Town Center Project Facing a New and Tenacious Enemy: Japanese Knotweed

On a sunny day stroll around the soon-to-be-done (?) Town Center Improvement Project, the Owl noted tiny sprouts of Japanese knotweed coming up in the “hell strips” — the small dirt-covered areas between road and sidewalk–and even in Knox Park. Wherever this fill came from, it has brought a major invader that will be difficult to eradicate.

For those not familiar with Japanese knotweed, it is one of the world’s most invasive plants. It traveled from Japan to the UK and onwards to the US in the 19th century. At one point, it was considered an “ornamental” plant and purposefully put into landscapes. Only later was the insidious unkillability of it noted–it crowds out all other plants and can travel through water. It’s like evil Superman. In a class about invasive plants last year, the webinar participants were advised to just get up and move if Japanese knotweed were found in their yards–it would be easier and cheaper to deal with. The Owl is not entirely sure the professor was joking.

Knotweed can break through concrete, foundations, and yes, even 15″ tall sidewalk curbs. A recent Slate article describes it like this:

 A new plant can grow from a fingernail-size piece of root, and a century of building homes, roads, ditches, and levees—and dumping the dirt wherever it was convenient—helped put those fragments everywhere. So did flooding, which carried bits of root downstream. Barriers like walls and roads were no obstacle because knotweed roots can stretch as far as 70 feet from the nearest stem.Slate

Here’s the bad news for us, Weston. New trees cannot grow in knotweed’s monoculture. It crowds out everything. So what are we to do now that we’ve let the enemy in the gates? Is pulling out this fill and replacing it with clean fill an option? Not sure–it’s possible it’s too late already since rhizomes may be all around.

If the fill cannot be replaced, these are the options:

  • Smothering: This involves putting heavy plastic or tarp over all exposed dirt. This has to be started in spring and the Owl cannot imagine that the town residents, after millions spent on beautifying downtown, will be remotely interested in Hefty bag downtown.
  • Cutting: Repeatedly cutting the knotweed down to the ground will control it but will not rid the area of it.
  • Digging: If the plants are smothered for a period of time, a dig-up can be scheduled immediately after.
  • Herbicide: Yes, the dreaded Rodeo. Again, probably not going to fly in this town.

The provenance of the Town Center fill is beyond the research possibilities of the Owl’s unpaid staff. In a wild and unsubstantiated attempt to find the guilty fill , the Owl did note one suspect for this edition of Special Crimes Unit Weston: the Brush Dump. On a walk around the College Pond Conservation area, it is clear that the land where the brush dump lies is infested with knotweed–as are at least two piles of compost and fill.

Tough to catch on photo: stalks of knotweed behind the pile of fill at the Brush Dump
Knotweed in compost piles at Brush Dump

While the Owl does not know if the fill came from the Brush Dump, the learnings here are for all of us. Know where your fill and your compost come from, lest you find yourself engaged in a battle to the death with Japanese knotweed.


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