Invasive action in town and at home

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Solarizing strategy to control invasives at Holcomb Farm, Salmon Brook (aka “cooking” mugwort and knotweed under plastic). Submitted photo

Local Action!

Invasive Plant Activists (IPAs) now gather monthly on the second Saturday morning to control invasive plants and allow natives to flourish.

IPA volunteers make friends, learn together and get great results in publicly visible areas. In March and April IPAs focused on three sites at Holcomb Farm: a row of statuesque shagbark hickories on Day Street South, the path to the CSA field and at the bridge over Salmon Brook

The Salmon Brook site is experimenting with a new “solarizing” technique. In a few short years the area has become completely dominated by Oriental knotweed and mugwort, super rapacious invasives —see the April and September 2020 Not Wanted columns in the Drummer for details. In April the IPAs leveled last year’s growth of both plants and then spread clear plastic over the area, heavily weighed down with river rocks. Hot sunny days will raise the underground temperature to over 100 degrees, roasting the plants right down to the roots.

Knotweed is so vigorous that in places it shrugged off the plastic and needed to be covered again. By now it may be cooked rare, while the mugwort appears to be well-done. In a couple months the IPAs will remove the plastic and replace the imported invasives with native plants. A companion strategy is also being tested on nearby clusters: cutting repeatedly throughout the season, over several years, to exhaust the plants’ resources.

In May the IPAs attacked the rapidly expanding infestation of garlic mustard; see the Drummer’s March 2020 Not Wanted column. This biennial invasive spreads rapidly in yards and fields and can be controlled easily over time by pulling it by the roots. June is the perfect time to invite friends and family to a “pulling party” before garlic mustard goes to seed and starts thousands more new plants. Repeat next year and the year after because the seeds remain viable for several years.

To join the IPAs or stay informed, send a note at the GranbyInvasivePlants webpage.

Invasives of the month – June

  • June is a great month to use non-chemical methods to control very vigorous invasive plants. Solarize large concentrations after cutting to the ground, or attack plants individually.
  • Bittersweet: Pull seedlings and small vines by their telltale orange roots. Cut big vines near the ground.
  • Multiflora rose: Pull young plants by the roots. Cut and trample larger ones before they go to seed.
  • Barberry: Don’t plant: all varieties are invasive. Pull young plants by the roots. Cut larger plants low to the ground (bright yellow stems).
  • Winged euonymus: Don’t plant: all varieties are invasive. Pull young plants. Cut larger ones.
  • Autumn and Russian olive: Pull and cut to the ground.
  • For more information on invasive plants and what you can do to control them visit