Article 4 of 12 from Trees: Dispelling Myths & Misinformation, prepared by the arborists of the Southwest Division of Bartlett Tree Experts as a community education initiative.
One morning, a friend found his 15-foot-tall cedar elm uprooted and flat on the ground. What a waste! It had been planted about five years earlier and was about to really take off. An investigation of the root system revealed three things: The soil line was a few inches above the trunk flare, girdling roots were present at the base, and about half of the root system appeared underdeveloped. This tree was doomed from the start, in part, because of a poor planting job.
We won’t address all of the steps of tree planting; you can find those at treesaregood.org, an excellent resource for consumers. Our aim is to call your attention to a few avoidable mistakes that too often sabotage a tree’s survival.
The first thing to be aware of when purchasing a nursery tree, commonly sold in a container, is how it was handled at the grower. As the little tree outgrows its container, it’s placed in the next bigger size, and so on until it’s ready for sale to the retailer. Often, the tree is held in a pot too long, and the roots begin to circle inside the container, continuing that growth pattern into the next-size pot. Unless circling roots are addressed at planting, they can eventually girdle the tree.
Picture a major root circling the stem (trunk). Now picture what happens when both grow bigger. The root’s chokehold on all or part of the stem can restrict movement of water and nutrients and eventually kill the tree. This condition can also make the tree unstable. So when planting the new tree, loosening and spreading out the roots are essential. If some circling roots have become woody, they may need to be cut (not torn).
Going back to our grower pots, as soil is added to each larger pot, it’s possible that soil will cover part of the lower stem, and roots may grow up into it. This encourages the tendency to plant the tree too deep. Locating where the roots begin to spread at the stem base (the root flare or what will become the root crown) will help determine how deep to plant the tree because, as we learned in the last article, the root flare should not be buried.
A narrow planting hole will encourage root circling and inhibit good establishment, especially if the soil is compacted, as is common in urban soils. A hole three to five times the diameter of the root ball will allow the roots to expand properly and become better established. Since roots begin establishment within the top foot of soil, planting too deep will deprive roots of adequate oxygen. Positioning the root flare slightly above the soil line will encourage better root health, and, again, it will keep moisture away from the root flare.
In the next article, we’ll look at a few aftercare practices that influence a newly planted tree’s chances for survival.