I was wanting to put a raised
flower bed around a very large pecan
tree in my front yard. I found the following from the FAQ page of Oklahoma Gardening
"Question #2: My husband wants to build a
flower bed around a river birch, with 3 branches, that is 8 years old. What precautions should we take when building the bed to keep from doing any damage to the
tree. The bed will be 14 inches deep. This
tree has a lot of sentimental value tome and I don't want to lose it. Thank you for any help you can provide.
Answer: I would strongly recommend against building any bed under an existing
tree like that, especially if there is sentimental value. Drastic grade changes such as the one you are proposing are often detrimental to a
tree. Roots
growing near the surface are responsible for oxygen uptake. By burying them 14 inches you are basically suffocating the roots which often results in death. For further information refer to our fact sheet F-6429 - Site Disturbance and
tree Decline. A copy can be obtained from your county extension office or by going on-line at http://agweb.okstate.edu/pearl/hort/ornamental/index.html"
It made me change my mind.
Copperdog