Is Your Japanese Maple Looking Scorched?
At the nursery I manage, we get quite a few questions about browning, curling and scorched leaves on Japanese Maples. Regarding this problem, there's some good news and some bad news.
THE BAD NEWS FIRST...
Bad news is, if the leaves on your Japanese Maple are looking scorched and raggedy towards the end of summer there's nothing you can do to make them look better.
GOOD NEWS IS...
If your Japanese Maple has leaf scorch, but the tree is still alive, there's most likely nothing to be too worried about. It could just be a temporary problem due to heat and sun stress from a long and hot summer. Japanese Maples usually recover fine from this but won't put out new foliage until the following spring. That being said, if the "root" cause (pun intended) of the browning or bad looking leaves is consistently wet soil, your tree could have a very serious problem with its roots: root rot. However, if you followed proper instructions when planting your Japanese Maple this shouldn't be the problem. If you know you planted it correctly to begin with but the drainage has changed since planting time you could still have a soil moisture issue.
Causes of Leaf Scorch
First, rule out a soil moisture problem.
Though they appreciate moderately damp but well-drained soil, especially during the first two summers or so after having been planted in your landscape, Japanese Maples HATE wet feet. Too much water around the roots for too long and diseases such as root rot can set in.
So, first, you'll want to rule out a problem with the root system that could be caused by wet, oversaturated soil. If the leaves of your Japanese Maple have slowly turned brown or black, starting from the tips and working towards the base of the leaf, this could be an indicator of root rot.
To check for soil moisture there's no better way than to use the finger test. Some moisture meters will work, but cheap ones don't always provide accurate readings. You can also use a small hand trowel to dig a small hole around the roots. If the hole fills with water, you've got a problem. If it's summer and you haven't watered for a few days, there's been no rain, and the soil is really wet, you've might have a soil moisture problem.
If the soil is too wet, and the stems and branches on your Japanese Maple have begun to die, their might not be much you can do to save the tree. To check stems or branches for signs of life, starting towards the top of the tree, use a knife or the edge of a coin to scrape away a very small section of bark on the stems. If the underlayer is green there is life, if brown or tan color the branch has died. Continue this process moving downwards on the tree to see what is still alive. If over 50% of the tree is dead there isn't a good chance of long term survival. This doesn't mean you can't attempt to restore the tree to health by replanting it. In attempting to save your tree you'll need to "lift it up." This means replant the tree at a higher level in the soil. In some cases it will be necessary to replant the tree with half or more of the rootball above ground level, then gradually tapering your soil mixture from the top of the root ball to ground level. Essentially, you will be replanting your tree into a "raised mound." This will allow the roots to grow down to the water table instead of standing in it.
If the leaves of your Japanese Maple are browning on the tips or are scorched looking and curled, but the branches are still flexible and alive, the leaf scorch could be caused from:
- Too much sunlight
- Excessive heat
- Water on the foliage during the afternoon hours of the day
- Chemical applications
- Over-exposure to sunlight
Exposure to sunlight
Most, but not all Japanese Maples prefer some shade during the day. In their native habitat, Japanese Maples will be found growing along partially shaded woodland borders or just under the canopies of larger trees. There are some varieties that have demonstrated a good resistance to all day exposure to sun, even in the southern US.
But, if your Japanese Maple is planted in all day direct sunlight, and year after year the leaves become scorched during the summer, chances are you have a variety that prefers some shade. To determine what exposure to sun your particular variety of Japanese Maple prefers in your region do some research on the Internet or ask your professional local nurseryman or landscape contractor.
As for a long-term remedy for leaf scorch caused by over-exposure to sun, if your Japanese Maple is a variety that prefers shade, you might have to relocate your tree. The only other alternative would be to plant a larger tree to the west side of your Japanese Maple that would provide shade during the afternoon hours. NOTE: When your tree has leaf scorch, be careful not to over-water it. Leaves with leaf scorch are no longer drinking water. Just keep the soil moderately damp.
As with many other types of plants and trees, excessive or prolonged periods of heat can cause leaf scorch on many varieties of Japanese Maple. But there's not much you can do about an unusually hot summer and, as previously mentioned, not much you can do about leaf scorch. Your tree will drop it's leaves in fall and fresh new leaves will emerge the following spring. Then say a prayer that next summer won't be quite so hot!
Water on foliage
If it's not the sun or heat scorching the leaves, the cause of leaf scorch could be caused from water having been splashed on the leaves during the hottest part of the day. This problem can be solved by timing an automated irrigation/ sprinkler system to run during the morning hours or making sure not to splash water on foliage when hand watering during the late morning or afternoon hours. Too, do not splash water on the foliage of a Japanese Maple at night as this can lead to damaging fungus or disease. The best time to water is early to mid morning.
Japanese Maples are very sensitive to many types of chemical insecticides and fungicides. Because they don't have any serious problems with insects or disease, chemical applications should be avoided. That being said, if you must spray for insects, such as the Japanese Beetle, use only a mild solution of Sevin (Carbaryl) spray, or other insecticide listed for use on Japanese Maples. To reduce the possibility of leaf scorch, make sure to spray only in the early morning hours.
If you think your Japanese Maple has a serious problem, and you're not sure if it's leaf scorch or some other disease, don't hesitate to consult with your local arborist, professional nurseryman, or local extention service agent.