When planting trees, it is best to back fill the hole with native soil because it encourages roots to grow out of the planting hole into adjacent soils. If there is a need ( based on soil tests) to amend the soil, it is important to incorporate amendments uniformly throughout the entire rooting area of the tree. Considering that the rooting area of a tree is more than twice the width of its canopy, it might be easier to select a species of tree better adapted to the site. Read more about soil amendments at this link.

backfilling