Are Your Trees Suffering in the Summer Heat? Here’s How to Tell Before It’s Too Late

During the spring and summer, everything looks so glorious when it’s bright and colorful. Fertile grass, a blooming garden, tall green trees: It’s a wonder of nature to see everything so alive and lush…until it’s not. The heat of summer can really wreak havoc on plants of all kinds, particularly when there are drought-like conditions.

According to The Old Farmer’s Almanac, most of the country is due for another scorching summer. And while most people see the warning signs of stress on lawns and gardens, did you know that your trees can also suffer in prolonged heat? They may be more subtle, but there are signs of tree heat stress to look out for. If ignored, the trees may not survive! Given how special they are, it’s best to keep an eye on them so that doesn’t happen.

Thankfully, you’ll find some expert advice right here from W. Jim Cortese, an arborist, forestry consultant, and natural history storyteller based in Knoxville, Tennessee. With more than forty years of experience in arboriculture and urban forestry, he’s here to help you identify the subtle signs of heat stress in trees and what to do to help save them and keep them healthy for years to come.

signs heat stress in trees

Ferenc Oláh – Getty Images (Ferenc Oláh – Getty Images)

The Most Common Signs of Heat Stress in Trees

Keep in mind that there are so many different types of trees across the United States, and each may have its own symptoms. However, there are a few broad signs to look out for, particularly in the leaves. “In general, the most common would be leaf desiccation and wilting,” says Cortese. Desiccation means the leaves are extremely dry due to dehydration.

How do you know if leaves are drying out? First, look at their color. “Some trees will show signs of yellowing in the leaves due to mineral deficiency,” Cortese explains. “Other specific symptoms are leaf scorch and browning of leaf tips, premature dropping of leaves, and stunted growth with smaller, discolored, or thinner twig elongation.” While you may expect browning leaves and leaves on the ground naturally come fall, those are signs of distress when they happen in summertime.

Some trees are more susceptible to heat stress than others, but it all depends on the type of tree and where you live. Much like the plant hardiness zone for a garden, some trees are better for your region than others. While you can see stress in coniferous trees (evergreens like pine and spruce trees), deciduous trees that shed their leaves annually (think: maples, oaks, hickories) are more vulnerable to heat stress.

“Sadly, the damage to the tree carries forward to the next season or two,” notes Cortese. So, if you don’t try to mitigate the issue, the tree will continue to suffer. The good news: Trees can course-correct themselves. So if drought conditions subside, the tree will recover from heat stress on its own. It will even prune itself, discarding the dead branches and leaves.

heat stress in trees

Odilon Dimier – Getty Images (Odilon Dimier – Getty Images)

How to Help a Tree with Heat Stress

If the prolonged heat continues, you’ll want to help your tree. “Creating an artificial rain for these trees would be the best help,” suggests Cortese. Focus on watering the roots, where it is best absorbed and distributed throughout the tree. You can consider an irrigation system, but Cortese warns that many “are very seldom set appropriately for big trees.” The result may be oversaturating the roots, which will actually slowly kill the tree rather than help it.

Another big help is mulch, specifically composted mulch. Spreading composted mulch around the base of a tree will help retain soil moisture and regulate the temperature. But don’t go overboard! “You never let the mulch touch the trunk of the tree, and it only needs to be maybe two or three inches thick,” he says. Start a few inches away from the trunk and layer toward the tree’s drip line (the ground below the outermost tips of the branches).

The one product to avoid using is nitrogen fertilizer. “If you put nitrogen fertilizer on those root systems, it will make the tree grow, but it doesn’t need to be growing full strength at that time,” Cortese explains. Essentially, you want a healing tree to reserve its energy in the root system and not force it to use that energy on pushing out new leaves.

Lastly, remember that when your tree is healing from heat stress, it may not look healthy right away. Cortese describes it like this: “It is like stopping a train; once the brakes are applied, it will slide for a mile or more coming to a stop.” So, it will take the tree a few seasons to recover. But rest assured, between its own natural systems and a little help from you with water and compost, it can recover and live a long, happy life.