Yellow Iris – Oneida County Aquatic Invasive Species Program

Yellow iris is a showy perennial plant that can grow in a range of conditions from drier upland sites to wetlands, bogs, swamps, marshes, lakes, rivers, streams and ponds.  A native plant of Eurasia, it was introduced via the horticulture trade and can be an invasive garden escapee in Wisconsin’s natural environments. Other names for this plant include: Yellow flag iris, Water flag, European yellow iris, Pale-yellow iris.

This species is Restricted and may not be transferred (bought, sold, given away), transported, or introduced (imported or planted) in Wisconsin.

Oneida County Waterbodies with Yellow Iris:  Bass Lake, Crescent Lake, Kathan Lake, Katherine Lake, Kawaguesaga Lake, Lake Julia (near Rhinelander), Minocqua Lake, Muskellunge Lake, Rhinelander Flowage, Squirrel Lake, Sunset Lake, Sureshot Lake, Tomahawk Lake, and Tomahawk Thoroughfare. 

Do you think your lake has yellow iris? Contact us to schedule a visit to your lake for confirmation.

Identification:

• Flowers: Showy yellow flowers are between 3-4 inches wide.  Each flower has three sepals and three petals. Three upright petals are less showy than the larger three downward pointing sepals, which may have brown to purple colored streaks.  Yellow iris requires three years of growth before it can flower. Flowers bloom from April to June.
• Leaves & stems: Broad, sword-shaped leaves grow upright, tall and stiff. They are green with a slight blue-grey tint and are very difficult to distinguish from other ornamental or native iris species. Flowers are produced on a stem that can grow 3-4 feet tall amongst leaves that are usually as tall or taller.
• Fruits & seeds: Seeds are produced in fruits that are 6-angled capsules, 2-4 inches long. Each fruit may have over 100 seeds that start pale before turning dark brown. Each seed has a hard outer casing with a small air space underneath, which allows the seeds to float.
• Roots: Thick, fleshy pink-colored rhizomes spread extensively in good conditions, forming thick mats that can float on the surface of water.

Impact of Introduction: 

• This species has the ability to escape water gardens and ponds and grow in undisturbed and natural environments. It can grow in wetlands, forests, bogs, swamps, marshes, lakes, rivers, streams and ponds.
• It produces many seeds that can float from the parent plant and plants can spread vegetatively via rhizome fragments.
• Once established it forms dense stands with thick, submerged rhizome mats. 
• Yellow iris can out-compete and displace native species, which results in altered wildlife habitat and species diversity.
• Dense areas of this plant may alter hydrology by trapping sediment. This alteration reduces food supply and nesting habitat for fish and waterfowl.
• All parts of this plant are poisonous, which results in lowered wildlife food sources in areas where it dominates.
• Yellow iris can also cause skin irritation to humans and wildlife that come in contact with the plant.

​Control:

• Small populations may be successfully removed using physical methods. Care should be taken if hand-pulling plants as some people show skin sensitivity to plant sap and tissues. All parts of the plant should be dug out – particularly rhizomes and disposed of in landfill or by burning.
• Cutting the seed heads may help decrease the plant spreading.
• For additional control options, please refer to the DNR’s website at dnr.wi.gov/topic/invasives/fact/yellowflagiris.html