It’s easy to see something is amiss with your Japanese Maple when its leaves are bent out of shape. There are quite a few different problems that can result in twisted, shriveled, and bunched-up foliage on these trees. So how can you tell which is which? And what can you do about it? We’ll walk you through the main reasons for curled leaves on a Japanese Maple tree and suggest some possible fixes.
Sudden leaf curl can sometimes result from fungal infections or temperature stress. Discolored, curled leaves on a Japanese Maple could also be due to dehydration, soggy soil, or fertilizer problems. If new leaves are emerging already shriveled and stunted, you might have a pest problem.
Curled foliage is one of a tree’s most common responses to stress. In some cases, it can serve as a defense mechanism, limiting the loss of water by reducing leaf surface area. You’ll need to take into account the tree’s other symptoms and its cultural conditions to identify what’s causing its curling leaves. Here are the most common explanations.
#1: Clusters of Tightly Curled Leaves: Verticillium Wilt
Gardeners are sometimes puzzled to see random portions of their Japanese Maple leaves clenching up like fists. Often, it seems to be affecting some limbs but not others or striking only one side of the tree. The other parts of your Japanese Maple seem to be totally healthy, with no signs of wilting or discoloration.
This can be a sign of a nasty disease called verticillium wilt. It’s caused by soil-dwelling fungi that can invade Japanese Maples through the roots. When they do, they choke off the channels that transport water and nutrients throughout the tree. The uneven distribution of curled leaves on a Japanese Maple often indicates that portions of the tree have started to succumb to verticillium wilt. If you peel back the bark on an affected branch, you’ll likely find streaks of brown or black in the wood, the calling card of this fungus.
We’re sad to report that there is no cure for this disease. Sometimes, it’s best to remove your tree and plant a resistant species instead. The fungus is in the soil, so any Japanese Maple you put there will also be infected. However, it’s not always fatal — a strong, healthy tree can sometimes lock the fungus down and keep it from spreading.
You may be able to prolong your Japanese Maple’s lifespan by keeping it thoroughly watered in hot weather and mulching it to avoid dehydration. Prune your tree to remove infected limbs so pests and other diseases can’t attack the weak spots. Burn or landfill anything you remove from your tree — never compost it or use it for wood chips.
#2: Tan Spots on Curled Leaves: Anthracnose
Anthracnose is another fungus that may attack Japanese Maple leaves. In addition to causing the foliage to shrivel and fold up, this disease creates irregular beige lesions. They typically show up at the edges or along the veins of leaves. Anthracnose most often shows up in the springtime, especially during periods of cool, wet weather. Like verticillium, there’s no cure once the damage shows up. Unlike verticillium, it’s not usually fatal to the tree.
To manage the infection, prune heavily affected leaves (disinfecting your trimmers between cuts) and be careful not to overwater. Make sure you remove any leaves around the base of the tree as they fall. Anthracnose spores overwinter in the leaf litter, so getting rid of detritus reduces the risk of reinfection.
Treating the leaves in spring with a copper-based fungicide can also help prevent the disease from showing back up next year. However, this is probably unnecessary unless your Japanese Maple is very young or under other environmental stress. Leaving adequate room between trees for sunlight and airflow also reduces the risk of an anthracnose infection.
#3: Crispy Yellow or Brown Japanese Maple Leaves: Dehydration
Curled leaves on a Japanese Maple can also mean the tree is dehydrated. This is especially likely if they’re dry, papery, and turning yellow or brown. Dehydration usually results from a combination of hot weather, direct sunlight, and underwatering.
The treatment for dehydration is hydration. Give your tree’s roots a thorough soak, and going forward, check the top one to two inches of soil every few days. Water your Japanese Maple when the ground feels dry. This won’t undo the scorching of the leaves, but most of them should uncurl once they have enough moisture again.
You may also need to give your Japanese Maple more shade to shield it from the sun. These trees often can’t handle a full day of direct sunlight, especially when they’re young. Hanging some shade cloth to protect it from southern and western exposure may help prevent dehydration. And when the weather is particularly hot, make sure you’re checking on the soil frequently so you spot when it’s getting dry.
#4: Leaves Curling After A Cold Snap: Temperature Stress
Japanese Maples begin sending out new foliage fairly early in the spring. This can be great for your garden’s look but can also leave them vulnerable to cold snaps. If the temperature suddenly drops sharply after a warm stretch, your tree’s leaves may get stressed out and curl up.
It’s easier to prevent this issue than cure it. Keep a close eye on the weather report in the springtime, and if it looks like a cold snap is coming, you can:
- Use some frost protection wrap to shield the foliage
- Water thoroughly ahead of the freeze
- Mulch the roots with composted fir bark
- Move potted Japanese Maples into a sheltered but unheated space like a garage
Once your Japanese Maple has been affected by a cold snap, the best thing you can do is give it some water. A frost can dehydrate a tree, just like a spell of intense heat. Making sure it has enough moisture will help it recover.
#5: Lumpy Blisters on Curled Japanese Maple Leaves: Taphrina
This list wouldn’t be complete without one more fungus that can cause curled leaves on a Japanese Maple. The scientific term for this pathogen is Taphrina fungus, but many gardeners simply call it — appropriately enough — “leaf curl”. It deforms the foliage with raised, discolored bumps that pull the leaf edges inward.
Like anthracnose, Taphrina infection tends not to be a serious threat to a tree’s health. It may spoil the aesthetic for a season, but your Japanese Maple should survive. Handle it the same way we recommended for anthracnose: avoid overwatering, prune severely infected foliage, and don’t let leaf litter pile up around your tree’s trunk.
#6: New Leaves Shriveled and Curled: Sap-Sucking Pests
What if your tree’s pushing out new leaves, but they already seem small, stunted, and curled? This most likely means that your Japanese Maple is infested by insects. Creatures like aphids, mealybugs, and scale insects drain the sugary juices from the wood, damaging emerging foliage.
Other telling signs of a pest problem include:
- Deposits of sticky fluid
- Charcoal-colored mold
- Older leaves wilting, yellowing, and curling
- Clusters of small, pear-shaped bugs near branch tips (aphids)
- Bits of white fluff spotting the leaves and branches (mealybugs or scale egg sacs)
- Round or oval bumps on the bark (scale)
If there are only a few pests, you may be able to clear them off with a vigorous spray from a hose. Scale insects will probably have to be pried off the bark with a fingernail (you may want to wear gloves).
More intense infestations might require a few applications of some type of pesticide. Good options include:
- Insecticidal soap — spray on infested branches only
- Horticultural oil — spread over the entire tree, using a two to three percent concentration in the winter or 1% in the summer
- Neem oil — similar to horticultural oil, but you should space out applications by at least five to seven days
Most of these pest killers carry a risk of damaging Japanese Maples. Test them on just a handful of leaves at first and wait a day or two to see the effects. You can reduce the risk by applying in the evening and avoiding days when temperatures are above 90 degrees. Try to provide your Japanese Maple with shade if it doesn’t already have some, and never use these products while your tree’s leaves are still growing in for the season.
#7: Yellowing Japanese Maple Leaves: Poor Drainage
Japanese Maples don’t like to be dehydrated, but they also don’t like standing water. If the soil beneath your tree is too compacted or water-retentive, it may get sludgy and deprive the roots of oxygen. This can cause curled leaves on a Japanese Maple. They’ll often wilt, turn a sickly yellow color, and develop brown or black tips.
One way you might be able to fix this issue is by simply reducing the frequency of watering. If the soil drains slowly, accidentally overwatering your tree is much easier. Avoid giving your tree a drink if the top two inches of soil still feel moist. You should also check to see whether you’ve put too much mulch around the roots. Reducing or removing it will allow water to evaporate faster.
If the tree has only recently been planted, you might be able to dig it up and add some more soil, raising its root ball. When the soil is extremely clay-heavy, or your Japanese Maple is located in a dip in the landscape where water pools, moving it to a better site might be warranted.
#8: Stunted or Deformed Japanese Maple Leaves: Nutrition Problems
Adding too much or too little fertilizer can also cause your Japanese Maple leaves to curl up. Deficiencies in nutrients like nitrogen, phosphorus, and calcium can result in curling foliage along with various types of discoloration. But an excess of fertilizer may damage the roots, causing symptoms similar to overwatering.
Diagnosing a nutrition problem often requires thinking through your care practices and the tree’s environment. If you’ve recently added fertilizer and your Japanese Maple leaves suddenly begin to twist up, nutrient overload could be the problem. This is especially likely if the soil has drainage issues or you don’t thoroughly soak it when you water. You can often flush out the excess minerals by giving your Japanese Maple an extra-long drink.
On the other hand, if your Japanese Maple is in a container and you haven’t fertilized it in years, it might have a deficit. Landscape trees rarely need supplemental fertilizer unless they’re young and growing fast or there’s a specific deficiency in your soil. You can try giving your maple a mild dose of slow-release fertilizer to see if its health and growth rate improve. To be 100% certain that there’s a deficiency, you may need to perform a soil test.
Final Thoughts
Curled leaves on a Japanese Maple tree can point to a wide variety of different problems. We hope this article has helped you figure out which one is plaguing your tree. Luckily, Japanese Maples can be quite resilient. If you’re attentive to your tree’s needs, there’s a good chance it will soon be thriving once again.