INVASIVE OF THE MONTH - YELLOW FLAG IRIS

Yellow flag iris (Iris pseudacorus) is a showy perennial plant native to Eurasia.

It was introduced to the United States as an ornamental plant in the early 1800s.

Its striking yellow flowers and hardy nature made it popular for decorative ponds, rain gardens, and landscaping along shorelines. Additionally, it was sometimes planted for erosion control due to its robust root system.

Unfortunately, its highly adaptable nature, aggressive growth, and ability to spread via rhizomes and floating seed pods have allowed it to escape into our native landscapes. Over time, it spread into natural waterways, wetlands, and lakeshores, where it now poses a serious ecological threat.

Adding to its impact, all parts of the plant are poisonous, limiting food sources for wildlife in areas where it dominates.

This species can thrive in a variety of environments, including wetlands, forests, bogs, swamps, marshes, lakes, streams, and ponds — both in controlled landscapes and natural settings.

Infestations can also alter water flow and drainage patterns by trapping sediment, which can raise water levels, slow currents, and disrupt the natural balance of aquatic ecosystems.

Today, yellow flag iris is considered highly invasive in many parts of the U.S., including Wisconsin, where it is replacing native plants and disrupting shoreline ecosystems.

Efforts to control it focus on preventing its sale, educating property owners, and encouraging native plant alternatives (like the native purple flag iris).

This plant is classified as RESTRICTED by Wisconsin DNR - READ here

HOW TO ORGANICALLY REMOVE YELLOW FLAG IRIS

To organically remove yellow flag iris, focus on manual removal by digging up the entire plant, including rhizomes, and repeated mowing or cutting to deplete energy reserves, along with vigilant monitoring for regrowth.

Here's a more detailed breakdown of organic control methods:

Manual Removal:

Digging

Carefully dig up the entire plant, including the rhizomes, which are the

underground stems that allow the plant to spread.

Timing:

Digging is most effective before the plant goes to seed, and you should repeat

this process to prevent regrowth. ALWAYS REMOVE flowers and SEEDHEADS before

they are released into the environment.

Protect yourself

Be mindful that the plant's sap can cause skin irritation, so wear gloves and long

sleeves.

Disposal:

Properly dispose of the removed plants to prevent further spread, such as bagging

them and placing them in the trash.

Mechanical Control:

Mowing/Cutting: Repeatedly mow or cut the plant and flowers, especially before it sets seed. This will deplete the plant's energy stored in the rhizomes, eventually weakening and killing it. Again! ALWAYS REMOVE flowers and SEEDHEADS before they are released into the environment. This method requires consistent effort over several years.
Cover / tarping: For larger patches, and if possible, cover the plants with a thick, light-impermeable black tarp to prevent sunlight. Ensure the tarps extend well beyond the edges of the patch to prevent regrowth. This will take several months to a year.
Water Level: If the plants are in standing water, continual cutting of all leaves and stems below the waterline can be effective.

Monitoring

Regularly monitor the area for regrowth and address any new sprouts promptly.

Prevention

Consider introducing native flowering species to the area to replace yellow flag iris.

Blue Flag Iris (Iris versicolor) -known for its striking blue-violet flowers with delicate yellow and white markings. It is a low maintenance plant that blooms in late spring to early summer. It not only adds vibrant color to landscapes but also supports pollinators like bees and butterflies.
Swamp Milkweed (Asclepias incarnata) – Pink flower clusters attract pollinators and support monarch butterflies.
Joe-Pye Weed (Eutrochium spp.) – Tall plants with large pinkish-purple flower heads ideal for wet areas. This plant is a pollinator powerhouse, rich with nectar and has deep roots that stabilize the soil.
Cardinal Flower (Lobelia cardinalis) – Vibrant red flowers that attract hummingbirds.
Great Blue Lobelia (Lobelia siphilitica) – Striking blue flowers that thrive in damp soils. Highly attractive to native bees, butterflies, and hummingbirds, providing an important late-season nectar source.

Here are other alternative ideas from Wisconsin DNR

Also, native grasses and sedges are excellent for erosion control and provide habitat and protection for birds, amphibians, and small mammals.

Fox Sedge (Carex vulpinoidea) – Dense clumps that stabilize soil along shorelines.
Lake Sedge (Carex lacustris) – Thrives in wetlands and offers excellent erosion protection.
Prairie Cordgrass (Spartina pectinata) – Tall, deep-rooted grass that stabilizes banks.

University of Stevens Point

"Manual removal of yellow iris is difficult because of its strong rhizome network. Removal of small clumps is easier in areas of soft, water-logged substrates, and these clumps should be grasped as far down the stem as possible and pulled straight up to have the best chance of removing the entire rhizome. Digging is also an option—care should be taken to get underneath the entire rhizome without breaking it, and removal of native species must be minimized. All plant material must be removed from the site and disposed of away from water bodies. Yellow iris can cause skin irritation, so gloves should be worn when working with this species.

Protecting our shorelines from invasive species like yellow flag iris is essential for preserving the health and beauty of our lakes.

By removing this aggressive plant and replacing it with native species, we can restore vital habitats, improve water quality, and support wildlife.

Your efforts — big or small — make a lasting difference. Together, we can ensure our lakes and rivers remain vibrant and healthy for generations to come.

Invasive species- Natures Conservancy video - watch HERE

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