If the planting site is appropriate for the tree, there's no need to amend the soil more than 10 percent. It's better not to create an artificial root zone by over-enriching the soil in a limited area. Eventually, the roots will have to grow beyond this rich zone where they are cozy, and they may have trouble adjusting to the poorer, surrounding soil. If the soil simply isn't suitable for this tree, I amend it to accommodate the mature tree's root span.

I favor composted cow manure to amend any type of soil, but other organic compost will do. They provide many essential nutrients and mycorrhizae, which help the roots to absorb nutrients. I never use peat moss as a soil amendment; it acts like a sponge and then hardens when it dries, thus constricting the roots. Before backfilling, I mix the compost into the soil in a 1-to-10 ratio.

After placing soil around the bottom of the planting hole to steady the tree, I stand back and check from all sides to make sure it is straight. I also check the planting depth one last time (above right). As I backfill, I tamp inside the hole, add another 4 to 5 inches of soil, and tamp again continuing until the hole is full. I never let sod, large rocks, or construction debris get backfilled, since they can interfere with root development.