Why do leaves change color?

Weather

ALBANY, N.Y. (NEWS10) — Have you ever wondered why the leaves change color from green to those vibrant, yellows, oranges, and reds in autumn? A lot of the science behind the changes has to do with the angle of the sun and how much sunlight the trees are able to “consume” for food.

You will typically see us beginning to show the “Foliage Report” as early as the middle to end of September, this is where we highlight the best areas that are showing the best colors for that upcoming week. Below is an example from the week of October 7 through October 11:

But why do the leaves change? During the warmer months, we see leaves as green, however, all leaves also have orange and yellow pigments within them, we only see the green color thanks to the dominance of chlorophyll that is present in the leaves. As we get into the cooler months, what we typically refer to as fall, chlorophyll production comes to an end and the other pigments within the leaves are revealed, that is when we start to see the beautiful fall foliage.

During the growing months, we of course see more sunlight, along with warmer temperatures and rain. All these factors help to keep the leaves healthy and green. This is thanks to the chlorophyll that helps to trap the sunlight in the leaves and creates the food that helps the tree grow during the season.

After the summer solstice, we slowly begin to lose daylight as the sun goes lower on the horizon. We don’t notice it at first, but as we go later into September and October it is more noticeable, relatively longer nights and shorter days. The intensity of the sunlight continues to decrease during this time frame and this leads to the initialization of the color change.

Spongy cells begin to form in the stem of the leaves. This blocks the transport of water from the tree trunk and branches to the leaves. Once the fluid transfer stops, that is when chlorophyll stops being produced and the other colors present in the leaves begin to peek out.

Sugar becomes trapped in the leaves and the other yellow, orange, and red pigments start to become more visible.

But the weather leading up to the onset of the change has an impact on what colors the leaves will become. Leaf change may be muted and perhaps even delayed by 1-2 weeks if the weather has been much drier than normal. On the flip side, a wetter than normal lead-up to foliage season will provide on-time leaf change along with perhaps a more vibrant display of foliage.

Temperatures also play an impact on what we will see come foliage season. A warmer lead-up to foliage season with more clouds, warm days, and warm nights will typically showcase a more muted color showing. However, when we start to see cooler weather with seasonally warm days, more sun, and those cool crisp nights then the display of colors is typically more vibrant.

Here are some of the colors that you could see on the different species of trees, whether they be in the Capital Region or elsewhere, some of them sure know how to put on a show! Bottom line, we are approaching peak foliage here in the Hudson Valley, it is a touch late this year, but it is looking likely that in the next one to two weeks, we will be at peak. Take advantage of the milder weather and go check out those colors!

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