Spring will soon be here and you will be out in the landscape solving plant problems once again. Insect and disease problems are often tough enough to diagnose, but problems not associated with a pest can be very challenging. These are called "abiotic" plant problems. An accurate diagnosis, whether biotic or abiotic, involves both science, (botany, entomology and pathology) and art (strategy, investigation and decision making). Abiotic problems can be very difficult to diagnose because they include site conditions, weather and cultural practices.
Unfortunately, by the time many customers notice that a tree or shrub is dying, it is already too late for a cure. That is why the recognition and prevention of adverse site conditions is very important. Woody plants, unlike herbaceous plants, are most severely affected by abiotic problems. Herbaceous plants tend to adapt better to adverse site conditions than woody plants. They also are less expensive, not as permanent, and easier to replace if they die than trees and shrubs. Some commonly encountered problems include:

Soil Grade Changes

Grade changes often are needed during building construction. Any changes to the original soil grade are usually very harmful to trees. Most experts agree that three inches of soil is the maximum depth that can be safely added without making special provisions such as tree wells. An indication of a fill problem is the lack of a flaring of the lower trunk. The tree will look much like a telephone pole. This leads to a slow death of a tree in two to five years.

Soil Compaction

This is a major problem after construction. Its effects will last for years before it gradually improves. Compacted soils have greatly reduced air spaces. They drain very poorly and plants usually die. Roots need oxygen in the soil. Soil compaction is a slow but sure process that causes poor growth and even death of mature, well-established woody plants. A soil analysis for nutrients, pH and bulk density can be very useful in starting a remedy plan for problem soils. Vertical mulching, radial trenching and tilling in organic matter are the remedy when possible.

Changes in Water Flow

Sometimes, correction of drainage problems elsewhere on a site diverts water to a tree or shrub, adding more water than it can handle. Another common problem is a downspout that does not drain away from a building because of excessive mulch or other obstructions. The resulting puddling damages plants. Sometimes, the damage does not appear until dry weather, when the plant is under drought stress. Take the time to observe the flow of water after a rain or irrigation. Look for leaking gutters and downspouts that do not empty far enough away from the building. In some cases, a total regrading of the site may be necessary.

Mechanical Root Damage

Most of the feeder roots of trees or shrubs are within the upper six inches of the soil. Digging, trenching, or roto-tilling within the root area of established trees or shrubs will cause harm. Root damage may haunt the plant months or even years later, depending on the environmental stresses that occur. A minor amount of damage may have no visible effect but severe damage will cause die-back.

Soluble Salt Damage to Roots

Root damage can occur from excessive fertilizer and misplaced ice-melt products. High applications of fertilizer or ice-melt products containing rock salt can burn roots, resulting in leaf scorch or death of the plant. A soluble salts test, if done as soon as possible before too much rain, will reveal the problem of over-fertilization or ice-melt product damage. Quickly irrigating with large amounts of water to flush the fertilizer salts is the course of action. Recovery may be successful, depending on the amount of roots killed by the salt.

Poor Soil Drainage

The efficient movement of water through the soil is critical to root health. Soil with good porosity, such as one rich in organic matter, is capable of handling large quantities of water with no harmful effects to plant roots. Most landscape soils are not this ideal and drainage during rainy weather is a challenge. Some popular landscape plants, such as white pines, azaleas, rhododendrons and yews, are very prone to root decay and become predisposed to fungal root diseases when grown in wet sites. Inspect the condition of the roots when digging out a dying plant. Dead roots are black or dark brown when scraped. Consistently wet soils will also have a foul odor caused by the anaerobic bacteria growing in it. A standard field test to check soil drainage is done by making a hole 18 inches deep and filling it with water. The water level should drop three inches every half hour.

Lower Trunk Damage

A number of things can cause trunk and stem damage. Bark can be damaged by frost cracking, excessive mulch, mowers, weed trimmers, and biotic causes such as rabbits, voles and other animals. Small amounts of damage can be tolerated but repeated damage that results in large masses of scar tissue is a serious problem. Damaged bark can not be repaired or reattached. The only remedy is to reduce the water stress on the tree or shrub by keeping it watered and giving it a fertilization in the spring or fall to increase growth.

Girdling Roots

Girdling roots may be a problem on shade trees, especially maples, zelkovas, elms and birches. Girdling roots take years to develop. Early detection is important. Young girdling roots that are visible on the surface and cutting into a tree trunk should be cut and removed. Removal of large girdling roots, over two inches, is a more involved process. It is best to seek the advice of a consulting arborist when considering their removal.

Planting Too Deeply

It is not uncommon to see trees planted three or more inches too deep. Deep planting causes bark deterioration at the soil line, which will eventually kill the plant. Various symptoms point to excessively deep planting. Some new growth may develop each spring, only to die-off during the stress of summer. Advanced symptoms of depth-related stress are cankers and deep cracking of the bark. Perform a root collar excavation. Carefully remove the soil from the circumference of the trunk to the point where the trunk flares out into rot growth. If the tree or shrub was recently planted, it can be lifted and replanted. To avoid excessive settling in future plantings, do not loosen the soil in the bottom of the planting hole. Planting trees and shrubs with the top of the root ball slightly above the existing soil line is recommended.

Excessive Mulch

Excessive mulching is a very common practice that leads to a gradual decline and even death of many trees and shrubs. Excessive mulch reduces soil oxygen for the roots. The roots, in their search for oxygen, grow into the mulch. During drought, the mulch dries out and the roots in the mulch die. When mulch is piled up against the trunks of trees and shrubs the bark decays and the entire plant may die. The ideal mulch depth is three inches, with none around the trunk.