En EspaÑol

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
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
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

Eliminating weeds from seeded wildflower stands
June 25, 2007 - We live in Eastern Central Texas in a small community on Texas Highway 7. Last fall, we went to the Wildseed Flower Farm near Fredricksburg and purchased a bag of mixed wildflower seeds and planted...
view the full question and answer

Need something to compete with Virginia wild rye in Bristol, TN.
July 29, 2011 - I have been working for 4 years to convert a large area of sunny lawn (150' x 40') to a native woodland planting, using native trees, shrubs, flowers and grasses. Although I used seeds of a variety ...
view the full question and answer

Controlling poison oak or poison ivy in Iowa
April 29, 2010 - We recently purchased a property that is VERY wooded and has been vacant for two yrs. with little upkeep previously. We have (we were told) l00 yr old poison oak vines hanging from trees. We hired so...
view the full question and answer

Controlling Passionflora Incarnata propagation
March 20, 2012 - Would a cinderblock raised bed, 8 inches in height, be sufficient to contain the roots of passiflora incarnata and keep them from traveling to places where I don't want the vine? Are the roots deepe...
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

Smarty Plants's Facebook profile Support the Wildflower Center by Donating Online or Becoming a Member today.

Mr. Smarty Plants wants you to be his Facebook friend. Click the Facebook icon to add yourself to Mr. Smarty Plants list of friends.
E-NEWSLETTER | BECOME A MEMBER | DONATE NOW | MEDIA | SITEMAP | STAFF
© 2015 Lady Bird Johnson Wildflower Center