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.
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.
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.
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 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.
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.
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