Red-leaf Japanese maples turn green if they are delayed greening species, are grown from seeds, experience very hot weather or what you got was not what you thought it was.
Why are Japanese maple leaves turning green again?
There are several reasons why red-leaf Japanese maples turn green. It happens when they are;
- Delayed greening species,
- Grown from seeds,
- Experiencing very hot weather, or
- Not what you thought it was.
Let me explain in detail.
Delayed greening species
If you have species of Japanese maple that changes color from red to green in spring and then to red/yellow in fall, it is perfectly normal that your tree’s leaves are turning green.
Some Japanese maple species sprout in red color in spring. Of these, the leaves of some stay red throughout the season whereas those of others turn green a while after sprouting and turning back to red/yellow/bronze in fall.
The change of color of young leaves from red to green is called delayed greening.
What makes the leaf color
The leaf color of Japanese maple trees reflects 3 pigments in leaves.
- Chlorophyll: Green. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for food.
- Carotenoids: Yellow. It absorbs light in wavelengths that chlorophyll is inefficient at absorbing, such as the blue-green to green wavelengths.
- Anthocyanin: Red. It protects leaves from stress caused by extreme temperatures and attacks from herbivores that may be attracted by green color.
Some young leaves of Japanese maples are transiently red because they accumulate anthocyanins (red pigments) in the leaves when they sprout. Though the causes of delayed greening are not yet fully known, it is an adaptive strategy for plants for sure.
One theory says anthocyanins (red pigments) have a sunscreen function against excess visible light. Although invisible to human eyes, there are chlorophylls (green pigments) in the red leaves. Anthocyanins (red pigments) protect chloroplasts from ultraviolet rays and encourages the development of chloroplasts to produce energy.
Another theory says red leaves give plants protection against herbivorous insects. To some insects, red leaves appear less attractive and discernible, thus lower risk of damage to young leaves. It is known that green leaves are much more susceptible to insect attacks. Also, anthocyanins act as an anti-bacterial agent as well.
In any event, the redness disappears as young leaves mature if you have delayed greening cultivar of Japanese maple.
Grown from seeds
Red-leaf Japanese maples like Shojo Nomura and Bloodgood may turn green if they are grown from seeds.
Will seeds produce trees identical to the tree it was collected from?
Plants grown from seeds may not have the same qualities as the parent trees. Whether the resulting trees are true to the parent tree, i.e. identical to the tree that it was harvested from, depends on whether they were self-pollinated or not.
When eggs are fertilized with pollen from the same tree, the baby trees will each have two identical (or nearly so) sets of genes. They are the exact copies of their parents, and very similar to each other.
On the other hand, if eggs are fertilized with pollen from different trees, the baby trees may not exhibit the same characteristics as parent trees because they have the qualities of both parents.
What about Japanese maple?
Japanese maple can self-pollinate or pollinate from different Japanese maples of the same cultivar or different cultivars. Because growing from seeds is much easier when you want to propagate in numbers, some nurseries sell trees grown from seeds.
It is hard to know by looking at the tree whether it is grown from seeds or not, but it may be the reason for the supposedly red-leaf Japanese maple turning green.
Extreme weather like very hot summer with too much sunlight is known to turn some red-leaf Japanese maples to green. Shojo Nomura, a red-leaf cultivar, sometimes turns green when it is hot.
The red-leaf Japanese maples stay red in a temperate climate with adequate sunlight. But they tend to change color from bright red in spring to bronzy in summer every year if you live in a warmer climate. Warm weather increases chlorophyll (green) which darkens the leaf color to more like brownish.
Lack of sunlight
Also, if you keep your red-leaf Japanese maples indoors, the leaves may turn greenish due to the lack of sunlight (time/intensity). Japanese maples are sun-loving plants that should be kept outside under the sun.
It is sad to say that some shops are deceptive or uneducated; what you think you get may not be what it is. There are so many cultivars of Japanese maples and there is no guarantee that the one you purchased from the shop is indeed the red-leaf cultivar.
Karageorgou P, Manetas Y. The importance of being red when young: anthocyanins and the protection of young leaves of Quercus coccifera from insect herbivory and excess light. Tree Physiol. 2006 May;26(5):613-21. doi: 10.1093/treephys/26.5.613. PMID: 16452075.mature.