Q. What is the advantage of planting large box trees versus planting a tree in a 15-gallon container, other than size? Some of the box trees planted along our street don’t seem to be very healthy. Many look half dead (literally-one half of the tree appears dead while the other half has leaves).
For those people who want instant shade and a mature-looking landscape, a box tree can be an option, albeit an expensive one. They are difficult to plant, usually requiring specialized equipment. The hole must be just deep enough to contain the roots, but not so deep as to bury the root crown. If the ground settles enough to bring the crown below ground level, the tree can succumb to crown rot.
Larger container-grown trees tend to suffer from circling roots. As the tree grows, the roots grow outward until they reach the inside surface of the container. Then they begin to grow circularly and continue to encircle the root ball. Once the roots start circling, they will continue to do so even after planting. If the tree is still young and the roots still flexible, they might be redirected to grow outward, but this usually requires some root pruning.
For example, we purchased a 15-gallon Asian pear tree and planted it in our garden. For years, it stayed the same size. It still put out leaves but never flowered and never grew. We finally dug it out and discovered that the root ball on this 7-foot-tall tree was about the size of a one- gallon pot. The roots were hopelessly knotted into what looked like a tight fist. Needless to say, it wasn’t difficult to dig it out. We may have had better luck if we had knocked the dirt off the roots and disentangled the roots before putting it into the ground.
For this reason, trees that have been transplanted from large containers or boxes will generally not fare well in strong wind conditions.
The half-dead trees you see are most certainly suffering from a girdling root. When a tree has circling roots and is planted, the trunk may grow thicker, but the circling root is also growing. Once the root and trunk come in contact, the root will press against the trunk, cutting off circulation to that side of the tree. That is what causes half of the tree to die.
Palm trees are an exception since, due to their fibrous root structure, they will transplant from a box or large container very readily.