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?

Share

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
3 ratings

Monday - July 28, 2008

From: Washington, CT
Region: Northeast
Topic: Invasive Plants, Problem Plants
Title: How to get rid of Japanese knotweed (Polygonum cuspidatum)
Answered by: Nan Hampton

QUESTION:

We have an enormous stand of japanese polygonum that we are trying to get rid of. What soil type is the most inhospitable to this aggressive and highly invasive species? Were thinking of planting some native white pines in the area to grow over them as well as manually digging them out. What would you suggest? Thanks.

ANSWER:

Polygonum cuspidatum (Japanese knotweed) is on the Least Wanted list of the Plant Conservation Alliance's Alien Plant Working Group. It appears from their description that nothing is inhospitable to this plant. As their web site states: "Japanese knotweed can tolerate a variety of adverse conditions including full shade, high temperatures, high salinity, and drought." Planting Pinus strobus (eastern white pine) over the area where the Japanese knotweed grows is a very nice idea, but it won't affect the status of the knotweed. Digging them out is the most environmentally friendly way to get rid of them; and, depending on the size of your population, it might be the best way to eliminate your plants.  The Plant Conservation Alliance also gives specific instructions on chemical treatment for large or difficult populations. The Nature Conservancy and Clark County, Washington also have information on control programs and their success.

 

 

More Problem Plants Questions

Zinc tolerant plants for sunny area
June 08, 2012 - I have a very high zinc soil in an all day sun area. Any suggestions as to what kind of flower can I grow successfully? Zone 8 Thank you
view the full question and answer

Controlling Devil's Bit in Collin County, TX
June 05, 2015 - I live in Collin County and our pasture has a growing section of Devils Bit taking over everything. I've been using 2,4-D on it with some success. What is the best method of control for this ...
view the full question and answer

Removal of thistles from Columbus TX
May 20, 2014 - I am sorry if you have an answer in FAQs but I could not find it. We recently cleared property near Columbus Texas of many cedars (ash junipers). This spring we experienced a profusion of thistle -...
view the full question and answer

Acre-scale Grass Removal near Austin, TX
July 04, 2014 - How do I get rid of 10 acres of Kleingrass?
view the full question and answer

Controlling Cnidoscolus texanus (Texas bullnettle)
July 18, 2013 - Hello,I need your help to control some nasty weeds in my yard/pasture. I am an old timer and do not have a picture to include—haven't figured out that part of the camera/phone yet. This weed is a pri...
view the full question and answer

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