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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.

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Monday - March 11, 2013

From: Washington, MO
Region: Midwest
Topic: Erosion Control, Trees
Title: Further explanation of retaining walls and trees from Washington MO
Answered by: Barbara Medford


I had a question previously about putting retaining walls across the root system of a 40' tall bald cypress tree(not like spokes on a wheel, but concentric to tree trunk). How wide can the walls be? How deep can the dirt backfill behind the walls be? How far away from the trunk should the walls stay? I am only asking how to minimize stress to the tree, not how to engineer it. My choice of words gave you the wrong direction to proceed with your answer. Please address only the plant/tree issue for me.


Sorry we got so wrapped up in the rain garden issue we forgot the tree root issue. In fact, we had a reference to tree wells in our original answer and removed it because the answer got so long. For anyone interested in seeing how we goofed up, here is your previous Mr. Smarty Plants question.

Basically what you are asking about is Tree Wells. This article, we believe, actually addresses the questions you have, and much better than this mathematics-challenged gardener could. It has diagrams, a discussion of grade changes, the distance a wall  should be from a tree trunk, weep holes, etc. Since you can actually see your tree, the incline and soil type, hopefully this will answer all the questions we did not.


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