Rent Shop Volunteer Join

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
2 ratings

Monday - August 03, 2009

From: Franklin, TN
Region: Southeast
Topic: Trees
Title: Annuals victims of allelopathy under a hackberry tree in Franklin TN
Answered by: Barbara Medford

QUESTION:

In our new home's back yard we have a 30' hackberry tree that's less than 20' from our house, on the NW side. I planted your typical shade annuals, impatiens, etc., in the mulch bed under the tree and they fared quite poorly this summer. I read your comments to Joe Marcus on 3/25/09 re allelopathy. My question is, what can I plant to avoid this problem? Would it help to plow worm casting mulch into the bed? thanks

ANSWER:

Joe Marcus is one of the Mr. Smarty Plants team; he was answering that question about allelopathy and hackberries, not asking it. We will repeat the pertinent paragraphs from his previous answer.

"Every plant that puts down roots in the earth compete in some way with its neighbors; some compete more aggressively than others.  The rhizosphere, that is, the soil where roots grow, can be thought of quite accurately (if not a bit simplistically) as a war zone.  Plants, animals, fungi and microorganisms living within the rhizosphere continually struggle with one another for their share of the resources available there.

Many trees and other plants interfere with their competition through one of a multitude of processes known collectively as allelopathy.  Allelopathy typically involves living or dead and decaying plant parts exuding, volatilizing or leaching chemical compounds that are inhibitory or harmful to nearby plants.

Hackberry trees, Celtis spp. are known to inhibit the growth of competing plants through allelopathic processes.  The mechanism used by hackberries involves the release of a witch's brew of chemicals known as phenolic phytotoxins leaching from fallen, decaying leaves.  The leachates from rotting hackberry leaves have been shown to inhibit the germination of seeds and the development of seedlings.  So yes, hackberry can do harm to nearby plants, though it is unclear if it has any effect at all on established plants such as trees, shrubs or even mature perennials." 

In answer to your question, it is more likely that the shade and litter from the hackberry caused the problems with your (non-native) impatiens and other annuals. It also has a lot of roots up close to the surface, and those annual roots are competing with much sturdier and older hackberry roots. In a case like this, worm castings or fertilizer are probably not the solution, although the hackberry roots would probably love it. Sometimes you have to choose: do you want the tree or do you want the plants under it?

In defense of the tree, Celtis occidentalis (common hackberry), it is perhaps not the most beautiful tree, and deciduous, but did you know that it is a food source for the Wild Cherry Sphinx Moth, and a larval host for the Tawny Emperor, American Snout, Question Mark and Mourning Cloak butterflies? The mulch that you mentioned is a nice ground cover under a tree, and you won't have to replant the annuals every year. Perhaps there is room for a bed of annuals farther away, where there is no large tree defending its territory. 

 

More Trees Questions

Keeping squirrels out of pecan tree from Garland TX
August 17, 2013 - My yard is covered in green pecans with one bite eaten by squirrels. How do I keep squirrels out of my pecan tree?
view the full question and answer

Problems with Monterrey Oak in Austin
March 26, 2013 - We had a local tree service plant two Monterrey Oak trees on 4/2/2012. At the time we noticed that woodpeckers had had a field day on the trunk bark of both trees with the most damage being on the lar...
view the full question and answer

What about Asian Jasmine and scrub oaks?
September 01, 2010 - Dear Mr. Smarty Plants, I have several clusters of native scrub oaks in my yard. I planted Asian jasmine under them many years ago. The trees look fine, but an arborist has told me that the Asian ...
view the full question and answer

Fruit trees for Bellville, TX
January 03, 2010 - Which fruit trees will withstand heat and drought in the Bellville, Texas area?
view the full question and answer

How to prune my Linden tree?
June 17, 2009 - We have a 15 yr old Linden in the backyard. North side of home. It can use some pruning at the lower branches. Which branches do we prune and when? Also we have some river birches back there. Oth...
view the full question and answer

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