Preparing the planting site

Improper site preparation is a common reason trees and shrubs don't grow after planting. It is a particularly big problem in areas where the soil is a heavy clay type. Such soils have poor drainage and lack a sufficient amount of air to allow vigorous root growth.
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 2 to 4 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. In extreme cases, 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. Putting pea gravel in the bottom of the hole does NOT improve drainage.

The economic pressures in landscape installation these days often cause crews to “shoe-horn” the trees and shrubs into holes barely big enough to accommodate their root ball. This may save time at planting, but you will pay for it later with replacements and customer dissatisfaction.