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?


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
Not Yet Rated

Sunday - March 24, 2013

From: Dallas, TX
Region: Southwest
Topic: Compost and Mulch, Diseases and Disorders, Trees
Title: Allelopathy of American elms from Dallas
Answered by: Barbara Medford


Are American elms at all allelopathic?


There are four members of the genus Ulmus (elm) native to Texas and in or near Dallas County:

Ulmus alata (Winged elm)

Ulmus americana (American elm)

Ulmus crassifolia (Cedar elm)

Ulmus rubra (Slippery elm)

Black walnut isn't the only tree that produces juglone. This chemical is also secreted in smaller amounts by English walnut, hickory and pecan trees.Other trees with allelopathic properties include tree-of-heaven, sugar maple, hackberry, American sycamore, American elm, southern wax myrtle, cottonwood, black cherry, sassafras, red oak and black locust.

Certainly, in our experience, members of the Juglandaceae family (most familiar - walnuts, pecans) are the most prominent examples of allelopathy, but the American elm is definitely included as being able to deal with competing plants with chemicals. Please note that it is difficult to impossible to grow anything under any tree, including grass, because of the needs of the tree roots for moisture and nutrients from the soil and because of the shade from the tree. Here in Texas, we would vote for the trees and spread mulch under the shade of the tree. See our How-To Article Under Cover with Mulch.


From the Image Gallery

Winged elm
Ulmus alata

American elm
Ulmus americana

Cedar elm
Ulmus crassifolia

Slippery elm
Ulmus rubra

More Compost and Mulch Questions

Conditions for growing Anacacho Orchid in Smithville TX
January 24, 2011 - What conditions (soil type, sun/shade, understory? etc.) to grow a healthy Anacacho Orchid tree? And what is the best size tree to plant?
view the full question and answer

Wax myrtle problems from Driftwood TX
September 04, 2010 - We planted 27 wax myrtles on the perimeter of our property last year and were diligent about watering them throughout the drought. They are in very rocky soil (we had to use a jackhammer to dig the ho...
view the full question and answer

Leaf browning on blackfoot daisy in Arizona
August 26, 2008 - Blackfoot daisy plant was doing great; then, in one day, it turned brown like it had no water. Have a watering system in place which waters once a day for one hour 1/2 gallon a hour.
view the full question and answer

Ground cover for sun in Phenix City, AL
April 04, 2011 - I live in Phenix City, AL and am new to planting. I have a 60 x 15 feet slope that is just dirt. I am going to till it next week and want to plant some various ground cover plants (that will grow to c...
view the full question and answer

Failure to come up of blackeyed susans in Lancaster PA
June 28, 2009 - My blackeyed susans have been blooming for ten years. All of a sudden this year they didn't come up at all..why?
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.
© 2015 Lady Bird Johnson Wildflower Center