Host an Event Volunteer Join Tickets

Support the plant database you love!

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

Need help with plant identification, visit the plant identification page.

rate this answer
Not Yet Rated

Monday - September 01, 2014

From: Pleasant Valley, NY
Region: Northeast
Topic: Non-Natives, Problem Plants
Title: Aggressive Plants in Pleasant Valley NY
Answered by: Larry Larson


Are there any native plants that can out compete Japanese knotweed?


Mr Smarty Plants has been chewing on this question a bit.  We are all about the sustainable use and conservation of native wildflowers, plants and landscapes.  Japanese Knotweed [Fallopia japonica] is an import from Eastern Asia and Japan and is renown for its aggressive nature.  As such, it’s both non-native and an invasive species, so it’s not in our records.

  My first reaction to your question is “unlikely to no”.  These links from a search on “Japanese Knotweed” indicated that it is a highly successful invader that crowds out native plants and that it is extremely hard to eradicate.

Fallopia Japonica from Wikipedia

National Invasive Species Record 

Eradication of Japanese Knotweed Plants

And here is the report from the New York Invasive Species Clearing House

The end result of this is that all the experts agree that this is one of the most aggressive invasive species that is present in the US!
  I imagine that the question behind your question is that you have a small infestation of the stuff [I hope not!] and would like to control it.  The process suggested above is to regularly cut it down so that it cannot active spread further, limiting its growth.   It’s possible that some aggressive native plants, such as Campsis radicans (Trumpet creeper) might be competitive, but then you would have two really aggressive plants present and no relief indicated!

  Still looking for a way to say “yes” to you:  Based on the really general nature of your question, we can go a bit farther afield in theory and note that Fallopia Japonica also has a range of territory and climates where it is acclimated.
  It is adapted to Coastal Asia and Japan. This USDA link illustrates that it invades a similar climate range in North America, and that it does not extend to Florida, the desert Southwest or to the frigid North.  So – The native plants that CAN outcompete the Japanese Knotweed are the cacti of Southern Arizona/Nevada, pure Florida natives, or natives to the Yukon – when the invaders vitality is compared to them in their own ecoregion! 



From the Image Gallery

Beavertail prickly pear
Opuntia basilaris

Trumpet creeper
Campsis radicans

Saskatoon serviceberry
Amelanchier alnifolia

Saskatoon serviceberry
Amelanchier alnifolia

More Problem Plants Questions

Toxicity of catalpa wood?
June 05, 2012 - Is the sawdust from cutting up a catalpa tree or the smoke from burning the wood toxic? Thank you,
view the full question and answer

What is the plant called wingspan?
September 21, 2014 - I have a lot of environmental allergies and saw a positive result for "wingspan" yet I cannot find ANY information online about that particular plant. I was told it's "tumbleweed" by the medical ...
view the full question and answer

How do you get rid of Mexican Petunia?
July 21, 2009 - How do you get rid of Mexican Petunia?
view the full question and answer

How Can I Tell an Invasive Thistle from a Native
May 01, 2012 - Mr Smarty Plants, I have some thistles coming up in my yard. I'd like to keep them if they are native, but not if they are invasive or non-native. How can I tell? My yard is a wild area in West Lak...
view the full question and answer

February 17, 2015 - This question may have more to do with chemistry than botany but I thought I would start here. My sister recently discovered that behind her Chili pequin plants, the brick was being dissolved leaving ...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.