Assisting Established Trees During The Hot Summer Months

Mark Arena,
Senior Extension Agent,
Cooperative Extension Service, Clemson University.

HTG 0717

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Water is the single most important ingredient for all living things, including trees in a landscape setting. Trees require water for photosynthesis, to deliver nutrients, to keep them upright, and for many other important functions. The relationship between a tree and water is an interesting one – too little or too much water will have a negative impact on the plant. All trees have a required range of water that satisfies their individual need. This individuality is where the challenge lies.

The one-year old arborvitae trees were not irrigated and are dying from the 2016 summer drought.
The one-year old arborvitae trees were not irrigated and are dying from the 2016 summer drought.
Mark Arena, ©2016 Clemson Extension

In South Carolina, the summer months present a stressful time of year for trees due to the unpredictable nature of the weather. Over the years, our state has witnessed a wide-range of weather conditions, from droughts to excessive rainfall during the summer months. These conditions are not favorable for trees and result in a reduction in vigor, growth, and appearance. Unfortunately, there is little one can do with excessive rainfall, except to try to improve drainage and run-off.

Drought also results in undue stress on trees. This stress causes them to become vulnerable to decline and poor performance, and potential insect and disease problems. Fortunately, drought, or the lack of adequate rainfall, is a condition that a homeowner can easily address. Simply watering the plants to counteract the water deficit is the first step. During the summer months, a tree should receive an average of one inch of rainfall or irrigation water every seven days. This recommendation should provide most trees ample water to survive and reduce the likelihood of stress.

Another helpful hint is to water the trees in the appropriate location. For trees, this means watering at the tree’s drip line. The drip line is located where the tree’s branches end. Watering one to two feet on either side of this imaginary line is the most beneficial location to deliver the water. To understand this idea better, the next time it rains, watch how the tree’s branching structure redirects the water to this area.

At times tree leaves may wilt during the heat of the day. Never water a tree just because its leaves are wilting. Wilted leaves are not always a sign that the tree needs watering. This condition may just be normal heat stress that the tree can manage. The best way to determine whether or not this appearance is due to heat stress or lack of water is simple. The following morning, go out and check the leaves to see if they are still wilting. If the plants are still wilting, water them. However, if the plants look normal do not water them and save the water for another day.

Watering trees in a landscape can be done manually or with the use of an automated irrigation system. Regardless of the system, the general goal is to delivery one-inch of water per week during the summer months. This includes any rain that may occur. One way to guarantee that an inch is delivered is to measure the water. This can be determined by using a rain gage, a can, or other object in which one inch of water can be measured. Once the water reaches the one-inch mark, stop watering. Then, keep track of the rainfall throughout the week and water as needed.

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.