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 Problem Plants Questions

Controlling Passionflora Incarnata propagation
March 20, 2012 - Would a cinderblock raised bed, 8 inches in height, be sufficient to contain the roots of passiflora incarnata and keep them from traveling to places where I don't want the vine? Are the roots deepe...
view the full question and answer

Skin allergies; is Juniper the culprit in Simi Valley, CA?
July 21, 2012 - My husband and I have had terrible skin allergy problems this spring (for me it's been 3 years) and think it may be the juniper bushes outside our bedroom and kitchen windows. Is there a fast growin...
view the full question and answer

Eliminating evasive Celastrus orbiculatus (Oriental bittersweet)
July 21, 2013 - I have Oriental Bittersweet growing pervasively in my shrub garden, strangling my shrubs and growing into my beautiful Victorian porch. I can't keep up with it! What can I do?
view the full question and answer

Invasive thistles in wildflower field from Dripping Springs TX
February 17, 2014 - How to get rid of "native" thistles.. I have a large natural field that used to grow a variety of wildflowers, but in 2011 and 2012 it was taken over by thistles. I'm sure they are "native" Texas...
view the full question and answer

Germination of Sophora seeds, and Dodder identification in Kingsland, TX.
May 02, 2012 - Our Mt. Laurel has just produced seeds. Can those be scarified and planted now or do they have to dry out. Also what is the stringy orange substance that gets on bluebonnets and other wildflowers ...
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 | STAFF
© 2015 Lady Bird Johnson Wildflower Center