After planting a new tree, sometimes you will see decline, dieback, or even death of the young tree. When trying to determine the primary cause of the problem, several factors need to be given consideration. Remember that dieback does not always occur in the first year. Some factors contribute to poor vigor over several years or cause tree death two to five years (sometimes longer) after planting.
Underwatering is a common cause of death or decline in newly planted trees. Often the original root ball, where nearly all the roots for a newly planted tree are growing, will dry out sooner than the surrounding soil. Most newly planted trees will need supplemental irrigation during the growing season for at least two, often three or more years after planting. If water access is difficult, consider tree watering bags or other methods such as “leaky buckets” or drip hoses to provide water more easily when soil conditions are dry.
Poorly drained sites and/or overwatering will also cause a decline in tree health. Roots need oxygen and water-logged soils displace oxygen. How often newly planted trees need to be watered depends on soil type and drainage. The soil should be saturated when watering but allowed to dry out between waterings. Check trees frequently for adequate soil moisture checking both the original root ball and the surrounding soil. Only irrigate if either (or both) are dry.
Planting trees with the trunk flare below the soil line may cause mortality. The trunk flare is where the trunk meets the roots and is usually indicated by a change in bark color and a flaring out or swelling at the base of the trunk. Depending on the species, problems may occur when trees are planted only a few inches too deep. It is common for trees to be in containers too deeply and the top portion of soil in the container needs to be removed to reveal the trunk flare. Nearly all balled and burlapped trees will need soil pulled away from the top portion of the root ball to reveal the trunk flare. Planting holes dug too deep and filled back in with loosened soil may lead to the settling of trees, in effect causing planting that is too deep.
A planting hole dug only large enough to insert the tree's root system can lead to problems, especially if the soil is very compacted or high in clay content. These circumstances make it difficult for the new roots to penetrate the existing soil and grow. The planting hole should be wide to give the newly planted tree a better chance of growing out of the original root ball and into the surrounding native soil.
Quality of Stock
A tree that shows good branch and foliage growth is not a guarantee that the tree will thrive. It is important to consider the root system. Examine the roots before planting. An abnormally high shoot-to-root ratio (extensive root loss) may lead to failure. Roots that are allowed to dry out before planting may die. If an excessive number of roots are circling the root ball, they will likely continue to grow in their circular direction rather than out into the native soil.
Environmental extremes, such as abnormally low winter temperatures or late frosts, can kill plant tissue causing dead branches or sections in the tree. Warm winter sunlight can also dehydrate tender tissue or cause sunscald on thin bark. This damage weakens the tree making it more susceptible to other issues.
Insect or Disease Issues
Newly planted trees are under more stress making them more vulnerable to insect pests or disease issues that the tree would normally be able to ward off if it was more established and growing more vigorously. In most cases, any insect or disease issue is secondary to another problem like overwatering or improper planting. Addressing the pest or disease may eliminate the problem on the surface, but it does not address the underlying issue that allowed the insect or fungus to become a problem in the first place.
Other factors can contribute to poor establishment and mortality of newly transplanted trees.
- Girdling wires from tree supports can cut off vascular tissue and the movement of water and nutrients from roots to leaves.
- Piling mulch too deeply at the base of the tree and burying the trunk flare creates issues similar to those when the tree is planted too deeply.
- Poor soil pH can make some nutrients, like iron, unavailable, causing chlorosis or dieback.
- Improper species selection may lead to tree decline. Planting a species not well suited to the site's environmental conditions (such as heavy, wet soils) leads to decline. If a species more tolerant of the site conditions was planted instead, fewer issues would exist.
- Chemical injury from improperly applied herbicides in nearby gardens or fields or pesticides, fungicides, or other chemicals not applied as directed on the label or applied in improper weather conditions, such as too windy or hot, can lead to damage.
- Mechanical damage such as scrapes and broken branches during transportation; gashes, scrapes, or cuts during planting; or damage from mowers, string trimmers, or other maintenance equipment can damage vascular tissue or open trees to insect or disease issues.
In many cases, several factors may be contributing to tree mortality. Pinpointing the primary factors will allow you to take corrective measures in future plantings.