The University of Arizona Plant Sciences Department has released new recommended Planting Standards to improve the viability of new trees when transplanted in our Arizona soils. These planting standards are a compilation of research studies of other Universities, American Forests, International Society of Arboriculture, and independent research of leading national Horticulturists with modifications for Arizona Soils and climates.

1. Planting hole should be three to five times the diameter of the root ball and no deeper. The sides of the hole should be rough or sloping. Trees develop a root system that extends one and a half to four times the canopy diameter and lies within two feet of the soil surface. This lateral root system supports the tree and absorbs water and nutrients. Transplanting practices should encourage root spread.

2. Set the top of the root ball at or slightly above the soil surface. Trees planted in holes deeper than the root ball tend to subside as irrigation compacts the soil beneath the root ball.

3. Remove the tree from the container. Avoid lifting the tree by its trunk. Disentangle and spread any roots that had circled in the container. Score the sides of the root ball to encourage lateral root growth.

4. Place the tree in the hole and backfill. Do not add amendments to the soil. Do not tamp with your feet. Form irrigation borders (if used) just outside the root ball. Amended back fills tend to restrict root spread and reduce top growth. Amended back fills also tend to wick water away from the root ball.

5. Spread mulch on the soil surface to a depth of three to four inches. Keep mulch away from the tree trunk.

6. Do not prune unnecessarily. Root initiation and growth is stimulated by stem buds and leaves. Therefore shoot pruning reduces root growth and prolongs establishment.