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 - 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

QUESTION:

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

ANSWER:

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

Are palm leaves poisonous?
August 18, 2008 - Are palm tree leaves poisionous? Because my dad was doing yard work and was stuck by a palm tree leaf in his calf. His calf has swollen and in he thinks it broke off in his calf.
view the full question and answer

North American Plants with Poisonous Thorns
December 01, 2011 - Are there any plants in North America that possess poisonous thorns?
view the full question and answer

Could hickory leaves be used as seasoning from Waynesboro VA
September 17, 2011 - I have a hickory tree. If I pull a leaf off and rip it then smell, there is a strong wonderful scent of hickory much like when I rip a mint leaf there is a strong smell of mint. So my question is, can...
view the full question and answer

Is Texas Mountain Laurel Honey Toxic in Fulshear, TX?
March 11, 2012 - Toxicity of Texas Mountain Laurel HONEY I know the seeds and leaves of the Tx Mountain Laurel are toxic. But, is honey that comes from the Mountain Laurel toxic too? I heard that it is, but can'...
view the full question and answer

Is Desert willow poisonous to horses in Boerne TX
July 17, 2009 - I have just purchased Bubba Desert Willows and have horses. Will they eat them, do you know and if so will they be harmed? Thanks
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