Any gardener’s heart is bound to sink at the sight of a once-healthy Japanese Maple shriveling up and turning brown. It’s especially distressing when you thought the tree was in great shape. Crispy Japanese Maple leaves can come from a few different kinds of health problems. Your tree isn’t necessarily doomed, but figuring out what’s wrong is crucial for nursing it back to health.
Environmental conditions like drought, harsh winds, and sun scorch can cause brown and crispy Japanese Maple leaves. An excess of fertilizer may also dehydrate your tree. Another possibility is that your Japanese Maple has pests such as aphids or scale, or a disease like verticillium wilt.
You’ll need to assess your tree’s health and growing conditions carefully and take an inventory of your gardening practices to diagnose the problem. Sometimes the solution may be as simple as giving the plant a big drink of water or a bit more shade. But knowing what you’re dealing with is always step one. Let’s review the main causes of curled and crunchy Japanese Maple foliage.
#1: Bright Sunlight Can Burn Japanese Maple Leaves
Plants love sunlight, but not all of them love direct sunlight. Japanese Maples evolved in dense forests where they received a good amount of shade from the taller trees above them. If yours has very little sun protection, hot weather could dry out the leaves rapidly, causing crunchy dead spots. The risk is particularly high when your tree is a seedling or a juvenile.
Take a look at your Japanese Maple’s light exposure. Is it exposed on the west and/or south side? If so, it’s getting the unfiltered rays of the sun during the hottest parts of the day. You might notice that most of the browned or bleached spots are on the sunny side. This is a dead giveaway that sun scorch is the issue. In some cases, the bark may be burned along with the leaves.
Sunburn doesn’t always mean your Japanese Maple is dying. It may be able to bounce back if you get it some shade. If you’re growing your Japanese Maple in a container, try moving it below a bigger tree or into the shade produced by your home. The ideal spot is one where most of the light is coming from the east or north side. Hanging some shade cloth could be a workable option for trees rooted in the ground.
Though your Japanese Maple should hopefully recover once you shield it from the light, the burned leaves will stay burned. It’s a good idea to snip off any that are fully fried. Otherwise, they’ll keep draining energy from the tree and may attract pests. You can leave any healthy tissue in place since it’s still photosynthesizing and helping your Japanese Maple.
#2: Drought Makes Japanese Maple Leaves Crispy
Lack of water is another major cause of dry, brown foliage on a Japanese Maple. It goes hand in hand with the problem above — sun scorch is essentially rapid dehydration due to heat. When the sun and the thermometer are high, make sure you’re watering your Japanese Maple thoroughly. Again, this is especially crucial during the first decade after planting, when it’s growing faster and using more water.
You can perform a quick test with your finger to see if the top 1-2 inches of the soil are dry. To test further down, try a moisture probe. The ground should be lightly damp 6-8 inches below the surface. If it’s dry, give your Japanese Maple a long, hearty soak, getting all the way around the trunk. (Try not to get water on the leaves or the bark, though.)
When your tree is young, it’s best to test the soil every 3-4 days during the growing season. You can increase that to every 1-2 days during hot weather. Older Japanese Maples are better able to hydrate themselves, but you should still watch the soil during heat waves. And trees in pots never grow out of the need for watering.
As with sun scorch, watering won’t fix your crispy Japanese Maple leaves. But it should stop your tree from continuing to dry out and allow for healthy growth next year.
Note: Overwatering vs. Underwatering
It’s important to be sure that your tree is actually thirsty, because overwatering Japanese Maples is also bad. The symptoms can look somewhat similar: both conditions cause the foliage to wilt, yellow, and brown.
Feeling the foliage can give you a hint about what’s going on. Brittle, crunchy Japanese Maple leaves are more likely to come from overwatering or sunburn. Overwatered leaves often feel soft and limp.
Your soil test may be even more revealing. If your Japanese Maple looks dehydrated, but the earth around it is still wet, you’re almost certainly dealing with overwatering. Let it dry out, and hope your tree recovers. If it’s relatively young or growing in a pot, consider replanting it with better drainage once the leaves drop for the winter.
#3: Windburned Japanese Maple Leaves
Sunlight isn’t the only environmental stressor that can dehydrate Japanese Maple leaves. Dry wind may have a similar effect. The rapid air currents pull moisture away from the leaf surface, leaving it brown and crunchy. This is especially common in the summer heat, but a windy enough spring can also be problematic.
If your crispy Japanese Maple leaves appeared right after a burst of windy weather, there’s a strong possibility they’re wind-burned. The dry areas often appear in the gaps between leaf veins.
You can move potted Japanese Maples into the lee of buildings, trees, fences, or some other kind of shelter. The best safeguard for trees rooted in the earth is frequent, thorough watering during the windy period or right after. This is also how you should revive your Japanese Maple after it’s wind-burned.
If you’re able to set up some kind of additional windbreak for your landscape trees, they may appreciate it. Permanent options include shrubs and fences, while sturdy, well-anchored shade cloth might work as a temporary measure.
#4: Too Much Fertilizer Can Fry Your Foliage
Like all plants, Japanese Maples need nutrition, but more isn’t always better. High concentrations of mineral salts from fertilizer can interfere with the osmotic flow of moisture into the roots. When they build up enough, they may actually leach water away from the tree.
If you’ve been giving your tree lots of synthetic fertilizer to get it to grow faster, you may have damaged it. Even a normal dosage can be a problem if the excess minerals don’t get washed away. That can happen if you’re not soaking the roots enough when watering or if the soil has poor drainage.
Fertilizer burn often damages the tips of leaves first, causing them to shrivel up and blacken. (This can also be caused by overwatering, so check for that too.) If the problem persists, the rest of the leaf will start to crisp up and die.
When you suspect your Japanese Maple is over-fertilized and you’ve ruled out overwatering, the best cure is a big drink. Give your tree an extra-long soak, using 3-4 times as much water as you’d normally provide. Provided the soil has decent drainage, this should help flush most of the surplus salts away.
Moving forward, it’s probably best to fertilize your Japanese Maple more sparingly. A single application of slow-release granular fertilizer in the early spring will usually last your tree all year.
#5: Some Pests Can Cause Crispy Japanese Maple Leaves
To us, your Japanese Maple is a beautiful work of art. But there are lots of creatures that will see it only as food. Certain garden pests can drain the sugary juices from the leaves, creating effects similar to drought or sunburn.
Aphids
These pests are a scourge of gardens everywhere, and Japanese Maples are among the many plants they can attack. Aphids are small, water-balloon-shaped insects that tend to feed in clusters along branches, especially on newer growth. They can come in lots of different colors, though the most common varieties on Japanese Maples are green and yellow. You may also see their white and flaky discarded exoskeletons, which make your tree look like it has dandruff.
Small colonies of aphids can often be cleared away by blasting them off with a hose. Try not to do this in full sun, because water droplets on the leaves can magnify the sunlight and burn the leaves. For more extensive infestations, spraying the foliage with insecticidal soap may be necessary. It’s also often helpful to encourage beneficial insects in your garden to hunt aphids and other pests.
Scale
Scale insects look more like warts than bugs. These armored insects clamp onto the bark and stay fixed in place for the rest of their lives. They tend to have a waxy coating that makes them look brown, gray, or black. The ones that most commonly feed on Japanese Maples are white, with a curved, oyster-shell shape. Scale also secrete a sticky slime called honeydew.
If there are only a few scale, you may be able to scrape the adults off with your gloved hand. Take a bucket of water with you to drown them. Then use a hose to wash away the juvenile insects, which are too small to see with the naked eye. When that doesn’t do the trick, you may need to wait until winter dormancy and apply horticultural oil.
Mealybugs
These nasty critters are related to scale insects, but instead of hard armor, they’re covered with a cottony-looking white wax. Since they crawl around instead of locking themselves in place, they can be surprisingly good at hiding.
Mealybugs often target scars or splits in the bark, such as wounds from improper pruning. Like scale insects, they produce honeydew. Heavy mealybug feeding can produce lumpy growths in the wood as well as crispy Japanese Maple leaves.
Spraying the tree off with water is a good start. You may need to follow it up by wiping down the adult bugs with a cotton pad soaked in rubbing alcohol. Yes, this is lengthy and frustrating, and yes, it’s often necessary. Finish the job with some insecticidal soap to kill the juveniles.
Spider Mites
These insidious creatures are so small that they may go unnoticed for a while. They tend to hide on the undersides of leaves, targeting stressed or newly transplanted trees. As the mite population grows, you may notice wispy, dusty-looking webbing on the foliage. The leaf damage is easier to spot — it looks like an irregular fading or bleaching of the leaves, causing them to curl up and turn brown where it’s most severe.
The same combination of water spray and insecticidal soap that works on aphids should also get rid of spider mites.
The Best Offense Is a Good Defense
The treatments described above may not be enough to completely rid your Japanese Maple of pests. Sometimes you’ll have to repeat them multiple times before you see success. You’ll be much better off if you can stop these bugs from getting a foothold in the first place.
Creating a garden filled with pest-eating beneficial insects can be part of that strategy. But it’s also important to keep your Japanese Maple in good health overall. A sickly tree is much more likely to be targeted by bugs. Giving your tree good soil, a mildly shady location, and the right amounts of water and fertilizer will go a long way toward keeping it pest-free.
If your Japanese Maple is in good shape, it may be able to shake off a pest infestation. Sometimes the winter cold is enough to do it, especially for bugs like spider mites that love hot and dry weather.
#6: Crispy Leaves From Verticillium Wilt
Some fungal diseases can be as bad or worse than insects. Verticillium wilt is one of the nastiest. It gums up your tree’s inner workings, blocking the flow of water and nutrients. This can cause abrupt wilting and dehydration, resulting in crispy Japanese Maple leaves appearing seemingly out of nowhere.
Verticillium wilt can be tough to recognize since it grows inside the tree instead of on the surface. When you notice lots of leaf and branch dieback with no obvious cause, clip off one of the dead branches. When you peel back the bark, do you see black rings or streaks inside the wood? If so, your Japanese Maple is infected with verticillium.
Unfortunately, there’s no reliable cure for this disease. Your Japanese Maple responds by closing off the channels in its tissues that the fungus uses to spread. You can help by cutting off dead branches and burning them or discarding them in a landfill. Never compost them, and always disinfect your shears with rubbing alcohol or bleach between cuts. Keep your Japanese Maple well-watered since the disease tends to dehydrate it.
Once again, prevention is much better than treatment. Verticillium spreads through the soil, through unsanitized pruning tools, and from one infected plant to another. Be careful about using wood chips, mulch, or plants from unreliable sources. After an infection, make sure not to move soil from that spot to another for at least 10 years afterward.
#7: Being Root Bound Can Kill The Leaves
In some cases, the roots of a Japanese Maple can pack tightly together and even wrap around each other, cutting off the flow of moisture and nutrients. This affects the leaves much like fertilizer burn. We call this being root bound.
This problem is far more common with Japanese Maples in containers. However, it can also be an issue with landscape trees from nurseries if you don’t check the roots before planting.
Take your Japanese Maple out of its pot and look at the root system. It’s normal for them to be a bit cramped, but if they’re so densely packed that there’s little room for potting mix in between, you have a problem. Be especially wary of girdling roots that are snaking around the edges.
Fix this issue by cutting through the root mass with a disinfected pruning saw on all four sides, from top to bottom, creating a “box cut”. Then replant in fresh potting mix, and consider increasing the pot size by about 2 inches.
If your Japanese Maple is already well-established in the ground, the problem is harder to fix, but maybe not impossible. You can often see the girdling roots right at the soil line or below the mulch pile. Sometimes they’re small enough to cut through with a saw or a pair of loppers, rescuing the tree. For large girdling roots on a well-established Japanese Maple, you may be better off consulting an arborist.
Crispy Leaves Don’t Always Mean Your Japanese Maple Is Dying
Though it’s alarming when your Japanese Maple’s foliage begins to show signs of stress, it’s not necessarily a death sentence for the tree. After all, Acer palmatum and its cousins are deciduous trees. Shedding foliage and growing it again is what they do.
Japanese Maples often proactively cut off the flow of energy and nutrients to their leaves in response to stress. This defense mechanism lets your plant conserve its resources and come back stronger the next season. Once you identify and correct the problem, there’s a very good chance your Japanese Maple will soon resume healthy growth.