Why Trees Shed Their Leaves in Autumn

August 20, 2018

Autumn is a favorite season for many of us here in Chicago. After all, who doesn’t appreciate the cooler weather, football-filled weekends, and pumpkin-spiced everything? These aren’t the only reasons to appreciate fall, though.

Nothing beats going on a walk and noticing all the fall foliage around the city. But have you ever wondered why trees even shed their leaves in the first place? We answer that question and more in our latest post.

Keep reading to learn more.

Why do leaves fall?

Whether you’ve lived in Chicago for one year or multiple decades, you know how bitterly cold the winters can be. Just like you might prepare your home for winter, so too does your tree. Think of a tree shedding its leaves as a way to reduce itself to its toughest parts (stem, bark, branches, and trunk).

So how do trees know when it’s time to lose their leaves? Interestingly, trees can sense when the days become shorter. Their chemical light receptions can even register day-length changes of as little as 30 minutes.

Once trees sense the loss of light, they undergo changes that produce the beautiful seasonal colors we appreciate so much.

How chlorophyll fits into the equation  

Let’s revisit middle school science class for a moment. If you remember, the green pigment known as chlorophyll is what allows plants to absorb sunlight and turn it into food that can be stored for winter dormancy.

How do trees use chlorophyll? Well, the pigment is created about as fast as the tree uses it, which is why leaves stay green throughout the summer. However, as daylight lessens, the production of chlorophyll comes to a screeching halt.

Now we can discuss why trees change color this time of year. Keep in mind that carotenoids, which produce the yellow, orange, and brown we’re accustomed to during autumn, are masked by the green pigment during the summer. Once the chlorophyll disappears, the carotenoids add a seasonal pop of color.

Carotenoids aren’t the only important pigment group, though. Anthocyanin pigments are what gives leaves a distinct red or purple color. Anthocyanins also shield the leaves from cold temperatures and allow the leaves to stay on the tree longer.

When to expect your tree’s leaves to fall

It’s hard to believe Labor Day is just a few weeks away. Before you know it, you’ll be raking and preparing your yard for cooler temperatures. So when exactly will leaves in Chicago start to fall from trees?

It depends, really. The fact is that your tree’s leaves may be damaged by insects, disease, or nasty lightning storms. As the days become shorter, the abscission layer (where leaf stem meets branch) starts to choke off the veins that move water into the leaf and food into the tree itself.

Soon after the abscission layer dries and decomposes, the leaf detaches and falls from the tree. Pretty cool, right?


We hope you can take some time these next few weeks to enjoy the fall foliage around the city. Of course, when it comes to caring for your own trees, we are here to help. Be sure to check out last year’s ‘Fall Tree Care Checklist From Pro Tree’ blog post.

Pro Tree has been serving Chicago and surrounding suburbs for nearly 40 years. During that time, we’ve figured out what works and what doesn’t in the industry.

If you’ve done any search yet for a local tree service, you know there are a number of options. The sad truth is that many tree care professionals take advantage of their customers. That’s not how we do business at Pro Tree.

You can count on us to walk you through your options and come up with a strategy that best suits your situation and budget. For example, it could be that tree trimming/pruning might make the most sense. On the other hand, perhaps tree removal is the most sensible option.

Pro Tree Service gets the job done right the first time. Why risk signing a contract with a shady or inexperienced team? See what makes us the standard in local tree care.

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