Trees are living organisms that require many proper conditions to thrive. At first glance, it may seem that they are not fastidious and require little care, but this is not always the case. This is especially true for cultivated forms of Acer palmatum.
Mineral deficiency is the main reason for the yellowing of Japanese maple leaves. If the soil lacks iron, zinc, or magnesium, the tree can develop chlorosis. The symptoms will be yellowing of the leaves of the Japanese Maple.
There are also a number of other problems that can cause the leaves to turn yellow. These problems and their solutions are described in detail in this article.
Lack of minerals
If the Japanese maple doesn’t get iron, zinc, and magnesium regularly, it will develop chlorosis. This is a disease associated with the plant’s inability to photosynthesize and produce chlorophyll for normal growth.
The causes of chlorosis can vary. For this reason, the problem must be studied and solved holistically.
The first cause is a banal lack of nutrients in the soil. This means that the soil is poor and unable to meet the nutritional needs of maples.
The second reason is too alkaline soil. In this type of soil, the tree is not able to consume the necessary minerals, even though they are present.
Another cause of chlorosis is overwatering. We will talk about this in a later chapter.
How to fix
To quickly improve your tree, spray foliar fertilizer directly on the leaves. You can find special products on the market that contain iron and are designed specifically for the treatment of chlorosis.
Next, you need to buy a pH test kit. Use it to find out what kind of soil you have. If the soil pH is above 7.0 use aluminum sulfate or garden sulfur to get it down to at least 6.0-6.5.
The next step is to fertilize the Japanese Maple with a slow-release fertilizer. Make sure the product contains nitrogen, phosphorus, potassium, iron, magnesium, and zinc. Usually, manufacturers of such products make them complex, which means they contain all the above minerals.
One such fertilizer per year is enough for normal growth. But don’t fertilize late in the season.
You can also add liquid iron chelate to your maple. This usually solves the problem of chlorosis fairly quickly if it is due to iron deficiency.
There are a number of diseases that affect the Japon maple. Most of them cause the leaves to turn yellow or become discolored.
Usually, yellow spots appear on the leaves first. Depending on the disease, the spots can be small or cover most of the leaves.
Over time, the spots will turn brown and their yellow edge will expand. Sometimes the entire leaf may turn yellow and fall off.
How to fix
Constantly monitor your maple for spots or other unhealthy signs on both leaves and branches.
Provide good ventilation around the crown. Don’t plant trees too close together.
If yellow or brown spots appear on the leaves, spray them with a multi-purpose fungicide. After about a week, repeat the spraying with copper fungicide.
For more information on the major diseases that can cause leaf yellowing, see Japanese Maple Diseases.
Overwatering is the next cause of yellowing of the Japanese Maple. The reason is that if the roots are left wet for a long time they lose their ability to absorb minerals and chlorosis occurs as a result. We already talked about chlorosis in the first chapter.
The second thing that can happen is root rot. In this case, water is not coming to the leaves and they not only start to turn yellow but also dry, i.e. brown.
How to fix
The first thing to do is to stop watering frequently if this is the reason for overwatering. Next, only water the Japanese maple when the soil in the root zone is more than two inches dry.
If the soil around the roots is wet due to proximity to water sources (pond, roof water, etc.). Divert excess water away from the root zone by digging a drainage trench around the maple.
Poorly drained soil can also cause overwatering and root rot. In this case, you need to transplant the Japanese Maple to a more draining soil in a less humid location, if possible of course. Read how to do this correctly in the article How to Transplant Japanese Maples Properly?
Too much sun
The yellowing of the Japanese maple in summer is the result of too much sun. Especially if the soil around the tree was dry or not moist enough at the time.
As a result, yellow spots may appear on the leaves. In the worst case, the maple will get brown burns in the form of large spots. The rest of the leaf will turn yellow and it will die.
This usually happens to trees that have not yet been fully established or are weakened for some reason. There are also varieties of Japanese Maple that need partial shade.
How to fix
Water the maple with enough water to soak up the soil around it. Next, watch the soil for moisture and don’t let it dry out more than 1 inch. Stick to this recommendation only during the extreme heat of summer.
Mulch the root zone with pine bark or wood chips about 2 inches thick. Avoid putting mulch on the tree trunk.
Provide shade over the maple tree during the worst of the heat. If the tree is small, transplant it next spring to a place with morning sun and afternoon shade.
There is a certain type of insect that feeds on the sap of trees and other plants. These include aphids, scale, mealybugs, spider mites and some others. All of them are very fond of parasitizing Japanese Maple.
As a result of their activities, the leaves do not get enough sap and become discolored. If nothing is done, the leaves will begin to turn yellow. The situation is aggravated by heat and underwatering.
How to fix
If you see insect colonies on your maple, try to wash them off with water. Pests like the scale are best removed with your hands because they are firmly attached to the branches.
Next, spray the entire maple with insecticidal soap. This product is easily available on the market. Repeat the spraying after 2-3 weeks.
For more on pest control, see What can I spray on my Japanese maple for bugs?
Yellowing after transplanting
It is very common for Japanese maples to turn yellow after transplanting. This is caused by the wrong timing or damage to the root system. The weather also has a great deal to do with this issue.
If you make mistakes in transplanting, the maple may not respond immediately. However, over time, the leaves will begin to turn pale and yellow.
How to fix
After transplanting, shade the Japanese Maple for a few weeks. Both a garden umbrella and a shading net will be equally suitable for this.
Water the newly transplanted maple as soon as the soil is a little more than an inch dry. Mulch the surface around the trunk with organic matter, but do not put it on the trunk.
You can read more about this issue in the article How to Avoid Japanese Maple Transplant Shock?