Dangers of Root Disturbance

DANGERS OF ROOT DISTURBANCE

All trees are sensitive to root disturbance. Examples include construction, over watering, sprinkler instillation, and grade changes. The effects of these changes on pre-existing trees can take five to ten years to become fully visible.

To understand how trees are affected by root disturbance, it is important to understand the structure of a tree’s root system. Ninety percent of the root system is located in the first eighteen to twenty-four inches of soil, and the roots extend radially from the trunk one to two times the height of the tree.

During construction, the root system is cut to install foundations, sidewalks, driveways, and landscape beds. The closer to the tree the construction occurs, the more destructive it is. Damage also occurs through compaction of the soil from heavy equipment repeatedly driving over the root zone. Clay soils compact more easily than sandy soils. Compaction of the soil reduces the pore space between soil particles, eliminating the oxygen in the soil, causing root decay. Further damage results from utility lines and irrigation systems being installed. Sprinkler instillation can cause just as much damage as initial construction due to the amount of trenching in the root zone.

Watering the new landscape can then cause even more damage. Most of our native trees are adapted to dry sites and are used to receiving natural rainfall (30” of rain a year). When an increase in water occurs, the soil can stay saturated, eliminating the amount of oxygen. Roots then begin to rot in this anaerobic condition, and the tree begins to decline or die. Clay soils stay saturated longer than sandier soils.

It is recommended to limit watering to 1” of water a week during the growing season including rainfall. This will allow the soil to be moistened and dry out, mimicking this region’s natural rainfall pattern.

Remember slope, drainage, natural rainfall, and sun exposure will vary the frequency and duration of the sprinkler system schedule.

Improvement of the soil through fertilization is recommended to encourage new root growth. Fertilizing three to four times a year for the first few years following root damage is common. Root regeneration can take many years, do not expect quick results.

A systemic insecticide can be added to the spring fertilizer application to reduce insect feeding. Borers commonly attack stressed trees causing significant and irreversible damage. Active damage can be recognized as weeping fluid or sawdust on the trunk, but it is not always visible. Systemic insecticides cannot be applied to fruit trees such as Pecans, Walnuts or Peaches.

Because trees are stressed following construction, pruning should be minimal the first few years. The more leaves and branches in the tree, the more food the tree can produce aiding in recovery. Branches causing clearance problems with houses, driveways, or streets can be pruned.

When trenching to install a sprinkler system, stay as far from the trunks as possible, preferably outside of the canopy drip line. Commonly a combination of rotary heads along the perimeter of the yard and popup heads in the landscaping beds works well. If trenches must be dug under the tree’s canopy, try trenching radially towards the trunk instead of across the root zone.

EXAMPLE OF IRRIGATION INSTALLATION

February 2008