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How to Treat Trees for Heat Stress

During a heatwave, people are advised to stay inside, drink plenty of fluids, and find ways to stay cool. The effects of hot weather, heat exhaustion, or heat stroke are easy to see in humans—flushed skin that’s hot to the touch, a heat rash, high body temperature, fainting, and so on—and trees have their own signals and markers as well.

Since a tree can’t move into the shade or pour another glass of iced tea for itself, it’s up to us to help them through extreme heatwaves so they can continue to give us shade and look their best. So how can you treat your trees for heat stress in the hottest time of the year?

Here are our favorite tips for treating your tree for heat stress:

1. What Are the Normal Operations for a Tree?

Normally, a tree will absorb the water in the soil around its roots, and eventually, that water will travel throughout the whole tree, spreading nutrients and sugars. Then, the water will evaporate from the leaves in a process called transpiration. Consider it a little like when a human sweats, known as perspiration. This process cools the tree down. Just like when you go for a run, it feels nice when you catch a breeze later and your sweaty skin suddenly feels pleasantly cool.

Transpiration is also the reason why it’s a few degrees cooler if you sit beneath a tree. That water vapor is in the air, cooling the tree down.

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2. What Is Heat Stress and How Can You Tell If Your Trees Have It?

So how can you tell when your trees are asking for your help? If they’re succumbing to heat stress, there are plenty of ways that they show it. Heat stress occurs because your tree doesn’t have the water it needs to produce those sugars and process or move those nutrients. As the heat rises and the water in the tree evaporates, your tree will attempt to conserve water and will stop sending water to its leaves.

The leaves of your tree will then start to look wilted and droopy. They will turn yellow and brown—possibly at irregular intervals around the tree or uniformly throughout the tree, depending on how severe the heat stress is. You may also discover there are rust-colored spots or bumps on the tree’s leaves. In extreme cases, the edges of the leaves may look crispy or scorched.

Green leaves may start to fall off your tree, without turning yellow or brown first. This is the tree cutting its losses since all of its moisture is lost through its leaves. Dropping those leaves early is a way for the tree to retain that moisture that would otherwise be lost.

3. Once You Notice One or More of These Symptoms, You Should Act Quickly, If Not Immediately

First, when you discover your tree is suffering from heat stress, give it a good long drink. Make sure you find the drip line for your tree and get water to all the roots. At the very least, water the tree several feet away from the trunk. This is where the tree will receive the most benefit.

However, if you water at the drip line of your tree—the area furthest from the trunk of the tree while still being under the tree canopy—your tree should perk up quickly since that’s where most of the roots are. In a drizzle or rain, the leaves gather water and drip onto the grass, under which the tree’s roots can absorb it. If you water the trunk of your tree, hardly any of the roots benefit from that water you’re giving them.

4. Be Proactive and Mindful So Your Tree Doesn’t Suffer During the Next Heatwave

Once your tree has had a good long drink, take note of how warm the weather has been lately and recall when you watered last before you noticed it was in trouble. This way, you can be proactive about your watering habits when the weather does something similar. As climate change continues to disrupt weather patterns around us, we can expect more intense extremes, both to the hot and cold. The hots will get hotter and the colds will get colder. Keeping an eye on your trees and how they’re handling the heat will help them survive future heatwaves without having to drop their leaves to get your attention.

Another thing to be aware of is how old your tree is. If it’s fairly young and not considered “established,” it will need more water than an older, mature tree. Trees need water to grow their root network. Once it’s grown, maintaining that root network doesn’t take as much water or energy. Giving your tree enough water ensures that it will have a good reservoir to draw from if it goes through a dry spell.

Take a little time to do some research as well about what kind of tree you have. Some trees appreciate having “wet feet,” and others find it difficult to manage. It would also be good to know what type of soil you have. If you have something that’s more like clay, it could take longer for water to penetrate than if you have a sandy loam instead.

5. Make Sure You Are Deep Watering Your Tree

If you have a sprinkler system installed, you’re watering your lawn and other plants nearby. And the water from the sprinkler may land where the tree’s roots are. But this kind of watering can feel more like a spritz from a water bottle, instead of a good, solid drink from a glass.

Following the drip line, take your hose, and spray the ground where the roots of the trees are. You don’t have to water until the ground is muddy, but it should be obvious that you’ve spent some time there with the hose. If you normally water every other day or every third day, you can increase your watering in the summer.

If your tree doesn’t bounce back after a thorough watering, contact a professional tree company such as Mr. Tree for assistance. An experienced arborist will be able to assess the state of the tree and know the best way to help it recover.