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Saturday, January 12, 2013

Mesquite Does Not Normally Develop Extensive Shallow Roots

Pic of native mesquite I took in Jerez, Mex., showing sinker roots.
Q. I am a member of the Mesquite Club (est. 1911).  Our clubhouse is at 702 East St. Louis.  The patio concrete is fractured in many places and we are in the process of replacing it.  Inside the patio from St. Louis east side is a large mesquite tree (app. 50 yrs. Old).  The first concrete block is raised on the west side.  It has been suggested the tree is to blame and to remove it.  I spoke to concrete contractors and they felt the tree is not to blame. We have an underground stream in the St. Louis area that may have caused the problem.  The contractors, when removing the concrete, if roots are present, they will remove them.  A local nursery was contacted and said a mature mesquite tree’s root system would be the size of the tree’s canopy.  The tree is highly thought of and adds to our curb appeal.  Your advice would be appreciated. 
A. Nice to hear from you and from your historical club.  The roots of mesquite can be highly variable.  In the desert they have been traced down to over 150 feet in depth.  These are trees located close to a perennial rivers in the desert running through arroyos. 

Their root system is generally a three-tiered root system when grown naturally in the desert.  The first tier, or surface tier, utilizes water close to the surface after rains.  This is the easiest water for the mesquite to utilize and will expend very little energy to use it.  As this water disappears, deeper roots go to work in extracting water from greater depths where it still can be found. After extreme periods of drought, water may still be extracted from even greater depths. 

Dont remember the tree any more but not mesquite. surface roots.
When we grow mesquite in urban locations we seldom water them deeply.  Because of this, their roots tend to be a shallow and never develop their deep structure. 

It is possible the roots may be the problem but you will not know all until the cement is removed and the roots located.  Generally speaking I normally do not find tree roots to be a problem with lifting cement slabs or sidewalks if there is at least about 6 feet of open space between the tree and the concrete.  There are exceptions with mulberry being one of them due to its large number of surface roots. 

Desert trees normally don’t cause these problems but if the tree were watered with shallow irrigations and there was a lack of oxygen deeper in the soil, then the roots would tend to grow on the surface and be a problem.  I hope this helps. There are some possible alternatives that you might consider if you are keeping the tree.

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