En EspaŅol

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
1 rating

Saturday - August 10, 2013

From: Chippewa Falls, WI
Region: Midwest
Topic: Invasive Plants, Shade Tolerant
Title: Plants to replace Polygonum cuspidatum ( Japanese knotweed)
Answered by: Nan Hampton

QUESTION:

I live in a heavily wooed area of Chippewa Falls, WI. Our property is covered with Giant Japanese Knot Weed. We have been trying to get rid of it for years. We are finally going to try using the dreaded, Round UP, after trying many natural techniques and solutions over the years to no avail. Even covering them up with dark AND clear plastic sheets hasn't worked. We are wondering what sort of fast growing/spreading ground cover we could plant to try to crowd out what may survive of the knot weed once we use the chemicals. What might we seed the area with that would be native to our area? We have deep shaded wooded areas, with a few depressions of standing water with hard rains. Also have shady and sunny areas up next to the house where the knot weed is prolific. Thank you for any suggestions.

ANSWER:

Polygonum cuspidatum [synonym=Fallopia japonica] (Japanese knotweed) appears on the Plant Conservation Alliance's (PCA) Alien Plant Working Group's LEAST WANTED list.  Please read their "Management Options" sections for control methods.  The USDA Plants Database has a distribution map for North America plus a list of states (under "Legal Status") where it is considered prohibited, banned, invasive or noxious.  We do understand you have a serious problem here.  There is an Invasive Plants Association of Wisconsin that has a website with a great deal of useful information, including a list of Regional and County Groups that deal with invasives in Wisconsin.

Now, with that said, finding species that will "outcompete" this very tough plant (according to the PCA's LEAST WANTED web page "can tolerate a variety of adverse conditions including full shade, high temperatures, high salinity, and drought") is not going to be an easy task.   We can recommend species that will do well in the conditions you give for your site, but you are going to have to continue to be vigilant and deligent in removing/destroying the knotweed as it reappears.  Sorry to deliver that bad news—but you probably already realized that was going to be the case.

Let's start with suggestions for the deep-shaded wooded areas with moist soil:

Arctostaphylos uva-ursi (Kinnikinnick) is a trailing evergreen shrub that makes a good groundcover in shady areas.  It will also grow in sun and part shade.

Adiantum pedatum (Northern maidenhair) and Athyrium filix-femina (Common ladyfern) are deciduous ferns.

Cornus canadensis (Bunchberry dogwood) makes an excellent low groundcover in shady woods.

Dryopteris cristata (Crested woodfern) is a partially evergreen fern that grows in sun, part shade and shade.

Hydrophyllum virginianum (Eastern waterleaf) grows in part shade and shade in moist woods and is labeled as an "aggressive grower"—a good candidate for competing with the Japanese knotweed.  Here are more photos and information from Robert W. Freckman Herbarium University of Wisconsin.

Polystichum acrostichoides (Christmas fern) is an evergreen, clumping fern.

Chasmanthium latifolium (Inland sea oats) is one of the few grasses that grow well in shade.  It is said to be aggressive in spreading.  Here is more information from Missouri Botanical Garden.

Carex plantaginea (Plantainleaf sedge) is an evergreen grass-like plant.  Here is more information from Illinois Wildflowers.

Lycopodium digitatum (Fan clubmoss) is an evergreen, low growth plant with a spreading habit.  Here is more information from Illinois Wildflowers.

You can search for more possibilities by doing a COMBINATION SEARCH in our Native Plant Database.  Choose "Wisconsin" from Select State or Province, "Shade" from Light Requirement, "Moist" from Soil Moisture and both "0-1 ft" and "1-3 ft" from Size Characteristics.  You, of course, can change or add characteristics for your search.  For instance, choose "Sun" from Light Requirement for the areas near your house.

Prairie Nursery in Westfield WI has Native Ground Covers for sale as well as other native plants.  Prairie Moon Nursery in neighboring Minnesota has native seeds and seed mixes for sale (e.g., Shady Woodland Seed Mix for Wet Mesic to Dry Mesic Soils).  You can find more nurseries and seed companies that specialize in native plants in your area by search in our National Suppliers Directory.

 

From the Image Gallery


Kinnikinnick
Arctostaphylos uva-ursi

Northern maidenhair
Adiantum pedatum

Common ladyfern
Athyrium filix-femina

Bunchberry dogwood
Cornus canadensis

Crested woodfern
Dryopteris cristata

Eastern waterleaf
Hydrophyllum virginianum

Christmas fern
Polystichum acrostichoides

Inland sea oats
Chasmanthium latifolium

Plantainleaf sedge
Carex plantaginea

Fan clubmoss
Lycopodium digitatum

More Shade Tolerant Questions

Understory Shrubs for Pennsylvania Clay
December 04, 2013 - I want to replace three non-native Euonymus alatus with native shrubs that will serve as host plants for butterfly/moth species and/or attract bumblebees and other native bees. The shrubs I have are ...
view the full question and answer

Plants for shade
August 19, 2008 - I live in hot, humid Houston and the tree coverage of my yard is nearly 100 percent (so, little sunlight reaches the ground). Can you suggest a plant or two that would thrive in these conditions?
view the full question and answer

Disagreement with HOA on raised beds placed beneath mature oak from Tequesta FL
April 05, 2014 - I have mature 30 year old oak trees on my property and I put a raised bed under each with very good soil and I used pavers for retaining the soil about about 1.5 ft high. I planted a perennial begonia...
view the full question and answer

Container plant for shade in Austin
August 07, 2010 - I am very new to gardening (have already killed two plants on my front entryway), and I looking for a couple recommendations for for a potted plant that I can place on my entryway porch. It is shaded...
view the full question and answer

Hanging flowering plants in part shade in Denton, TX
September 18, 2008 - Dear Mr. Smarty Plants, I'd like to hang 4"-6" pots with flowering plants from north-facing eaves. That area gets an hour or so of late-morning/noon sun. Also, my apt. faces a large courtyard so...
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
© 2014 Lady Bird Johnson Wildflower Center