Sunday, September 13, 2009

Beware the invasive plant:Knotweed

There are at least three kinds of invasive knotweeds – Bohemian, giant, and Japanese knotweed. (latin names: Polygonum x bohemicum, P. cuspidatum, P. sachalinense). All have similar characteristics – they are incredibly invasive and incredibly hard to kill.

This time of year, knotweed is particularly noticeable in the native landscape because it is flowering. I am not sure which type of knotweed this is. The picture was taken on a recent hike on the MA & PA trail in Harford County, Maryland.

Because these plants are so prolific, they crowd out native species. And because they spread by runners, they are hard to contain.

Here is some great information on how to eradicate.

Believe it or not, this plant is still sometimes sold as Fallopia japonica. Growers indicated that this is a hybrid and does not have the invasive qualities that traditional knotweed does. However, a quick review of the garden boards shows that people have problems keep control of the hybrid as well.

I admit, this plant is somewhat attractive, but there is no need to plant it! There are plenty of great, non-invasive alternatives. One idea from the great book Native Alternatives to Invasive Plants is Aruncus dioicus, commonly known as Goatsbeard.

photo credit: Gideon Strauss

For more information on Goatsbeard, check out this site. And here are some more ideas for native alternatives to knotweed.


  1. I believe I have a Bohemian Knotweed. I've had this one plant for about 7 years and it has never spread. In fact the "mother" plant I took a shoot from has been in the same place for...well it was there when I bought my house almost 17 yrs ago and that plant has not spread at all. It looks so nice against the fence where it's been growing. It's clump and mine have only 10 shoot/stems, never more than that. I live in North Worcester County, MA.

  2. To ad to my previous post Anonymous.
    My Mother in law's neighbor had Japanese Knotweed which spread under ma's fence and it took us years to get rif of it. That plant had red stems and veins, mines does not.