Why Do Leaves Fall off Trees in Autumn?

Why do leaves fall off trees in autumn? Every gardening enthusiast, or anyone with a keen eye for Mother Nature’s whims, has likely contemplated this very question. It’s easy to dismiss this phenomenon as a mere seasonal quirk, but there’s actually a fascinating science behind it. 

As the go-to certified arborist in Pearland, our team at Country Trees LLC knows a thing or two about the intricate dance between trees and their foliage. Keep reading as we break down the nitty-gritty details of this arboreal mystery!

why do leaves fall off trees in autumn

Preparing for the Cold Months

Typical broadleaf or deciduous trees have tender leaf cells with very thin fluid flowing through them, making them particularly susceptible to freeze damage. Instead of wasting precious energy to maintain these delicate structures through the harsh winter, deciduous trees make a smart move. They undergo a radical transformation where they pare down to their most robust parts: the stems, trunk, and branches. This structural backbone can easily weather the coming season’s harshest onslaughts. 

So, how do plants know when it’s time to change their foliage color and finally shed their leaves? Well, they can actually sense winter’s shortening daylight hours using chemical receptors called phytochrome (red light detectors) and cryptochrome (blue light detectors). This precise system registers day-length changes of as little as a half-hour.

What About Evergreens?

Why do leaves fall off trees in autumn while others retain lush foliage? Evergreen varieties sport a different strategy. Their leaves, often needle-like or scaled, possess a tough, waxy coating and special anti-freeze compounds. This adaptability allows them to resist the biting frosts and maintain photosynthesis year-round. In other words, evergreens are the tenacious all-weather warriors of the plant kingdom, braving the cold while still keeping their green wardrobe.

The Science Behind the Colors

Aside from other factors like poor health, why does a tree’s foliage change color before finally dropping? Here’s a rundown of the autumnal leaf pigments and their roles.


You might think the vibrant reds, oranges, and yellows of fall just magically appear as the days grow shorter. Well, not quite. These hues are actually always present but masked by a powerful pigment called chlorophyll, the element responsible for a leaf’s green color and vital in photosynthesis. Since colder temperatures and lower light levels make the food production process inefficient, trees choose to cease the creation of chlorophyll, revealing the bright colors underneath.


When chlorophyll takes a backseat, carotenoids reveal themselves, painting the leaves with yellow, orange, and brown hues. They are the year-round accessories of leaves, playing a vital supporting role in photosynthesis by capturing energy and preventing excess light damage.


Anthocyanins are late bloomers and aren’t usually present in leaves year-round like carotenoids. They arrive on the scene in autumn, triggered by cooler temperatures, to produce a riot of reds, purples, and crimsons. These pigments help lower a leaf’s freezing point, helping it endure the biting cold and produce food for a bit longer.

How Leaves Fall

In the grand finale of autumn, the leaf drop process begins. Trees start producing cells for an “abscission layer” at the base of the leaf stems, gradually severing the connection to the main structure. 

After completely disconnecting, the leaves gradually become dry and flaky, and thanks to a nudge from the wind or a rain shower, they finally fall to the ground. This process reduces water loss and potential winter damage, allowing the tree to hibernate until warmer months.

Need Expert Assistance?

We hope we’ve thoroughly answered your concern, “Why do leaves fall off trees in autumn?” If your tree is shedding bark or its foliage has dropped prematurely, our crew at Country Trees LLC can come to the rescue — so dial 979-824-0325 today!

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