Dorchester has mixed record on invasive plants

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Japanese knotweed, a terrible invasive found in most parts of the country,blooms in Maryland this month and in August. If it turns up in your garden, pull it out pronto and dig up all the roots you can. It grows at frightening speed and smothers all vegetation in its path.

On a recent visit to North Carolina, I drove through miles of breathtakingly beautiful mountain scenery where exotic-looking large leaves blanketed a river’s steep banks. Nothing but the luxuriant, abundant foliage of this one type of plant could be seen growing. It was as though green lava had erupted from a volcano and engulfed everything in its path — trees, shrubs, rocks, even a sign for the lakeside village where I was headed.

Hills and humps covered in the same leaves were all that remained to indicate the southern Appalachian landscape, in all its diversity, that had once existed before being swallowed up. Surely this was an invasive plant, but one I didn’t recognize.

A walk along a picturesque path bordering the Broad River gave me the answer. Signs identified the plant as Japanese knotweed, along with an explanation of how invasives devastate native ecology and an appeal to the public to help combat the green enemy.

On return home to Maryland, I googled Japanese knotweed and discovered that it grows in Dorchester, too. While the invasives we’re more familiar with may be phragmites, the tall reeds that take over our wetlands, and mile-a-minute, seen along many roadsides, Dorchester County has had more reported sightings of Japanese knotweed than any other county in Maryland except Wicomico and Caroline counties. The information, updated this year, came from the website

This month and August are when Japanese knotweed blooms in Maryland, so keep your eyes peeled and you may spot it. Yet, fewer species of invasive plants in general have been reported in Dorchester than in almost any other Maryland county – 82, according to the Center for Invasive Species and Ecosystem Health, an organization formed by the University of Georgia.

Eighty-two sounds like a lot to me, but the only counties which scored better were Queen Anne’s, which had 69 invasive plant species, Baltimore city (56) and Somerset (47). Worst was Kent County, with 110 reported.

Of course, the statistics are based on reports of plant sightings, so they’re subject to variables which may seriously reduce their accuracy. Who does the reporting? Do they cover entire counties? Perhaps the degree of reporting varies from county to county. Still, the statistics can be taken as some sort of yardstick.

Citizens, especially gardeners, should report invasives whenever they spot them because these plants are a huge threat to our ecology and all the wildlife that lives there, as well as to our economy and our personal assets. (The Maryland Department of Agriculture asks people to call: 410-841-5920 to report a suspect invasive plant pest in Maryland).

Japanese knotweed, dubbed the “Godzilla plant” by a landscape gardener whose experiences with it I read about online, can break through concrete, wreck flood defenses, and damage retaining walls, roads and foundations. This is in addition to smothering any form of plant life that stands in its way and creating a monoculture or single-plant landscape.

Animals, birds and insects depend on a multitude of plants for food and shelter, in other words: biodiversity. Take away biodiversity and you condemn countless forms of life to flee – if they can — or die. That’s not to mention the demise of all the plants, mosses and fungi that exist in a particular environment before an invader moves in.

World’s Worst Invasive Plants found in Dorchester

Listed by the World Conservation Union as one of the planet’s worst invasive species, Japanese knotweed, also known as fleeceflower, thrives in at least 39 U.S. states. It can grow 10 to 13 feet taller and 23 feet horizontally in a single season and survives temperatures as cold as minus 35 C (minus  31 F). Originally from East Asia and brought to England in the 1800s as a garden ornamental, it’s classified as invasive on several continents.

Britain spent the equivalent of $130 million trying to eradicate the plant from land slated to be used for the 2012 Olympic Games. For a while, British banks refused to give mortgages to people whose prospective homes had Japanese knotweed growing in the garden or nearby.

In Australia, it’s illegal to have Japanese knotweed growing on ones property. In Canada, the invasive has been found in all but two provinces. When city workers in a town in British Columbia tried to eradicate it by digging three meters (almost 10 feet) into the ground with an excavator, the plant grew back twice as large the following year!

Because the plant’s roots burrow so deep and can regenerate from a piece the size of ones fingernail, removing the roots is labor-intensive and sometimes inefficient. Yet, it’s considered quicker than trying to poison the plant. Only two herbicides are believed effective  – glyphosate (RoundUp) and imazapyr, or a combination.

Experts say the best way to control Japanese knotweed (notice, they don’t say “kill”) is to apply a systemic herbicide to destroy the roots, as well as repeatedly chopping up its stems and leaves. The treatment must be repeated over several years, but it’s not necessarily effective in the long-term. It’s also difficult to dispose of the debris without inadvertently spreading the invasive.

Another method is to cover the plant with heavy plastic, lots of newspaper, old carpeting or concrete, then add mulch. One can then place a raised bed or containers with plants atop all that. But if the Godzilla leaves find a crack anywhere, they’ll grow through.

Currently, biologic pest agents – a leaf spot fungus and an insect that prey on the plant in its native region – show promise, according to experts.

Of course, like any bad character, Japanese knotweed has its good side. The Japanese eat it as a spring vegetable, but cooking it involves lengthy preparation and the plant, which, like rhubarb, contains oxalic acid, may aggravate conditions like arthritis, gout and kidney stones. (One of the plant’s many names is donkey rhubarb).

Manufacturers of health supplements use the plant as a source of resveratrol and its glucoside piceid, elements also found in grapes.

Finally, goats and perhaps other animals eat the above-ground parts, while pigs like the roots.

More on invasives can be found at:, and

In the meantime, remove invasives when you can, replace them with native plants and happy gardening!

Editor’s note: Laetitia Sands is a Master Gardener in Dorchester County.

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