Here is the City of Portland’s Street Tree Planting and Establishment brochure.
Bare Root Seedlings – Keep the tree’s roots moist until the tree is planted. The hole should be as deep as the longest root and twice as wide as the root cluster. Create a small mound of soil at the base of the hole, place the roots on the mound, and gently add soil back into the hole, avoiding air pockets and compacted soil. Water the tree after planting.
Balled and Burlapped (B&B) Trees – Dig a hole twice the width and equal in depth to the root ball. Remove any wires or burlap. Place the tree in the middle of the hole and stabilize the tree with back fill. Add the rest of the soil back in the hole, avoiding air pockets and soil compaction. Water the tree after planting.
Containerized Trees – Dig a hole as deep as the container and twice as wide. Remove the container and gently tickle the roots to loosen them from the soil. If any roots are circling, slice the circling roots with a knife. Place the tree roots gently in the hole and back fill. Avoid air pockets and soil compaction. Water the tree after planting.
** Tree care content from Friends of Trees.