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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.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - May 06, 2009

From: San Antonio, TX
Region: Southwest
Topic: Non-Natives, Diseases and Disorders, Trees
Title: Will Mountain Laurels be harmed by juglones from my pecan tree?
Answered by: Jimmy Mills

QUESTION:

Hi. I just bought a house. It has a big pecan tree at the edge of the front lawn next to the street. I guess it's about 25 feet from the front of the house. I was thinking of planting mountain laurels near my front windows, pretty far from the pecans, but I read on another forum that mountain laurels will not grow within 50 feet of a walnut tree. Doesn't the pecan have the same toxin as the walnut, and so would it be a bad idea to try mountain laurels in my spot? If not, what about loquats?

ANSWER:

The pecan Carya illinoinensis (pecan) is a member of the family Juglandaceae which contains the Hickories and Walnuts. Members of the family produce the chemcal juglone that is allelopathic  to some plants but not others. One role of the toxin is to prevent the growth of competing plants under the tree. It appears that the level of  juglone in pecans is less than in walnuts. 

You can see lists of plants susceptible to juglones and those tolerant of juglones from Michigan State University and Ohio State Univeristy. Mountain Laurel Kalmia latifolia (mountain laurel) appears on the susceptible list, but this is probably not the Mountain Laurel you have in mind (it doesn't usually grow in Texas). In San Antonio, Mr. Smarty Plants suspects that you want to plant Sophora secundiflora (Texas mountain-laurel) which is not on the susceptiple list, and would be a great addition to your front yard.

As for loquats; since the mission of the Ladybird Johnson Wildflower Center is to increase the sustainable use and conservation of native wildflowers, plants and landscapes, Mr Smarty Plants would prefer that you not plant loquats which have been introduced from Southeastern Asia.


Carya illinoinensis

Sophora secundiflora

Kalmia latifolia

 

 

 

 

 

 

 

 

 

 

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