Why Do Leaves Change Colors and Fall Off Trees?

What Happens to plants in the Fall? 

As summer fades into fall, the days grow shorter, and there’s less sunlight available for photosynthesis.  

Trees begin to sense this change and start preparing for winter. They no longer need to produce as much food, so they stop making chlorophyll.  

As the green color fades, the other pigments that have been hiding under the surface all along begin to shine through. Carotenoids give us those beautiful yellows and oranges. These pigments are always present in the leaf but are masked by the green chlorophyll during the warmer months. Anthocyanins bring out the brilliant reds and purples. These pigments form in the fall, created when sugars get trapped in the leaf and react with sunlight. 

As chlorophyll breaks down, the tree is also conserving energy and nutrients by reabsorbing them from the leaves. This way, the tree can store them in its branches and trunk to use when the growing season starts again in spring. 

How Do Trees Prepare for Winter?

As beautiful as fall foliage is, it’s not just for show—it’s a key part of a tree’s adaptation strategy. Trees shed their leaves to survive the harsh conditions of winter.  

During winter, the ground often freezes, making it hard for trees to take up water through their roots. By shedding leaves, trees reduce water loss. Without leaves, they can conserve moisture and avoid drying out when water is scarce. 

Leaves are delicate and vulnerable to frost damage. If trees kept their leaves during winter, ice could form on them, causing the branches to break under the weight of snow or ice. Dropping leaves helps protect the tree from winter storms. 

Many trees go into a kind of “hibernation” in the winter, called dormancy. By slowing down their metabolic processes and shedding leaves, they conserve energy during the cold months, only to “wake up” again when conditions are favorable in spring. 

This seasonal cycle of growth, adaptation, and rest helps trees survive and thrive year after year, making them masters of resilience in the natural world. 

Why Do Different Trees Turn Different Colors?

Not all trees shed their leaves the same way, and that’s why we see a rainbow of colors each fall. The type of pigments each tree produces, combined with environmental factors like sunlight and temperature, determines which colors emerge. 

Maples produce high levels of anthocyanins, giving them their signature fiery reds. 

Oaks tend to turn brown or russet, as they don’t produce as much anthocyanin. 

Birches and poplars turn yellow because they have carotenoids, but less anthocyanin to give them reds or purples.

Tracking Washington State’s Fall Foliage

Many areas of western Washington are already starting to show hints of fall color, but the best is yet to come! According to smokymountains.com, peak fall foliage is expected to appear later in the year compared to 2023. 

King County is expected to reach its peak color around October 21, while Whatcom, Skagit, Thurston, and Clallam Counties are predicted to hit their peak about a week earlier, around October 14. 

Last year, King County’s fall colors were forecasted to peak around October 2, so we’re seeing a later shift in timing this season. 

If you want to plan the perfect autumn hike or scenic drive, this foliage map can help you time it just right to catch the brightest and most vibrant colors Washington has to offer.  

Where can I take a fall foliage hike in Washington state?

Now that you know why leaves change color and how trees adapt, why not explore the beauty of fall in action? Autumn is the perfect time for a family hike to observe these changes up close. 

Here are a few great spots in Washington to see stunning fall foliage and learn about tree adaptations… 

• Twin Falls Trail (North Bend). This family-friendly hike offers views of trees shedding their green and turning brilliant shades of yellow and orange along the Snoqualmie River. 

• Mount Rainier National Park. Known for its breathtaking fall landscapes, this park offers a mix of evergreen and deciduous trees, giving a colorful contrast to the scenery. 

• Washington Park Arboretum (Seattle). For an easy walk, head to the Arboretum and enjoy the variety of trees, each adapting to fall in its own way. Take time to spot the differences between trees preparing for winter. 

As you walk, ask questions like, “What colors do you see?” and “Why do you think this tree is losing its leaves?” It’s a fun way to connect science with the natural world and learn more about the survival strategies of trees. 

about the author

Emily Jeung is a passionate marketing and communications professional based in Seattle, working at Pacific Science Center. Specializing in engaging content creation and strategic outreach, Emily is dedicated to enhancing the center’s mission of delivering impactful science education and fostering community connections. When she isn’t working, she enjoys exploring the outdoors, crafting, and cooking.

Email Emily for insights and collaboration opportunities.