What’s that? A non-indigenous aquatic species

Submitted to Dorchester Banner/Laetitia Sands
Yellow flag iris, imported as an ornamental when the U.S.A. was in its infancy, is striking, but a plant to avoid at all costs.

No, it’s not swimming, but it sure is on the move.
I’ve recently heard interviewers ask experts, particularly with regard to the Covid-19 pandemic: “What keeps you awake at night?” or, “What do you worry about at 3:00 o’clock in the morning?” The question could well apply to gardening, too, and asked of any gardener. What would you answer?
My answer, in a word: Invasives. In the past, I’ve tangled (and still do) with invasives like phragmites reeds, Japanese honeysuckle and silver poplar trees. But now there’s a new enemy gobbling up space in my yard. If you have it in yours, or contemplate planting it, read this cautionary tale and take action before it’s too late.
The other day, I lay awake from 3:00 to 4:00 A.M., wondering how on earth I was going to tackle the invader without resorting to expensive professional help, and I don’t mean a sleep therapist.
A few years ago, a friend asked if I would like some yellow flag irises she was thinning out in her garden. They’d grown tremendously and she’d had a hard time unearthing the ones she didn’t want, my friend said. ”Sure, I’ll take some!” I answered enthusiastically.
I planted them along the edge of my property, where a slight ditch separating my lawn from the neighbors’ tended to accumulate water, which I thought the irises would like. For a few years, the clump seemed to do little and produced no flowers, much to my disappointment. Last year, it presented me with one or two not very sweet smelling, yellow flowers and a lot of tall, spear-like green foliage.
This year, I got five or six flowers, but I noticed the clump had taken off. It measured 15 to 20 feet around and some of the spears stood six feet tall. A little further along, a second, smaller clump had appeared and about 15 feet along from that, a third one had popped up.
It occurred to me their presence might explain why a highbush cranberry shrub – a lovely large bush with striking white flowers, which stands beside the irises – had been ailing for the past year. Ditto an elderberry patch.
Some plants have an unpleasant ability to inject a substance into the surrounding soil which makes the ground toxic to certain other plants. This is called allelopathy. Black walnut trees do it, for example.
Searching around online, I discovered a website called WAG — Ask a Vet, which said all parts of yellow flag irises were poisonous. The roots and leaves closest to the soil (and easiest found by wildlife) were the most toxic, the site said.
A mild to moderate case of poisoning by the plant could cause diarrhea, drooling and lethargy in horses and other livestock. Usually, animals recovered in 24 to 48 hours, but a severe case could lead to tremors, convulsions, confusion and even sudden death.
The vets warned that shipments of hay to feed livestock sometimes contain stems and flowers of yellow flag irises, which caused “widespread gastroenteritis” (tummy upsets). For those readers who have hay-eating animals, they advised: “carefully grow and manage your own hay” or “stick with one supplier.”
Maryland made it illegal to buy, sell, transport or transfer iris pseudacorus, as the yellow flag is known botanically, in 2017. (My clump came from my friend before that, but I should have connected the dots later).
The Maryland Invasive Species Council flagged the plant, which also goes by the name of water iris and yellow iris, because of its “invasive tendencies and negative impacts in natural and agricultural systems.”
In the rogues’ gallery of invasives, Maryland ranked it among the worst of the bad – in the “Tier 1” high risk category, alongside plants like fig buttercup and shining cranesbill.
Alarmingly, yellow flag can easily be mistaken for the native blue flag iris (iris versicolor). It’s only at this time of year, when the plant flowers, that you can easily tell them apart. Yellow flag is the only completely yellow iris that grows in the wild.
Another, less obvious, way to identify it is by the seed capsule. Yellow flag has a six-sided, oblong capsule(containing around 120 seeds), the blue iris has a three-sided seed pod.
Yellow flag spreads not only by seed, but by 1-1/2 inch thick, fleshy rhizomes that grow vertically, four to eight inches deep, and create a thick mat which prevents seeds and seedlings of other plants from establishing themselves.
Not only does this monster thrive in woods and along rivers and streams, but it can dry out the soil it lives in and out-compete some of our region’s endangered plants. Yellow flag can clog irrigation systems, drainage pipes and ditches. It can alter the course of streams and rivers by trapping sediment. (In fact, it’s been used for erosion control and sediment trapping at sewage treatment plants, but its faults outweigh its benefits.)
The iris can tolerate fresh or brackish water, neutral to highly acidic soil, low levels of oxygen in the ground and either wet or dry environments. Its seeds can float for up to two months and last in high salinity for over a month, enabling them to travel great distances. Pieces of its rhizomes can float, then re-root in a new place.
Yellow flag, tagged as a nonindigenous aquatic species (NAS) by the U.S. Geological Survey, grows wild in more than 40 U.S. states and is listed as invasive in most of them. Native to Europe, North Africa and parts of the Middle East, it was introduced to eastern North America as an ornamental in the late 1700s, according to the Maryland Invasive Species Council. By the 1950s, it had spread to the West coast.
To remove the invader from your garden, small clumps can be dug up by hand, the Council advises. For big ones, you may need to use a pick-axe and shovel. Another option is a herbicide such as the aquatic formulation of Round-Up or imazapyr.
Amazingly, one can buy yellow flag at some major stores, garden centers and online, despite its illegal status. The site thePondguy offered two plants for $22 but said it was “out of stock” for “the rest of the year.” Well, he can have all of mine for free.
In the meantime, happy gardening!
Laetitia Sands is a master gardener in Dorchester County.

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