There's a dirty little secret in our landscapes: Seemingly healthy trees and shrubs are experiencing preventable neglect and early death. Within 10 years of installation, specimens that once seemed to thrive suddenly develop diseases of the crown and other disorders, eventually failing. The average life span of trees in urban areas can be in the single digits, rather than in the decades or centuries typical to tree species.
Through research and practice, I have uncovered one problem that can go unnoticed at the time of planting: poor root structure (or inadequate root preparation). Roots grow normally until forced into an unnatural shape. Containers are often narrow and deep, not the best shape for the broad, relatively shallow root system of a tree. Nevertheless, roots will follow the shape forced upon them and unless freed from this arrange- ment will continue to grow as misshapen masses until they can no longer supply water or otherwise support the tree. This problem must be corrected during trans- planting; it is not enough to just remove the pot.
The city of Spokane, Washington, experienced heavy loss of new trees until 12 years ago, when it adopted the techniques described here. Since then, 97 percent of the trees planted have survived the hot, dry summers. Be forewarned: Many nurseries will not guarantee their plant materials if the customer disturbs the rootball. However, the benefits associated with preparing and correcting roots far outweigh the risks.
Correct problem roots before they become fatal. Potbound plants exhibit circling root systems that if not corrected become girdling roots, which can lead to the early death of otherwise healthy trees and shrubs. At transplant time, an aggressive approach to root preparation can uncover potentially fatal root flaws. Circling, J-hooked, knotted, and other misshapen roots can often be corrected by careful pruning.
Encourage the growth of new roots. Counterintuitive as it may seem, pruning induces new root growth. Once the plant is installed, new, flexible roots will begin growing immediately from tissue behind the cuts. These new roots, with their associated root hairs, are the absorbent roots and will begin to reestablish adequate water flow to the rest of the plant.
Remove materials that have no business in your landscape. Wire baskets, burlap, and twine all can interfere with normal root growth and slow or prevent establishment. There is no good reason to leave this material in a planting hole.
Promote the movement of air, water, and roots. The loose, soilless planting medium used to grow trees in containers provides too high a contrast with the denser soil surrounding the planting hole, deterring water (and therefore roots) from spreading beyond the hole. Remove as much of this planting mix as possible before the plant is installed. Similarly, when balled-and-burlapped trees are planted into the landscape, the differences between soil textures will inhibit root establishment. Removal of the soil in the rootball prevents this and also reduces the weight of the tree, making it easier to handle and install.
Trees Are Cool According to the USDA, the cooling effect of a healthy tree is equal to 10 room-size air-conditioners operating 20 hours a day. Planting trees in our cities will absorb 33 million tons of CO2 every year and save $4 billion in energy costs, says the National Wildlife Federation.
8 Steps to Healthier Trees
1. Using a hose or a water bath, remove all soil from the roots. Work out clumps of soil from between the roots using your fingers. Let rootballs soak for several hours if they are too dry to work.
2. Prune excessively long and defective roots. From this point on, roots must be kept submerged or wrapped in wet cloth.
3. Dig a shallow hole only as deep as the root system and at least twice as wide. In the center, form a soil mound to support the root crown.
4. Arrange the roots radially over the mound and backfill with the same soil that came out of the hole. Do not use any type of soil amendment.
5. Water well, using the water from Step 1, which will contain nutrients and microbes. Add more soil as holes develop, and gently firm the soil.
6. Mulch all disturbed soil with 4 inches of coarse organic mulch, keeping it a few inches away from the trunk. (Think "doughnut," not "volcano.")
7. Water your tree well during the first year of establishment. You have removed a good portion of the root system and its ability to take up water, and nutrients will be temporarily impaired.
8. Keep it simple and natural: Do not prune the top of the tree or add expensive but pointless transplant supplements.