Planter's around trees

Adding soil around the trunk of a tree will more than likely cause the bark layer to rot which will eventually lead to the decline and death of the tree.

Adding soil around the root system of a tree will also cause the tree to decline because the air exchange has been disrupted.

In both cases it might take 5 years or more to see the full effect of the damage.

Dennis - Johnson County Extension

We are not sure what you mean by a planter box built around your tree, but raising the dirt any amount above where it is currently can kill your tree. A foot of dirt would most certainly kill it. The other thing about planting around trees is that the plants will have considerable competition from the tree for moisture & nutrients.

Lynn
Johnson Co Extension Master Gardener