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Peterborough

Battling the invaders

Peterborough: Locals go to war with invasive plant species like garlic mustard and knotweed

  • Conservation Commission members and Well School students pulled up invasive garlic mustard plants at the school on Saturday.
  • Conservation Commission members and Well School students pulled up invasive garlic mustard plants at the school on Saturday.
  • Conservation Commission members and Well School students pulled up invasive garlic mustard plants at the school on Saturday.
  • Conservation Commission members and Well School students pulled up invasive garlic mustard plants at the school on Saturday.
  • Conservation Commission members and Well School students pulled up invasive garlic mustard plants at the school on Saturday.

PETERBOROUGH — The garlic mustard plants alongside the driveway into the Well School look pretty innocuous. Growing low to the ground, they have pretty green leaves that are sprouting through the fallen leaves that line the road after a long winter. Chewing on a leaf, one doesn’t taste much garlic — or mustard for that matter — although a few leaves could certainly be a tasty addition to a mixed green salad.

Unfortunately, garlic mustard is spreading rapidly throughout New Hampshire, often after being introduced when highway departments or landscapers put down roadside fill. The problem is that as the fast growing plant spreads into nearby forest land, it crowds out native wildflowers and its roots release a chemical that will impede the growth of trees. It has no insect or disease predators and by its second year can grow to four feet tall and produce between 100 and 1,000 seeds.

“I’ve been watching garlic mustard around here for about four years now,” said Francie Von Mertens, a Peterborough Conservation Commission member who helped organize a garlic mustard pull on Saturday at the Well School. “It’s really spreading. The whole point of what we’re doing is early detection and early removal.”

As Von Mertens spoke, Conservation Commission members, Well School students and parents and members of the Von Mertens clan quickly filled large plastic buckets with clumps of garlic mustard. They simply grasped the plants, which bloom around this time of the year and produce clusters of 4-petaled white flowers, by the roots, easily pulling them out of the soft soil. Amy Wilson, who teaches at the Well School, said students had filled eight five-gallon bags with garlic mustard earlier in the week, just from the school’s property.

Von Mertens said she’s seen the plants nearby on the side of Middle Road and at several other spots in Peterborough.

“People need to be aware of this and to be careful about where they get their fill,” she said.

Garlic mustard is just one of the invasive plants that Von Mertens identifies as the “dirty dozen” in a brochure that she was passing out on Saturday. Another priority, in her opinion, is to deal with Japanese knotweed, which also is often introduced through roadside fill. Knotweed, also known as false bamboo, grows tall and has bulbous roots that don’t anchor soil, so it can lead to erosion along streams. The best way to get rid of it is to use a spade fork to dig it out completely, including the roots. If they become established, knotweed plants can be cut across the base, which will weaken the plants.

Some of the plants on the dirty dozen list were once popular for landscaping. The brochure, which was produced by the Peterborough Conservation Commission, has a picture of two Norway maple trees that were planted in front of the Peterborough police station by the Conservation Commission before people became aware of the dangers of invasive species. The Norway maple has now been found to compete with sugar maples and can quickly shade out other plants. Burning bush plants can still be seen all over, even though new plantings are now prohibited in New Hampshire. Oriental bittersweet has decorative berries, but it’s a climbing vine that can grow up to 60 feet tall, choking the plant or tree it’s growing on.

The list of invasive species varies widely in different regions of the country, said Von Mertens. Scotch broom, for example, is classified as an invasive species in California and the Pacific Northwest, but it’s not a problem in New England and plants can be purchased locally. And the list is constantly changing. The Conservation Commission brochure warns people to watch for the black swallow-wort vine, a member of the milkweed family that could be headed our way.

Von Mertens urges people to pick up one of the brochures from Conservation Commission members or at the Peterborough Town House.

“People need to know about these plants, and to spread the word,” she said.

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