Yellow flag iris AKA Iris pseudacorus

Yellow flag iris is native to Europe, Western Asia and Northwest Africa.  It was brought to the United States, as an ornamental plant, during the second half of the 1800's. Soon after its introduction the plant began to escape cultivation.  It was a desirable ornamental loaded with cheery bright yellow flowers that that unfurl in late spring. It is also a very hardy plant with a tough fibrous almost woody rhizomatous root system. The plant spreads vigorously from the root as well as from the multitudes of disk-shaped seeds contained within its numerous seed pods.  In the right conditions, especially in a wet bog like setting, the plant can reach a height of four to five feet.  

When I first saw this plant on the Connecticut Invasive plant list, I was in denial.  I maintain an island of flowers along a roadside.  When I began planting the island with flowers some 20 years ago, I wanted to plant a variety of hardy perennial plants that I thought would be impervious to salt, sand, full sun, and capable of survival being watered solely by rainfall, rather harsh growing conditions.  This pretty flowering plant was already growing and thriving on my property, and it seemed to fit the bill, so it is one that I choose to plant in that garden.  Fortunately, perhaps due to the fact the irises are growing in an island surrounded by asphalt, they do not appear to have escaped.  I will mention here that it is not legal to sell this plant in Connecticut, however this plant is still available for purchase online.  There are many other options.  Do not add this plant to your landscape!

Yellow flag iris can often be found naturalized growing in wetland settings, along brooks and streams or in marshes.  In a brook setting you can easily imagine the numerous seeds and seed pods floating down stream where they eventually germinate and create more colonies. Colonies of this plant can alter the flow of water and cause flooding.  In addition, invasive non-native plants have the ability to crowd out native plants that wildlife depends upon to thrive.  In the case of yellow flag iris, the entire plant is poisonous as a food source for animals. Perhaps another reason it remains presently contained within my island of flowers. Soon I will be attempting its removal from that garden, though I will miss its bright sunny presence next spring. I am certain I can find other non-invasive irises to plant in its place. 

HOW TO REMOVE 

For small infestations hand digging with a good strong sharp shovel is best.  The fibrous roots need to be removed in their entirety to prevent regrowth.  Gloves are recommended for handling the roots as resin contained within them can cause skin irritation.  Do NOT use livestock to graze on this plant as it is poisonous for them as a food source.  

If the plant is growing in a pond, First remove and bag any seed pods, then cut the plants at their base below the water line.  Do not compost the seed pods!  That will just spread the plant!  Another method is to cover the colony with a PVC pond liner or heavy tarp being sure to eliminate any air pockets.  Extend the cover a foot beyond the colony.  Bury the edges of the covering and weigh it down securely. It is said that the PVC pond liner can inhibit gas exchange and kill the colony in as little as four to six months.  You will need to monitor the area afterward to be certain there is no post emergence.  

If the plant is growing on dry land, and you want to try an herbicide, a novel method for application on this plant is called wick wiping.  It involves securing a sponge with an elastic band to each end of a pair of kitchen tongs.  Since iris is a monocot like grass is, you need to select a non-specific herbicide that kills grasses as well as broad leaved plants.  Glyphosate is one that is recommended.  You then dip the sponges in the diluted herbicide and wipe the leaves with the sponges on the tongs.  This method cleverly prevents any overspray.

If there is a large colony growing in a wetland or pond setting, there are several water specific herbicides available that are said not to harm wildlife.  You will first need to check to see if a permit is required for their application.