In October I was asked to visit a property in Jacksonville to determine the cause of the declining live oak that had been planted by a nursery in March, seven months earlier. The tree was experiencing drought stress indicated by a extremely dry rootball and dieback in the crown in spite of a summer of abundant rainfall and regular irrigation.
I performed a root crown excavation with a hand hoe and soon discovered the tree had been planted too deep while in the nursery, had an impermeable weed mat on top of the rootball and had circling roots that prevented any root growth out into the surrounding landscape.
Planting too deep and an impermeable weed mat:
I found a layer of very dense fibrous roots on top of the rootball. This dense layer of organic matter varied from 1 inch to 3 inches thick and extended over the entire top of the root ball from the base of the trunk out to the edge of the rootball. This layer of organic matter was very difficult to remove and had the consistency of coir material made from coconut husk fibers. Although I was not sure a coir weed mat disk had been used on top of the rootball, the consistency and thickness of the fibers was very similar to that of a coir weed mat. Fibrous adventitious roots had grown into the mat making it impermeable to all but the most prolonged soaking.
The tree had been left much too long in its undersized container in the nursery causing the roots to circle the container once they grew out the the edge of the rootball. Not only will the tree fail to develop fully, it will become very unstable in wind storms and could easily fall over once the crown becomes larger. The nursery must have had complaints about the instability of its trees because they drove a heavy pipe through the rootball into the soil below to anchor the tree in place. This pipe is a very short-term, band-aide method of creating some stability until the warranty period is over. The pipe does not fix the circling root defect in any way.
Cutting circling roots:
The circling roots must be cut at a point before they turn and begin to circle. Some roots do not circle but grow down to the bottom of the pot and then grow upward to the top of the soil on the other side of the rootball. Once near the soil surface these “diving roots” will often grow back toward the trunk becoming stem girdling roots.
The final treated rootball is much smaller than the original. This process is stressful for the tree and irrigation must be applied regularly (daily at first in warm climates) for weeks and even months for larger trees. (For a University of Florida article by Dr. Ed Gilman on proper watering for establishment, go to: http://edis.ifas.ufl.edu/ep113.) The end results looks scarey but this is the only way to give the transplant tree a future of maturing to its full natural size and providing the many benefits we expect from healthy trees.