Fall Leaves: Why Do Leaves Change Color?

Learn What Makes Fall Foliage so Brilliant and Bright!

By George and Becky Lohmiller
September 16, 2020
Red Oak Leaves

Ever wonder why leaves change color? Did you know that fall’s vivid colors are actually hidden underneath summer’s green? The main reason for color change is not autumn’s chilly weather, but light—or rather, the lack of it.

Why Do Leaves Change Color?

First of all, not all leaves turn vivid colors in the fall. Only a few of our many species of deciduous trees—notably maple, aspen, birch, oak, and gum—produce truly stellar performances for our annual autumn spectacular in North America.

Several factors contribute to fall color (temperature, precipitation, soil moisture), but the main agent is light, or actually the lack of it. The amount of daylight relates to the timing of the autumnal equinox, when day and night are roughly equal, but nights are growing longer.

As the autumn days grow shorter, the reduced light starts chemical changes in deciduous plants, causing a corky wall of cells (called the “abscission zone”) to form between the twig and the leaf stalk. This corky wall eventually causes the leaf to drop off in the breeze.

As the corky cells multiply, they begin to seal off the vessels that supply the leaf with nutrients and water and also block the exit vessels to some extent, trapping simple sugars in the leaves. The combination of reduced light, lack of nutrients, and less water triggers the trees to start the process of breaking down the pigment chlorophyll, which contains valuable nutrients and is the source of the “green” in leaves. As chlorophyll is broken down and the green color fades, yellows and reds are revealed.

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Where Do the Bright Yellow and Red Colors Come From?

Once the green chlorophyll is gone, other pigments begin to reveal their bright faces. These pigments, carotenoids (yellow) and anthocyanins (red), are responsible for the lovely colors of fall.

Yellow carotenoids exist in the leaf all summer, but are masked by chlorophyll during the growing season. Red anthocyanins, on the other hand, are freshly produced by plants as fall conditions ramp up. Suprisingly enough, scientists aren’t enitirely sure why trees bother to produce a new pigment while otherwise trying to save their precious resources for the winter ahead. Some suggest that the bright red color could deter insect pests from feeding on leaves, or that red attracts birds that feed on (and spread) the trees’ fruit. 

However, another interesting theory is that the red pigment acts as a sort of sunscreen for the leaves, staving off damage from bright autumn sunlight and allowing the leaves to stay on the tree for longer than they would if they were to remain green or even yellow. 

Sugar trapped in autumn leaves by the corky wall is largely responsible for the vividness of the colors. Some additional anthocyanins are also manufactured by sunlight acting on the trapped sugar. This is why fall foliage is so sparkling after several bright fall days and more muted during rainy spells.

Finally, as autumn carries on, leaves begin to turn brown once all their nutrients are re-absorbed by the tree. The brown color is the result of the leftover tannins, a chemical that exists in many leaves, especially oaks.

What Weather Conditions Bring the Best Fall Foliage?

In general, a wet growing season followed by an autumn with lots of sunny days, dry weather, and cold, frostless nights will produce the most vibrant palette of fall colors. This vividness is especially true of red leaves, such as those on sugar maples and red maple trees.

Check your long range forecast to see whether a dry autumn is in your future.

Of course, if freezing temperatures and a hard frost hit, it can kill the process within the leaf and lead to poor fall color. Check the frost dates in your area!

Also, drought conditions during late summer and early fall can trigger an early “shutdown” of trees as they prepare for winter, causing leaves to fall early from trees without reaching their full color potential.

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Where Can You Find the Most Beautiful Fall Foliage?

Does your area experience fall foliage? Some level of autumn foliage changes in most regions of North America, but it’s New England, the upper Midwest, the Rocky Mountains, and parts of the Appalachians that hold the jackpot for leaf peepers. The right climate and light conditions and an abundance of the tree varieties that hoard colorful pigments come together in these places.

While tradition has it that Columbus Day weekend is when the color peaks in New England, the mythical maximum occurs in northern Maine in mid- to late September and “travels” south, reaching the Connecticut shore by late October. 

When to Look for Fall Leaves

Wondering when the leaves will change in your area? Below is an animation of the changing leaves from past years, based on the foliage reports from our readers. Although every year is different, this map should give you an idea of when leaves typically start to change across the country.

Animated Map for 2019 Foliage Reports

Are the leaves starting to fall in your garden? Find out how to do fall clean-up right, then what to do with fall leaves!

How are the fall leaves looking in your area? Let us know below! We hope you have a beautiful autumn.

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Reader Comments

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Wedding in Ohio

I'm planning a fall wedding in Ohio. Right now we are thinking October 12th of 2019, do you think we will have any fall foliage at that point? Do you know when the 2019 Fall Foliage guide will be posted?

I'm planning a fall wedding

I'm planning a fall wedding in 2017 in Niagara Falls, ON. The dates available are Sept 30 and Oct 28. For best chance of changed coloured leaves with some on the ground, which date would you suggest?

Hmm. You might call Niagara

The Editors's picture

Hmm. You might call Niagara Parks in Ontario for their recommendation. In general, it looks like the mid to late October is the peak in that region, the display being delayed by the warmer water and microclimate (according to the Niagara Falls State Park on the U.S. side), but that can vary each year depending on various factors.

The following site from Yankee Magazine offers a live fall foliage map which extends to the Niagara Falls area on the U.S. border. As of November 11, for example, the area around Buffalo, New York is reporting still at peak, but a tiny bit north, along the shore of Lake Ontario, the fall foliage display has ended.  [Here in southeastern NH, at elevation 1,440 feet, on November 11, most leaves have fallen, but there are a few trees still clinging on to their leaves, in russets, browns, and a few deep golds. Most reds, bright oranges, and yellows are gone.]

https://newengland.com/seasons/fall/foliage/live-fall-foliage-map/

My guess is that September 30 would show a few spots of color on some trees, but the color display would not be in full gear yet, and not many leaves on the ground (and not many bare branches). However, October 28, you might be past peak, with many leaves on the ground and perhaps not as many colorful leaves still on the trees.

For more information, you might be interested in the following:

https://newengland.com/category/seasons/fall/
https://newengland.com/today/seasons/fall/weekend-foliage-planner-new-en...

There are several webcams of Niagara Falls  – you might check them for an idea of what November looks like there, to give you an idea of late October, perhaps.

Hope this helps!

My birch trees...

My back yard has a foot of leaves from my eight birch trees that have been dropped over the last two weeks. I've lived just outside of Andrew's Air Force Base in Maryland for 30 years and don't remember the leaves dropping this early before now. Elderly so maybe a faulty memory?

Nevertheless, can you tell me if this is due to our odd weather or are my trees in danger? As would be my house if this means they are sick or dying...

Thanking you in advance for whatever help you can give.
Dorothy

birch leaf drop

The Editors's picture

We can not be absolutely certain whether the leaves of your birch trees are falling on schedule or not; there are too many factors involved. Nor do we know if your trees are in danger, however, we can tell you signs to look for:

• do the leaves have spots? This could be an indication of fungal disease or insect feeding.

• drought stress can cause leaves to turn yellow and drop. Drought has been a problem in a lot of places.

• it’s possible that your birches have an iron deficiency. This stems (no pun intended) from poor soil—poor in terms of what the tree needs. Soil that is too alkaline for iron to be available to the tree can be a problem. Adding iron sulphite can help. But get a soil test before you add anything.

• Finally, look around the neighborhood or area for trees like yours (with or without their leaves). If they have not dropped their leaves, see if the owner can share his care tips and ideas. If the trees have dropped their leaves, do the same. At least this way you will have a better sense of this is a singular problem for you or if other birches are “acting” the same way.

We hope this helps!

Thank you for this

Thank you for this *intelligent* article on autumn foliage!! I was born and lived in New England (70 yrs. ago) but at the age of 22 left to live in NORWAY. I have all these 48 yrs. missed the beautiful New England fall colors 'the Almanac Staff' mentions as being just about the brightest in the US. Do yo have any *almanac* friends in Norway that can enlighten me/us as to why I see so little of those gorgeous REDS here. I have rightfully understood throughout the years that soil, rainy/foggy autumns, amount of light/length of days (we have an early dark period as opposed to the well-known long sunny/light days of summer); and we get very early winters (lasting so long as to give us approx. 2 mos. each of the other 3 seasons many places in Norway!)...

For the past 7 years I have lived in the mountainous valley called Sigdal, and I see (as you may well suspect) only a few reds among our most common deciduous trees: Aspen (though rather often in just a yellow-orange frock), Mt. ash (a native rowan, in particular the 'European Sorbus aucuparia'--also in variations of colors, not always red), some maples (but not many and perhaps a different 'variety' than we had in New England??--maybe with far less 'sugar content'? that tend to be orange more than deep red)...Can you suggest a good link on this subject or tell us if what I experience here in the county of Buskerud, Norway IS very different to New England--and for what reasons. Grateful if I receive an answer...Thank you!!

Enjoyed your article. I knew

Enjoyed your article. I knew some of this, but it clearly explained the stuff I hadn't.

There is a little typo in the article. In the first sentence after the last photo it reads "within the leaf an dlead to poor fall color" when you meant "within the leaf and lead to poor fall color."

Normally I blow right through these but the word "dlead" made my brain come to a full stop and try and figure it out.

Thank you, Paul! We

The Editors's picture

Thank you, Paul! We appreciate the time that you took to mention this—and your interest in The Old Farmer's Almanac and our Web site!

I can generally get a good

I can generally get a good handle on how hard and cold the winter is going to be in NJ by when my horses start to get their winter coats and how thick they are. If they start early and are thick, you can bet we are in for a cold winter.

Interesting comment,sounds

Interesting comment,sounds like something my brother would say about his horse's.
don't know why, but I have always been afraid of them.

The leaves here in Western,NY

The leaves here in Western,NY are beatiful this year.The best I have ever seen in 30+ years I have lived here.

The true fall will not come

The true fall will not come until after the election, and that will be whoever lost it--has "fallen".

Our foliage typically doesent

Our foliage typically doesent peak until October. Im getting very impatient for the arrival of autumn. September is still summer and you wont have that true fall feel until October, when the days grow very short, gets chilly at night, colorful light shows, my yard is covered in white by the first frost and that cool crisp air in the daytime. Ahhh it makes one dream! but its only 22 more days, I think i can make it. Will Virginia see a good light show too? its been too hot this past summer! im looking foward into seeing leaves fall through the chilly breezes

Will our dry summer effect

Will our dry summer effect the colors of the autumn leaves?

In general, dry weather

The Editors's picture

In general, dry weather produces the most-vibrant color. So, that's one positive effect of no rain!

Plus it makes the leaves

Plus it makes the leaves crunch!!