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How to know if your trees are stressed

The sun shines through a dense canopy of trees on a blue sky day.
Phineas Pope
/
IPR

Trees are tough - but they still need love. Learn how to spot the signs of stress to keep your trees healthy and happy.

Trees can take a lot - hammocks, treehouses, swings, hail, even an occasional derecho - but they're not invincible. There are signs to look for to understand if a tree might be damaged or getting insufficient nutrients or water.

Chelsea Harbach, a Plant Disease Diagnostician at Iowa State University, says it's all about understanding what's normal. She says with any plant (not just trees), research and learn about what it should look like and understand normal changes that occur. From there, it's only a matter of watching for irregular changes and abnormalities.

How to track changes

If you see something off, take note, and don't freak out. Harbach recommends using your smartphone to capture photos over a period of time to track spots you want to watch in your plants. Photos on smartphones are automatically timestamped, so you'll be able to understand how quickly changes occur. If you're old-school, you can start a plant journal, and include descriptions, photographs and even leaf samples. This can almost be a scrapbook of the life of the tree(s).

Spot the signs

Harbach says to look for changes in foliage color, canopy density, stems and cracking bark. Keep track of the progression, but don't feel like you need to diagnose the issue. Just as you trust your doctors to diagnose illnesses, you should trust horticulture specialists, disease diagnosticians and arborists to diagnose issues with your trees. Specialists will be able to give you management techniques and the right tools to help.

It might not be disease

Being conscientious of your tree's root system - and how it expands away from the tree - is important. You don't want to compact the ground over those roots. Even parking your car in the yard where roots may be could be enough to cause significant and irreversible harm.

It's also important to know that stress from compaction - or other issues - may not present itself right away. There's a latency period before you'll start to notice the signs of stress. Being a good tree owner means caring for your tree above - and below - ground.

Though tree diseases can be a concern, Harbach says the majority of issues that present themselves through noticeable change are a result of environmental change. Iowa's ongoing drought conditions are a big issue, and are resulting in dehydrated trees.

What can I do to prevent dehydration in trees?

Lots of problems that arise in trees are simply due to dehydration. If you're concerned that a tree is not getting enough water, look for signs of stress. This can include defoliation, browning leaves, and leaves that curl or wilt.

One of the best tips for preventing dehydration is to work in a mulch base. Mulch reduces evaporation, helping preserve some moisture in the ground. It also helps with keeping weeds down, keeping lawnmowers away and can introduce some organic matter back into the soil. For the best results, and if feasible in your landscape situation, try to mulch out to the tips of the branches.

But it's not just mulch OR watering the tree, it's also how you water. Here's the experts' advice on watering.

Water around trees - not just their base!

Jeff Iles is a horticulture specialist at Iowa State University. He says for newly planted trees, the most important thing is consistent watering. Even after trees have been in the ground for a few years, they can always use some more help - and proper irrigation is key.

Iles says one of the biggest mistakes in watering a tree is not applying water to the entire root system. As a tree develops, the radius of its root zone expands outward more than downward. As a result, watering only at the base of a tree is practically helpful for only very young trees.

How often should I water my trees?

For newly planted trees, expect to be watering four or more times a week. In cooler areas with consistent rainfall, that number may drop to about three times a week. Even trees that have been in the ground for a few years still benefit from being watered deeply about once a month, especially during long dry spells. Keep in mind that it's not an exact science though - it all depends on the environment.

Iles also says to be mindful to not swamp (overwater) the area, as that can create openings for other issues to arise, such as mildew and fungus.

What should I use to water trees?

Nothing beats getting outside with a garden hose and covering a large area. It's the best way to ensure enough water is being distributed over the tree’s roots. Tree watering bags are useful for young trees, but really serve no useful purpose once the tree expands its root base. For those of us who just don't have the time to stand outside, Iowa State University Consumer Horticulture Specialist Aaron Steil places spot sprinklers at the bases of trees in his own yard.

"It will water the entire root zone...It has the same effect as standing there with a hose and watering, but I get to do something else instead," said Steil.

When should I water?

Water early in the morning, before the temperature rises too much. This will give trees a chance to absorb the most moisture they can. If you water in the afternoon, more moisture will evaporate into the atmosphere instead of soaking into the ground and helping the trees.

You may be wondering why you have to water, instead of just waiting for the next rainstorm. While rain is essential, trees benefit more from consistent watering - especially younger trees. During long dry periods without rain or watering, trees will suffer and begin to die. So get out there with your hose, and give your trees a well deserved drink.

Phineas Pope served as a digital production assistant at Iowa Public Radio from 2023 - 2024.