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Yellow Flag Iris

Invasive Description

Native to Eurasia and Africa, Yellow Flag Iris produces showy yellow flowers in the spring. Its bright green, sword-shaped, clumping foliage reaches up to 3 feet in height. It has been widely planted around the world as a showy garden or pond ornamental plant and has escaped cultivation.

Ecological Threat

Yellow Flag Iris is a large plant with strong competitive abilities. It forms dense colonies and impenetrable thickets in fresh or brackish water, displacing native species and altering habitat for animals. Its buoyant seeds spread long distances and can germinate even after an area burns. Rhizomes can survive prolonged droughts; small sections of rhizomes establish new plants. The iris has little wildlife value and is toxic to grazing animals. All parts of the plant are mildly poisonous.

How to Eradicate

For information on how to eradicate this invasive, view our statement on herbicide use and preferred alternatives for invasive plants.

Native Alternatives

You can replace this invasive plant with native alternatives. Here are some plants that make superior replacements.

Match your location on the Texas map to the color squares on the replacement plants below to find suitable replacements for your ecoregion.

Click for more details about the ecoregions
Additional Replacement Options: Blue Flag Iris (Iris virginica), Copper Iris (Iris fulva)

About the Region

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Salado, the location of our Fall 2025 Symposium, lies at the intersection of two ecoregions: the Edwards Plateau (Limestone Cut Plain) and Blackland Prairie (Northern Blackland Prairie).

The Edwards Plateau area is also called the Hill Country; however, this general term covers a much larger area extending farther north. Spring-fed creeks are found throughout the region; deep limestone canyons, rivers, and lakes (reservoirs) are common. Ashe juniper is perhaps the most common woody species found throughout the region. Additional woody species include various species of oak, with live oak (Quercus fusiformis) being the most common. Sycamores (Platanus occidentalis) and bald cypress (Taxodium distichum) border waterways. This area is well known for its spring wildflower displays, though they may be viewed in spring, late summer, and fall, as well. According to Texas Parks and Wildlife, average annual rainfall in the Edwards Plateau ranges from 15 to 34 inches.

The Blackland Prairie extends from the Red River south to San Antonio, bordered on the west by the Edwards Plateau and the Cross Timbers, and on the east by the Post Oak Savannah. Annual rainfall averages 30 to 40 inches, with higher averages to the east. This region is dominated by prairie species. The most common grass species include little bluestem (Schizachyrium scoparium) and Indian grass (Sorghastrum nutans) in the uplands and switchgrass (Panicum virgatum) in the riparian areas and drainages. Common herbaceous flowering plants include salvias, penstemons, and silphiums. This area has suffered greatly from overgrazing and agricultural use. Few intact areas remain, though many of the plants can be found along county roadsides throughout the region.

Our four host chapters (New Braunfels, Lindheimer, Guadalupe, and the Hill Country chapters) are located in one or both of the ecoregions above. However, the eastern portion of Guadalupe County also falls within the Post Oak Savanna ecoregion. Annual rainfall averages 35 to 45 inches, with higher averages to the east. A wide variety of hardwood trees are found, including several species of oaks, elms, and in the Bastrop area, loblolly pine (Pinus taeda). Grasses and forbs dominate in the open savannas, with most common grass being little bluestem. Ranching, agriculture, and fire suppression have allowed woody species to encroach on the once-open savannas.

Source: Wildflowers of Texas by Michael Eason