remove the flowers immediately after blooming to prevent seed maturation and spreading.
Follow-up monitoring and maintenance are essential if hand removal is the chosen control option.
The yellow flag iris is poisonous to humans. Its resins can cause skin irritation and blistering. Wear protective clothing when removing this plant.
If there are too many plants to dig and they are in a dry area:
Use benthic barriers. Cut the plant to the ground and stake down an 18-ounce or 7mm vinyl mat covering beyond the edge of the plants by at least 8 inches. Ensure the roots don’t escape beyond the edges by slipping the edges of the mat into the soil using a shovel or spade. Use wooden stakes and/or heavy objects (rocks, bricks) to keep it secure. Keep in place for a single growing season (spring to winter) or up to a full year. Or,
Use herbicide. Only apply on a windless day when there is no rain in the close forecast. It is most effective for yellow flag iris in September. To reduce the spread earlier in the year before applying herbicide, before the plant produces seeds, cut the flower head into a plastic bag and dispose of it in the trash. If you have a mix of yellow flag iris and blue flag iris (native) on your shoreline, mark the yellow flag iris during its bloom time so you know which ones to treat later.
If there are too many plants to dig and they are in a wet area (at least 5cm year-round):
Keep cut. Continuously cut off the foliage at ground level. Repeated cutting at ground level will result in plant death within 1 year.
Regardless of the control option, please continue to monitor the area. If you have any questions, contact us at [email protected].
Conclusion
While controlling invasive species can feel like an uphill battle, remember that even small-scale efforts contribute to a larger movement. By staying informed, taking consistent action, and collaborating with your neighbors, you can make a significant difference. Together, we can protect our native ecosystems and ensure a healthier lake for future generations.
Yellow Flag Iris Resources
Blog photos from top to bottom from St. Louis River Alliance, Jon Richfield via Wikimedia Commons, University of Minnesota