Part 1: Oxygen
Good tree root health
In our urban and suburban forest we are challenged to help our trees to overcome the handicaps of living in the built environment. Most of the problems that affect tree health are found underground. We know this to be true because of all of the research that has been done regarding tree health in the built environment. Sadly, very little effort is put into the root zone of trees, though. And what little effort is made in urban arboriculture is not very helpful to root health.
You may have already spoken to an arborist about improving the root health of your trees. Unfortunately, the response from plant health care professionals is likely to be fertilization. In the vast majority of cases involving declining root health, the problem has nothing to do with fertilization. The problem with urban tree roots is usually respiration.
It is not often talked about, but tree roots must respire to survive. In the tips of the roots where absorption takes place oxygen is critical to root life. If oxygen levels drop too low, then roots will die. It is this low oxygen level that is more likely to be the cause of declining root health than any nutrient deficiency.
The reasons for oxygen deficiency can be:
If the soil supporting tree roots is saturated beyond field capacity and fails to drain, then the soil will become anaerobic and suffocate the roots of trees. By contrast, good drainage draws oxygen into the soil. As the water leaves the macro pores of the soil, air is drawn in.
Heavy traffic (pedestrian or vehicular), construction, plow lines, and even the weight of constant surface irrigation can compact soils to the point that they will no longer support the oxygen levels needed for root growth. Compacted soil can be irrigated every day and still not ever support tree roots.
Rises in soil temperature can drastically increase the demand by aerobic organisms within the soil for oxygen. This competition can lead to depleted levels and poor tree health.
There are corrective measures that can be employed as mitigation for all of the contributing factors to oxygen deficiency in soil. For drainage issues, trenching in drain pipe may be the answer. For soil compaction, air spading and structuring, or simply installing rootwells can achieve the necessary levels at depth. When there is too much competition from microbes, a more stable organic matter can reduce the level of soil composting.
An arborist can help to solve the problem, but beware of one who pushes the idea of "deep root fertilization" as this is not going to do anything to deliver oxygen. Of the things that are necessary for root activity, oxygen is the most important to the trees that we care for.
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More About Soil Remediation
Good Tree Root Health: Oxygen. In the tips of the roots where absorption takes place, oxygen is critical to root life.
Good Tree Root Health and Microbes. The forest floor provides an ideal environment for their propagation, and they are constantly cycling through the soil food web. In contrast, urban and suburban soil can be seriously lacking in these microbes.
Root Aeration Tubes There are numerous options for root aeration tubes. A popular design involves PVC plastic pipes.
Rootwell Products The Rootwell Products, direct-to-root system has been engineered to permanently enhance a tree's natural ability to absorb oxygen, water, and nutrients.
Soil Compaction In the built environment where most of us live, soil compaction is a necessity.
Soil Composition When we consider the make-up of soil we are looking at the percentages of three different components, sand, clay, and silt.
Soil Food Web What horticulturists and soil scientists refer to as the soil food web is an intricate network of life forms.
Soil Structure Soil structure essentially refers to the amount of macropores in the soil.
Tree Root Health: Watering Trees. What we see in lawns that are irrigated conventionally is tree roots growing at or near the surface in the only space that they can live.
Trees Suffering From Drought? Take a walk in an established forest in this area, and you will see that the problem is not really the drought.
Water Is Not Enough This tree is watered daily by an automatic irrigation system. Despite the abundance of water, it is stressed and losing leaves in July.
Why is That Tree Not Growing? Why is it that the trees in some landscapes never seem to grow past the half-way point of their mature size?