Why Adding Soil Around Tree Trunks Kills Trees

Covering the base of mature oaks with 2 feet of topsoil will almost certainly kill them. Tree roots require oxygen, and 95% of feeder roots reside in the top 12 inches of soil. Burial suffocates roots, disrupts gas exchange, and initiates a slow decline—sparser foliage, dieback, and eventual death over several years.

The Science of Root Respiration

Roots need oxygen for respiration. Soil pore spaces provide this. Adding fill soil compacts the existing soil and reduces oxygen diffusion. The tree cannot grow new roots upward fast enough, especially mature specimens.

Alternatives for Leveling a Yard

Consult a landscape professional experienced in tree preservation. Techniques include:

• Grading away from the trunk in a gentle slope.
• Using a retaining wall to hold back fill at the tree's dripline.
• Installing a tree well with aeration pipes (though success varies).
• Accepting the natural grade and designing around it.

Immediate Action

If fill has already been added, remove it immediately down to the original grade. Monitor the trees for stress and provide supplemental water during dry periods.