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Not every tree can handle a full day of sun in our hot dry summers. Trees like this Japanese maple benefit from an hour or two of afternoon shade.

Courtesy Meredith Seaver, USU Extension

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Finely dissected leaves are more vulnerable to our hot, dry summers and can scorch (dry) easily.

Courtesy Meredith Seaver, USU Extension

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These oak leaves are a good example of how the appearance of summer leaf scorch can vary between different species.

Courtesy Meredith Seaver, USU Extension

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We have a dwarf Japanese maple in the backyard that gets at least six hours of sun and part shade. It has been there for about 15 years and has been very healthy. It is not as full as it used to be. Could the heat be doing the damage to it?

I have noticed that the leaves are crispy and there is some black on the tips. I looked online and it said that it may be getting too much water. Recently I have stopped watering four days a week and it just gets the sprinkling system water about once a week. The other day I noticed new leaves on the bottom of the trunk that seem normal and healthy. I have not taken the crispy leaves off. I’m worried about losing our little tree. Do you think I can do something to help it?

What I see in your photos looks like summer leaf scorch, a common problem for trees here. Episodes of unusual heat can certainly make the problem worse, but there are a few other things contributing to this problem.

• Finely dissected leaves like these are much more prone to this problem.
• Japanese maples are not well suited for our hot, dry climate.
• In our climate, these trees need to be understory or part-shade trees. They’ll be fine with direct sun during the first half of the day, but if the tree is getting more than an hour or two of midday to afternoon sun, that may be too much for the tree.
• Frequent watering can affect the health and function of the root system, making it difficult for the tree to move water efficiently.

There isn’t anything you can do about the leaves’ shape, our climate or where the tree is planted now, but you can do something about the way you’re watering.

Your tree and surrounding plants were being overwatered. If your lawn is on the same schedule, it is being overwatered, too. Established trees and shrubs should be watered deeply but not more than once a week during the summer and less often in the spring and fall. Frequent watering makes it difficult for air to move down into the soil to bring oxygen to the roots. Roots can suffocate or develop root rot diseases, making it difficult for the tree to move enough water up to the leaves. It also makes the tree more susceptible to nutrient issues. The damage and stress from frequent watering can leave trees more susceptible to borers, bark beetles and other pests, too.

When trees are planted in the lawn, if they must be watered on the same schedule along with the lawn or if they have their roots out in the lawn, it’s important that the lawn be watered deeply but as infrequently as it will tolerate. Unless the soil is sandy, most lawns can go three days or more between waterings if they are watered deeply and mowed tall with a mulching mower.

I recommend you gradually transition your tree and lawn to less frequent watering by watering deeply three days a week for a week or two, then twice a week for another week or two. At that point, we’ll be entering fall weather, and you’ll continue to space out your watering by watering every four to five days for a couple of weeks, then every six to seven days, etc., until you’re watering deeply once every eight to 10 days when it’s time to shut off your sprinkler system.

The other thing I recommend for the health of your tree is to keep a 3-inch layer of bark nuggets over the soil in that bed. That will conserve moisture, keep the soil cooler and eliminate the swings between moist and dry. The mulch layer isn’t just helpful for your Japanese maple; the tree is also sharing the planter bed with other plants that need watering. Maintaining that mulch every year will also make it easier to keep your annuals and perennials happy.

This year’s leaves will drop early, but next year your tree will leaf out with new, healthy foliage. With mulch and proper watering, you can expect to see less summer scorch on your tree.