A Tale of Two Iris

There are lots of iris in bloom right now in gardens.  Just on my way to work I have seen yellows and maroons, purples and blues.  Now I don’t know all that much about ornamental iris, but from what I can tell most are the bearded iris, of which there are literally thousands of cultivars to choose from. These are all of Eurasian origin – mostly German and Hungarian.   There are also Siberian and Japanese iris that are popular in gardens as well.  These are beardless iris, which look more similar to our native iris.  It isn’t always easy to figure out what iris you are looking at – there are close to 300 species of iris and endless cultivars and hybrids.

Iris versicolor is a great native for gardening

About 30 species of iris are native to North America, but there are only 3 species native to New York.  They are Iris prismatica, slender blue flag, found near coastal, brackish waters; Iris versicolor, northern blue flag, found in northeastern wetlands and along shorelines; and Iris virginica var. shrevei, southern blueflag, found in eastern wetlands and shorelines. Of these three, Iris versicolor, commonly called harlequin blue flag or northern blue flag, is our most common native iris in New York that I would love to see make its way into more gardens.  Considered native to much of the northeast, blue flag iris is absolutely stunning with its arching blue-green sword-like leaves and blue-violet blooms with veining and bright yellow on the sepals. Growing 2-3 ft tall with multiple blooms per stem, blue flag blooms in late May-early June.  Growing in full sun and hardy in zones 4-9, Blue flag iris is a great choice for gardens.

blue flags are very happy growing with common rush, sensitive fern, marsh marigold, and marsh fern at the edge of our nursery pond.

While normally found in wetlands and along shorelines, northern blue flag iris is quite adaptable in the garden, able to grow in regular garden soils.  It won’t spread as much as in wetter sites, but that is often just fine with the home gardener.  Northern blue flag iris is a great addition to rain gardens, shoreline buffers, and other native planting projects.  It is enjoyed by hummingbirds and native pollinators including mason bees and hover flies.

yellow iris along a lake shoreline in NY

Unfortunately, we have an invasive species that is taking over the habitat where we normally would find blue flag iris.  Iris pseudacorus, commonly known as yellow iris, yellow flag iris, or pale yellow iris, looks very similar, but is all yellow in color.  In fact, many people seem to think that they are the same plant – and just come in a yellow and a purple version.  This is not the case!  Yellow flag iris is native to Eurasia and was introduced to North America through the horticultural trade. It escaped cultivation and quickly spread throughout much of the country.  Banned or prohibited from sale in CT, MA, NH, and most recently VT earlier this year, iris pseudacorus is still commonly sold in NY nurseries.  There is also a variegated cultivar available for sale as well.

yellow flag iris have taken over this wetland

Yellow iris reproduces vegetatively and by seed. The seeds float and spread by water, allowing the iris to invade along waterways and throughout wetlands rapidly. It grows in dense stands, displacing native wetland plants and reducing habitat for waterfowl and fish.  It is able to tolerate salt, drought, and poor water quality, making it very competitive in disturbed wetland sites.

invasive yellow flag iris (pictured here) is different than the yellow bearded iris found in many gardens (which are not considered invasive)

The best time to identify yellow iris is when it is in bloom.  At other times of the year, it can be very hard to tell apart from native iris.  Blue flag iris doesn’t grow in huge stands like invasive yellow iris does. There are also slight differences in the capsules and stems/leaves, but unless you are an accomplished botanist, it is best to identify the plant when in bloom.   If you have identified yellow flag iris, and  you want to try to manage this invasive on your property, keep in mind that the rhizomes are poisonous, and can cause skin irritation for some people when touched, so wear gloves if you are going to try to dig yellow iris to remove it.  To be successful in removing it by digging, you have to get all the roots and rhizomes out, which can be pretty hard to do.  Or you can try repeated cutting if you have a small area. You will eventually wear it out.  At the very least, if the area is too big to dig or cut, cut off the seed pods before they mature so that more plants don’t pop up downstream.

© 2012, Emily DeBolt. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. If you are reading this at another site, please report that to us

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About Emily DeBolt

Emily has a Bachelors degree from Cornell University and a Master's of Environmental Interpretation from the State University of New York College of Environmental Science and Forestry. She lives with her husband Chris and Greater Swiss Mountain Dog McKinley in northeastern New York where they run Fiddlehead Creek, a 100% New York native plant nursery that specializes in growing plants for water quality and conservation projects.


  1. Donna@Gardens Eye View says:

    Emily I have planted our native blue flag in many wet areas of the garden including the pond. I have never seen the yellow iris, but will certainly keep an eye out for it…so many invasives are taking over wetlands here…hope this will not be one of them
    Donna@Gardens Eye View recently posted..Harmony Through Chaos

  2. UrsulaV says:

    There’s a really awesome cultivar of I. virginica var. shrevei called “Contraband Girl” that grows six feet tall. I don’t know why it’s not in more gardens—talk about drama!
    UrsulaV recently posted..My Mulch Brings All The Birds To The Yard

    • Carol Duke says:

      Thanks for the tip Ursula! Sounds fabulous!
      Carol Duke recently posted..Herbaceous Peonies Throughout the Gardens

  3. Emily DeBolt says:

    oh wow! that sounds lovely! do you have a picture?
    Emily DeBolt recently posted..Comment on January’s Plant of the Month by The Secret Lives of Dioecious Plants

  4. Carole Sevilla Brown says:

    We have so much Yellow Flag Iris around here people think it’s native. It’s in the parks, the wildlife refuges, along our creeks, everywhere :( And the nurseries still continue to sell it, which is a total bummer.
    Carole Sevilla Brown recently posted..Starting From Scratch In the Wildlife Garden

  5. Carol Duke says:

    Great info about identifying these invasive plants Emily. I did not know the rhizomes are poisonous.
    Carol Duke recently posted..Herbaceous Peonies Throughout the Gardens

    • Emily DeBolt says:

      yes – people that are into edible plants know this well. they look very similar to young cattails – which are quite tasty in fact. but you don’t want to confuse iris with cattail and eat the wrong one!
      Emily DeBolt recently posted..Comment on January’s Plant of the Month by The Secret Lives of Dioecious Plants



  1. Links – June 1, 2012 « Beautiful Flower Pictures Blog: Floral Photography by Patty Hankins says:

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