PORTSMOUTH — It's invasive, insidious and, come to find out, delicious. Fallopia japonica, better known as Japanese knotweed, is a fast-growing, hard-to-kill perennial, that reaches the height of corn stalks, resembles bamboo and has been known to grow through asphalt and floorboards. It can be found in the Great Bay Natural Wildlife Refuge, lining Seacoast riverbanks and proliferating along local roads. Newsweek last year reported some British mortgage lenders were denying loans for properties with Japanese knotweed because of its deleterious impact on property values.

Douglas Cygan, an entomologist and New Hampshire's invasive species coordinator, calls the knotweed a threat to natural habitats and he's charged with coordinating a statewide initiative to smother and poison it along state roadways.

Tom Lee, plant ecologist with the University of New Hampshire's Department of Natural Resources, said, "I'm concerned about it." Lee cited the prolific nature of the invasive species and its ability to stifle other plant life in its proximity as reasons for his concern. "It is something to keep an eye on," concurred Portsmouth's Public Works Director Peter Rice. "It takes over because it's opportunistic and it's successful."

But at Moxy restaurant in Portsmouth, Japanese knotweed is now on the menu.

Moxy's chef, Matt Louis, recently prepared Japanese knotweed in a fruit pie, pickled and as a sautéed side with salmon and rabbit. Seacoast Media Group staff sampled the pie and pickles and can vouch for their deliciousness.

"Some foods are so overused," Louis said. "This is the next level; eating wild, indigenous and in some cases, invasive plants."

Eats, shoots and leaves

Cygan said he wouldn't eat Japanese knotweed. "I'm sure it's delicious, but I deal with invasive species all the time, so I have no desire."

The state of New Hampshire's expert on Japanese knotweed, Cygan said it's probably the most widespread invasive species and is typically found on river corridors, along streams and lakes and next to roads. A half-inch piece of the weed can spawn a new plant then a grove, while small pieces are spread by ice dams, erosion and lawn mowers.

Cygan has policed and cited people for selling top soil with bits of knotweed which, he said, winds up on a buyer's property where it takes root and spreads. He's also forced nurseries selling knotweed to destroy the plants.

"Once it's out of the ground, you have to kill it," he said.

Cutting Japanese knotweed stimulates more growth, as the rhizome root systems grow underground, sprout new shoots and make new plants, he said.

Mowing knotweed along state highways is prohibited because mowing decks transfer the plants to new locations, Cygan said.

On the Seacoast, he's launched efforts to kill knotweed along routes 1A and 1B. On oceanside roads, Cygan said, he's killed pockets of knotweed growing between roads and the ocean. If there's a grove that spreads onto private property, he said, he doesn't bother because if homeowners aren't taking efforts on their side, it's pointless.

One town cut and stockpiled knotweed, after which shoots formed from the pile and a new population developed, he said.

Portsmouth's Public Works director Peter Rice said he hasn't seen its proliferation "rise to the point of crisis." City workers have offered removal assistance on private properties where they abut city-owned land, he said.

UNH's Tom Lee said knotweed throws shade over native vegetation and grows "remarkably quickly in the spring." It has a "very thick canopy" and lots of leaf layers, he said, shading everything beneath it so "there's very little else going on and it reduces the diversity of other plants."

"This plant is not widely consumed by native creatures, so it doesn't create a great wildlife habitat," Lee added. "It’s a herbaceous plant that dies back in the fall, so it doesn't do a great job stabilizing the soil, so it really has changed our riversides."

Lee said there's not a lot of data on the effects of knotweed, so it's hard to predict the long-term impact. He said he has checked references and determined that "we need to know more."

To tame the spread of the knotweed, Cygan said he's killed a combined 47 acres of it over the past three years using herbicides. Common Roundup is effective to kill the plants, but only works if it's applied on the leaves in late summer, Cygan said. The other killing method involves cutting it at the base, then covering the area with layers of plastic sandwiched between layers of mulch or sawdust for a period of five years.

Cygan said New Hampshire is the only state in the country with invasive plant control and was the first to ban invasive plants from being sold.

Because knotweed is "very aggressive," Lee said, eating it is "a great use for these invasive plants."

'Eat something else'

Chef Matt Louis recently put freshly-foraged Japanese knotweed on his menu at Moxy and, according to his dining room manager, not a single diner mentioned it as a roadside weed.

Louis' strawberry-knotweed pies taste no different than if the knotweed was rhubarb. His knotweed slices — pickled in rice wine vinegar, sugar and water — are tender and tasty. "I think it's fun and interesting to learn about indigenous foods," said Louis, who asked why people are "stuck" eating the same foods. "Eat something else."

But he warned, don't harvest it from the side of a road where it could be exposed to toxins. "It's important to know your source," said Louis, who gets his Japanese knotweed from Fileshea White, one of his foragers.

She, like his other foragers, keep secret the spots where they harvest knotweed, as well as nettles, wild clover, ramps, baby spring onions and fiddleheads used by local restaurants. Garlic mustard greens are "everywhere," said Louis, pointing out the window of his Penhallow Street restaurant while saying, "You could probably find some out there across the street."

Louis said he makes a pesto from dandelion greens and last week’s sautéed Japanese knotweed that was served with pollock.

"It's exciting," he said. "This is really fun for me, to work with indigenous plants. I want to go deeper."

White said she's a self-taught forager and advises that Japanese knotweed is best when picked "really young." "If you get them bigger, they get pretty woody," she said.

Knotweed is rich in vitamins A and C and is full of potassium, she said. In spite of that, White said, people "spray it with pesticides" to try and kill it.

"Eating it is also weed control," said White, who believes that understanding plants "is part of understanding the world around us."

When she brings a batch of Japanese knotweed to Moxy, Louis covers it with a damp towel and said it keeps in a cooler for about a week. He's putting it on his menu, paired with other "user friendly" foods, "so you slowly introduce people."

"If I put a knotweed salad on the menu, I wouldn't sell one," he said. "We have a world hunger problem and we have all of this free food."

Originally published on Seacoastonline.com on May 27, 2015

Photo Credit: E. Spinney

Synonyms for Japanese knotweed: Fallopia japonic, Polygonum cuspidatum, bamboo