Connecticut’s Invasive Plants

This is a re-post from October 2012, but the information is still valid and important.

What a gardener refers to as invasive might really be no more than a garden thug – a plant that doesn’t understand how to play nicely with its neighbors and aggressively crowds other plants. Garden thugs may be a pain in the root to neighboring plants, or a pain in the gardener’s back – or more southerly bit of human anatomy – but a plant thug may not pass the nine point test required to be named a Connecticut invasive.

To date, 97 different plant species have been added to the Connecticut Invasive Plant list. Each meets the following criteria – all nine of them. The plant

  • is nonindigenous to Connecticut – it was not here before European colonization;
  • is naturalized or has the potential to become naturalized – it’s happy here;
  • has the biological potential for rapid and widespread dispersion and establishment – it can spread easily;
  • has the biological potential for excessive dispersion – it can spread excessively;
  • has the biological potential to exist in high numbers outside of intensely managed habitats – for example, in woods, fields, wetlands;
  • it can be found in wide regions or in particular habitats within Connecticut;
  • it has grown into large stands;
  • it can out-compete other plants;
  • and, it has the potential for rapid growth, high seed production and dissemination, and establishment in natural communities.

This photo of Japanese barberry overtaking a forest floor is a good example of a Connecticut invasive.


Japanese barberry, garlic mustard, Oriental bittersweet, Russian and Autumn olive, Winged euonymus, a.k.a. burning bush, ground ivy, many honeysuckles, moneywort, Japanese knotweed, multiflora rose and sheep sorrel are some of the invasive plants common to Connecticut gardens, as is mugwort, the most recent addition to the Connecticut Invasive Plant list. (The October 2012 update lists mugwort. As of the date of this post, the October 2011 online version, does not.) Many of these plants are so invasive they are found in every Connecticut county.

Of the 97 plant species considered invasive in Connecticut, 80 are illegal to import, move (unless for research, control, or education purposes), sell, purchase, transplant, cultivate, or distribute, according to information provided to attendees at the Invasive Plant Symposium held October 25, 2012 at the University of Connecticut. Notice I said just 80 of Connecticut’s invasives are prohibited. This means 17 can still be sold and purchased, planted and distributed in spite of their invasive label.

Becoming familiar with the Connecticut Invasive Plant list is one way for Connecticut gardeners to garden thoughtfully. It’s much better to identify a plant as invasive before giving it a chance to do its invasive thing in your garden or on your property. It’s also valuable to know how to recognize invasive plants when they first show themselves. Eradication is so much easier when plants are young.


Update: read more about how we control Japanese stilt grass.

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2 comments for “Connecticut’s Invasive Plants

  1. October 5, 2013 at 8:37 am

    Amen! The meadow and hill behind us are rampant with most of the plants you list, and I do know that trying to eradicate them as mature woody plants is an awful job. I try to be vigilant and get the young spreaders in spring but the image of a teaspoon and the ocean comes to mind.

    The only real solution for me seems to be constant mowing all summer (at least areas of the meadow) and densely planted reforestation. I have planted so many trees, and they are now big enough to shade out the garlic mustard, multiflora rose, knotweed, etc. in the narrow area where they grow. But at the sunny edge it’s a battle. And bittersweet doesn’t care about the new forest — it wants the young trunks to climb, shade or not!

    • October 5, 2013 at 1:07 pm

      Laurrie, I take invasive plant strolls beginning in late winter/early spring to catch the first sprouts of invasives such as Japanese barberry, bittersweet, and garlic mustard then again in late May/early June to catch early Japanese stilt grass and any bittersweet, garlic mustard, or other invasives I missed the first time. I repeat the process each month during the summer and into early autumn. So far this has helped keep the most aggressive invasives in our landscape in check, but one must remain vigilant. I pull whatever invasive I see when I see it so it doesn’t get a chance to take over should I become distracted by other duties. This seems to be the only way to keep our property from turning into an invasive-filled landscape.

      The sunnier edges always seem to be a battleground.

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