To reduce these problems when planting trees and shrubs, measure the width and height of the root ball of a tree or shrub to be planted. If the soil is sandy and drains well, dig the hole the same depth as the root ball. If the soil is heavy clay and drainage cannot be improved, dig the hole twice as wide or wider as the diameter of the root ball. The depth of the hole should be two to four inches more shallow than the height of the root ball. This ensures that the top of the ball is slightly elevated from ground level so excess water will drain away from the trunk of the tree.
Tree roots grow far beyond the original planting hole.
Soil that is not compacted encourages root growth. Loosening ordinary soil with a shovel beyond the tree will help the roots develop. Adding about one part coarse organic materials to two parts soil is also helpful. Do not mix in commercial fertilizers or fresh manure. They can damage new roots.