Dr. Wayne Porter is a regional extension specialist of horticulture with the Mississippi State University Extension Service in Meridian.

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Abiotic Disorders in the Landscape
by Wayne Porter       #Trees

Circling roots can eventually girdle the trunk or other roots of this Chinese elm (Ulmus parvifolia). Small roots like these can be safely removed.


Plants are often subjected to stresses in the environment that are not results of insects or diseases. These stresses are referred to as “abiotic” diseases. These abiotic disorders result in the plant being less vigorous and in many cases dying. The majority of these stress situations are the result of human activities.

Abiotic problems often involve multiple factors. A plant’s response to these factors can be subtle in nature and accumulate over time making them difficult to diagnose. It can be even harder explaining to a homeowner how they harmed their plant by something they did years ago.

Typical symptoms of abiotic problems include very slow growth, poor foliage color, leaf scorching, the presence of lichen, limb dieback, or plant death. Following is a discussion of some of the more common abiotic problems that occur in the landscape


This live oak (Quercus virginiana) died because it was planted too deep.


 

Proper Tree Planting

•  Determine where the root flare is located.
•  Dig the planting hole two to three times wider than the root ball, but no deeper.
•  Gently place the tree in the planting hole with root flare at or slightly above grade.
•  Backfill planting hole with excavated soil and water to eliminate air pockets.
•  Apply 2-4 inches of organic mulch. Keep away from trunk.
•  Stake only if necessary with wide webbing. Tree must be able to move in the wind.
•  Water throughout growing season with 1 inch per week.
•  Remove stakes and ties within one year.

Planting Too Deep
One of the most common and serious problems associated with tree planting is planting too deep. Many trees and shrubs are set too deep at the time of planting, or they settle over time. A planting depth of only 1 inch too deep can cause eventual problems. It is not uncommon to see trees planted as much as 3 or more inches too deep. If a tree looks like a telephone pole going into the ground, then it is planted too deep.

Various symptoms point to excessively deep planting. New growth may develop each spring, but dieback of branch tips occurs during the stress of summer. Advanced symptoms of depth-related stress are cankers and deep cracking of the bark.

Making sure the root flare of a tree is at or slightly above grade when a tree is planted easily prevents this problem. (See tree planting sidebar)


This tree suffered damage when a string-trimmer was used to cut basal watersprouts.


Mechanical Damage
Mechanical damage leaves tree and shrubs vulnerable to disease organisms. Damage comes from vehicles, string trimmers, lawn mowers, construction equipment, garden tools, animals, or other human activities. String-trimmer injury is particularly harmful for trees and shrubs with thin bark. Repeatedly bumping into the same area of a trunk without cutting the bark can damage or kill the growing point under the bark and result in reduced growth. Creating a machine-free zone around trees and shrubs with mulch will greatly reduce mechanical injury.


Improper Mulching
Mulch is used around plants to help conserve soil moisture, moderate soil temperature, reduce weeds, and keep equipment away from plant trunks. The recommended depth is 2-3 inches for most organic mulches. Many gardeners, believing more is better create mulch “volcanoes.” When mulch is piled up against the trunks of trees and shrubs, the bark stays too wet and decay can occur and the entire plant may die. Keep mulch several inches away from the trunk to prevent this scenario.


Mulch “volcanoes” create an ideal environment for disease organisms. Keep mulch 2-3 inches away from the trunk.


Girdling Roots
A girdling root is a root that circles around the trunk or other roots at or below the soil line, gradually cutting off the flow of nutrients. Some trees, such as maples, elms, and birches, are particularly prone to their formation. Trees and shrubs that are container grown and have become pot-bound frequently develop girdling roots. It is important to spread or cut circling roots at planting time to prevent future problems.


Mechanical Root Damage
Most of the feeder roots of trees or shrubs are within the upper 6 inches of the soil. Any digging, trenching or roto-tilling within the root area of established trees or shrubs will cause harm. Damage usually occurs when establishing a new flowerbed, planting shrubs under trees, installing a sprinkler system, or paving a driveway or patio area. The degree of damage depends on the depth of the digging and the amount of ground covered. Root damage may haunt the plant months or even years later, depending on the environmental stresses that occur after the damage.


This huge live oak is showing dieback of branches due construction damage that cut feeder roots.


Construction Damage
Construction damage impacts trees and shrubs in numerous ways. There is severe root loss or injury, compacted soils, loss of leaf area, and grade changes. The impact on trees can be short term, but it usually sets the tree up for a gradual decline or death that takes several years. Anytime the soil grade is lowered or raised even a few inches, existing shrubs and trees become predisposed to various stresses. Keep construction equipment and building materials outside the drip line of trees.

Humans unknowingly inflict these abiotic stresses on trees and shrubs in the landscape. It is amazing how forgiving plants can be, considering all the pressures we humans put on them. Only further education about landscape maintenance will reduce these human-caused disorders.

 

A version of this article appeared in a January/February 2014 print edition of State-by-State Gardening.
Photography courtesy of Wayne Porter and istockphoto.com/eurobanks.

 

Posted: 04/19/17   RSS | Print

 

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