Root barrier

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A root barrier is an underground wall placed to block plant roots. This is often for the purpose of protecting structures or other plants, but root barriers are also used to preserve soil moisture.


Root barriers were developed to stop trees damaging buildings. Concrete was historically a common material but since 1992 plastic root barriers have become more common due to their resistance to cracking caused by soil and moisture movement.


Root barriers intended to protect structures normally run parallel to the structure at a distance. They typically extend down to a naturally-occurring soil layer which is not penetrable by roots, to prevent the roots growing under the barrier. To avoid endangering trees, root barriers must be placed some distance away from the tree and avoid surrounding it completely.


Root barriers can be used to protect infrastructure from damage by tree roots below.[1] They are also moisture-proof, which can be useful to preserve buildings on clay soils by preventing moisture escaping laterally.[2] After installation the soil under the building can be rehydrated if necessary.

Root barriers are also used to separate plant roots from each other. In particular, walnut trees secrete the chemical juglone which is toxic to other plants but the use of root barriers can prevent the yield reduction that would normally occur when walnut trees are alley cropped with maize as often occurs in the American Midwest.[3][4]


  1. ^ Application of a new vertical moisture barrier construction method for highway pavements, R. P. Evans, J. C. Holden and J. K. McManus. Published Vol 5, No3, September 1996 Road and Transport Research
  2. ^ Expansive Clay soils and Vegetative influence on shallow foundations, ASCE Geotechnical special publication number 115
  3. ^ "Airspade". Retrieved 22 January 2017.
  4. ^ "Allelopathy in black walnut (Juglans nigra L.) alley cropping. I. Spatio-temporal variation in soil juglone in a black walnut-corn (Zea mays L.) alley cropping system in the midwestern USA (PDF Download Available)". ResearchGate. Retrieved 2017-04-20.