By: Heather Rhoades
While leaves changing color in the fall is wonderful to watch, it does beg the question, “Why do leaves change colors in the autumn?” What causes lush green leaves to suddenly change into bright yellow, orange and red leaves? And why do tree change colors differently year to year?
There is a scientific answer to why do leaves change colors in the autumn. The fall leaf life cycle starts with the end of summer and the shortening of the days. As the days get shorter, the tree does not have enough sunlight to make food for itself.
Rather than struggle to make food through the winter, it shuts down. It stops producing chlorophyll and allows its fall leaves to die. When the tree stops producing chlorophyll, the green color leaves the foliage and you are left with the “true color” of the leaves.
Leaves are naturally orange and yellow. The green just normally covers this up. As the chlorophyll stops flowing, the tree starts to produce anthocyanins. This replaces the chlorophyll and is red colored. So, depending at which point in the fall leaf life cycle the tree is in, the tree will have green, yellow or orange leaves, then red autumn leaf color.
Some trees produce anthocyanins faster than others, meaning that some trees skip right over the yellow and orange color stage and go straight into the red leaf stage. Either way, you end up with a brilliant display of leaves changing color in the fall.
You may have noticed that some years, the fall leaves display is absolutely magnificent while other years the leaves are positively blah — brown even. There are two reasons for both extremes.
The fall leaves’ pigment is susceptible to sunlight. If you have a bright, sunny fall, your tree will be a little blah because the pigments are breaking down quickly.
If your leaves end up brown, it is because of cold. While leaves changing color in the fall are dying, they are not dead. A cold snap will kill the leaves the same as it will on the leaves of most your other plants. And just like your other plants, when the leaves are dead, they turn brown.
While maybe knowing why do leaves change colors in the autumn may take some of the magic out of leaves changing color in the fall, it cannot take any of the beauty away.
This article was last updated on
Read more about General Tree Care
Autumn is a second spring when every leaf is a flower.
I like to think of fall from an Alice In Wonderland perspective. That is, autumn is a time when we shrink in proportion to our gardens while the leaves ‘bloom’ above us. And every year nature charts new territory, unveiling color schemes so daring they leave little doubt as to her ability to create designs far superior to our own.
The beauty of nature is sometimes found in the profound ‘intelligence’ it exudes. Perennials, which includes trees, must protect themselves in order to get through the harsh, freezing temperatures of winter. If trees did not shed their leaves, their soft vegetation would certainly freeze during winter time, damaging and, no doubt, killing the tree.
In order to cope with the grueling winter temperatures, trees slowly close off the veins that carry water and nutrients to and from the leaves with a layer of new cells that form at the base of the leaf stem, protecting the limbs and body of the tree. Once the process of new cell creation is complete, water and nutrients no longer flow to and fro from the leaf - this enables the leaf to die and weaken at the stem, eventually falling gracefully to the ground.
Mother Nature treats us to a spectacular yet fleeting color show only once a year. Here’s the lowdown on why it happens and how to capture the reds, golds, and oranges in all their glory.
Leaves change color in the fall because there’s less daylight.
The reason can mainly be chalked up to the shorter days. According to the United States National Arboretum, the green pigment in leaves, called chlorophyll, is what is responsible for photosynthesis, essentially the process of converting sunlight and water into food for the tree. So as the day shortens, there is less sunlight, and hence less “food.” As a result, the chlorophyll in the leaves dies off along with its green pigment. And xanthophylls, the yellow-colored pigments, and carotenoids, which are orange-colored pigments, are now suddenly visible without the presence of the overpowering chlorophyll. The red or purple pigments, however, are produced in the autumn by anthocyanins. That’s why you’ll sometimes see tinges of red on an otherwise yellow leaf. As autumn continues, these pigments break down just as chlorophyll did—all except for the brown-colored tannins.
The weather affects color intensity.
Some years produce spectacular reds and purples, while other years are heavy with yellows and browns and pale in comparison. When a few warm, sunny autumn days and cool but frostless nights come one after the other, it's going to be a good year for the brightest reds and purples, says The Department of Forestry and Natural Resources. Plenty of rain throughout the growing season also plays a part in producing a bolder palette. If there has been a drought during the growing season, however, the leaves may fall from the trees before they even get a chance to turn colors. And if there was an early frost, leaves won’t change to red or purple at all. A lack of wind and heavy rain throughout the autumn helps to prolong the display.
There is no color code for the leafs - the color results from biochemical reactions. Basically there are three colors: Green, yellow and red.
For further reading these articles are interesting:
There is also the hypothesis around, that the bright colors are a warning sign to insects, this is called the co-evolution theory of autumn colors. The color should warn the insects that the tree has a high level of defense and thus reduce its parasitory load. You can read more about this hypothesis here:
It would be easy to use this observational, empirical information to conclude abstract illustrations and cute analogies of what we can learn from trees and leaves. You can certainly do that, but don’t miss the direct implications nature is showing us. After all, we humans are part of that nature too.
Rather than defaulting to the egocentric and thinking that all this stuff about trees is meant to help us make some insular connections about our lives, keep seeking knowledge and curiosity. Learn from the tree by taking this information to inform our perspective for how we, too, move and live in the world.
What trees are showing us is not a metaphor for something specific to our individual lives, but it’s also not disconnected from our existence. A tree is not an object that exists for us to use. Rather, a tree is a member of our existence, and if we pay attention, we can observe its function and follow suit.
When we see a landscape of oranges, yellows, and reds, are we mesmerized by the awe of being alive? Are we enraptured by seeing an authentic portrayal of the natural world we are a part of?
A beautiful fall landscape is a bunch of leaves that have given what they can and are now done, offering the visible parts of their essence as a way to mark that something is over.
And then they go and still affect the world.
Even when you can no longer see them.
Because of an etiological question from the astute phenomenology of my children, I have come to understand the world I inhabit a little bit more. It has forced me to embrace the mystery of existence in something so simple and ordinary as a tree, but it has also compelled an unforeseen recognition of the ethical map I hope to better traverse.
Knowing about trees can incarnate a better world.
Because growing like a tree is a wonderful precedent.
I think my children and I are all a bit better for understanding the world so as to better live in it.