Photo by Dave Warner – Japanese Knotweed alongside the road coming into Little Falls on Highway 167.
So says Teri Dunn Chace, who is a writer, an editor, a botanist and horticulturalist with a broad range of expertise and interests, when talking about Japanese Knotweed. “Few plants fill homeowners, landscapers, and botanists with dread like Japanese knotweed does. It’s a bad one—very aggressive, very hard to stop,” said Chace.
Teri worked for 12 years at Horticulture Magazine and is the author of the book How to Eradicate invasive Plants (Timber Press), now lives in Little Falls and she says this is the time of year to go after the invasive species. “It’s a fast grower and forms dense, tall stands. Some people call it Japanese bamboo because, like bamboo, the mature stems are hollow. It has heart or oval-shaped leaves and, in late summer and early autumn, lacy tresses of white flowers,” said Chace.
Chace continued “Left alone, this plant will expand its territory every year. It grows so thickly that nothing else can get in or compete. Native plants are shoved aside, including ones that are important to wildlife like cattails, grasses, and brambles. If you have it in your yard and want to have a garden or even just a lawn or clear driveway, good luck…it can and will stomp all over your plans.”
This plant has several official names, including Reynoutria japonica and Fallopia japonica; an old name is Polygonum cuspidatum. This plant lowers property values as people learn more about the plant and are unwilling to buy properties when the plant is even on a neighbor’s land.
“This plant is invasive all over the northeastern part of North America, from Nova Scotia down the Eastern seaboard to North Carolina. Winter kills the top growth, but then it’s back in the spring with a vengeance,” stated Chace.
Japanese knotweed is able to regenerate from stem and root fragments. Also, the flowers go to seed and blow around, or get transported by birds or animals. It can even cross roads when rainfall carries it across, or can be carried downstream and start anew.
“Highway crews may dump contaminated fill, or a bush-hog can push plant pieces further on down the line. It’s also possible that seeds and plant fragments travel via our pets or vehicle tires,” says Chace.
“This plant is eating roads, farmland, back yards, golf courses, you name it. It was originally imported as an ornamental plant because it’s taller than a person and it was marketed as a living fence,” said Chace. “It was very attractive to people who had a large piece of land and wanted it fenced off, but not when it becomes a pest – a beast of a problem.”
Cutting Japanese knotweed back when it is actively growing in spring and summer isn’t very satisfactory. All of the energy is moving upward and common pesticides like Roundup are not transmitted down into the roots.
Chace says “Cutting back in late summer works best of all. Then, all the plant’s energy is going down—to provide the roots with starch reverses for next year’s resurgence. This is also the time to bring out the weedkiller, if you are willing to use it.”
“We have a terrible problem with it in this town. Head south on Highway 167 just over the bridge and you’ll see it on both sides of the road before 5S,” Chace continues. “You have these big white tresses of lacy white flowers…it is overwhelming this side of town.”
“There used to be a variety of native plants growing there, including berry bushes. You could go out, pick fruit, but stands of this plant are just jamming them out of the way,” said Chace.
How do you get rid of it? According to Chace “Burn the whole plant and roots—only after they have been removed from the ground—in a safe way. Do not leave the pieces in place or dump them anywhere! Definitely do not add them to a compost pile. One idea (this works with any weed) is to bag it all and let the bags sit so the contents break down and dry out, then send it away with the garbage.”
Chace states “This is the perfect time of the year to get rid of it. In the fall, when it blooms, it takes a ton of energy for them to produce their flowers and the plant is at its weakest right now. It’s much weaker than it is in the spring….just wade in and chop it down!”
“It’s such a strong plant in some of these big stands, so you will have to cut it back again and again, year after year, but eventually you can win out,” said Chace.
Some countries are already taking note of the problem and taking harsh measures. In England, if you try and get a mortgage for a house and the property has Japanese Knotweed on it, they will not approve the loan.
“That gives you an idea of just how bad this plant is,” says Chace. “If you wait until October to deal with this, you are too late, because after the flowers, come the seeds and they spread.”
Chace has some tips for prevention:
- Do not buy or use potentially contaminated fill, especially roadside fill.
- Do not leave open areas where it can invade. “Nature abhors a vacuum” and Japanese knotweed will move in to open areas. If you clear out an area, be sure to plant something else or cover it until you are ready to do so.
- Patrol your property. Pull out baby sprouts and dispose of them promptly and correctly.
- Do not let the plant go to seed. As soon as you see the flowers, cut or shear them off.
- If a neighbor has a patch, tell them these things and/or offer to help.
“If we educate people and get them to attack this in their own yard right now, we’ll make some progress. Otherwise, we’ll lose our gardening space, Veteran’s Park, the school….it’s everywhere,” Chace said.