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?


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
1 rating

Saturday - June 29, 2013

From: San Diego, CA
Region: California
Topic: Poisonous Plants, Problem Plants
Title: Can oleander poison the ground below it?
Answered by: Nan Hampton


Can oleander poison the ground below it? Would it kill/damage grass or other plants below it? Thanks.


It was shown that Nerium oleander (Oleander), native to the Mediterranean region, southeast Asia and northern Africa, did have strong allelopathic effects on seed germination and the growth of radishes when extracts made from oleander's leaves, stems with bark or roots.  [Tran Dan Khanh et al.  2005.  Paddy weed control by medicinal and leguminous plants from Southeast Asia.  Crop Protection.  24 (May 2005) pp. 421-431.]

Another study [Rajyalakshmi, M. et al.  2011.  Inhibitory effects of Nerium oleander L. and Its Compounds, Rutin and Quercetin, on Parthenium hysterophorus L.  Journal of Agricultural Science. 3(2) June 2011.] showed that extracts of oleander leaves significantly inhibited germination and early growth of the invasive weed, Parthenium hysterophorus.

Certainly, oleander has allelopathic effects on vertebrates that ingest any part of it.  See:

Canadian Poisonous Plants Information System

Poisonous Plants of North Carolina

Plants Poisonous to Livestock:  Cornell University

However, I couldn't find clear evidence that living oleander plants release any sort of chemical into the soil to kill or inhibit the growth of other plants around it.  The only statement that I could find saying oleander is allelopathic was from The Lazy Gardener column that appears in several Marin County, California newspapers.  The author states that oleander is allelopathic and inhibits the growth other plants underneath it because it contains the compound called catechin.  Catechin is thought to be the compound that is the reponsible for the allelopathic effect of the invasive European Centaurea stoebe [synonym = Centaurea maculosa](spotted knapweed) against many North American native plants.

However, another paper [Gopinath, S. M. et al.  2011.  Chemical Prophylaxis and AntiBacterial Activity of methanolic and Aqueous Extracts of Some Medicinal Plants Against Bovine MastitisInternational Journal of Advanced Biological Research. 1(1) 2011:93-95.] did phytochemical analysis of extracts from several different plant species for a number of bioactive compounds (catechin being one of them).  Their results show that oleander leaves contain no catechin. 

 So, I suppose the bottom line is:

Probably the roots of the oleander do not exude an allelopathic compound; however, research has shown that extracts from the roots, stems and leaves do exhibit allelopathic effects when applied to some plants.  So, if the fallen leaves and stems are crushed and it rains or irrigation water falls on them, there may be enough allelopathic compounds leached from the crushed leaves or stems to affect plants in their immediate vicinity.



More Poisonous Plants Questions

What to do if Mexican buckeye seeds are eaten
September 09, 2011 - What to do if seeds of the Mexican buckeye are eaten? I didn't know they were toxic. Please let me know as soon as you can. Thank you
view the full question and answer

Does Virginia creeper cause a rash?
July 09, 2015 - Does Virginia creeper cause a rash to everyone or those who are only allergic as in an allergy like a peanut allergy? Is it something that should be avoided like poison ivy? And does the sap stick to ...
view the full question and answer

Will a barrier hedge of Agarita cause any problems for horses and cattle?
January 28, 2009 - Will planting a hedge of Agarita (Mahonia trifoliolata) at the fence line in my blackland prairie pasture cause any problems for my horses and cattle. I am trying to create a sound and sight barrier ...
view the full question and answer

Natural fibers for lashing bamboo in weaving
May 07, 2008 - I live in Austin and am looking for plants I can use for weaving fibers, e.g. lashing bamboo for a small project. What plants and parts do you recommend? What resources do you recommend for informatio...
view the full question and answer

Indoor and Outdoor, Fast Growing Plants for California
October 22, 2015 - Iím looking for the best plants for me. I have small kids so they would have to be safe. I would like them to be able to grow inside or outside. I would love for them to grow fast and reproduce fast.
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2016 Lady Bird Johnson Wildflower Center