Fall officially arrived in Idaho a week ago, and we’ve been enjoying seeing the pictures you’ve been posting on social media of all the beautiful colors in the trees and shrubs.

It is a pretty time of year, but have you ever wondered just what makes those leaves change from green to brilliant reds and oranges and yellows?

Today on “You Can Grow It”, our meteorologist and garden master Jim Duthie explains how it happens, and he says it’s just a little more complex than you might think.

Fall is officially here, even though temperatures have been pushing 90 degrees this week. But Mother Nature has started putting on her annual display of colored leaves on trees and shrubs from the mountains to the valleys. And while cooler weather brings out our sweaters and jackets, it’s something else that triggers the changes in the leaves.

During the longer days of spring and summer, the lush green leaves on the trees act as food factories for the trees. As the trees take up water through their roots, the leaves take in carbon dioxide from the air.

Using a process called photosynthesis, the trees turn water and carbon dioxide into oxygen and glucose and starches. The glucose is a kind of sugar that the trees use as food to fuel their growth from season to season.

Inside the leaves is an extraordinary chemical called chlorophyll. The chlorophyll gives the leaves their green color, and helps make photosynthesis happen.

As summer ends and we head into fall, the days get shorter and shorter, and the trees know it’s time to get ready for winter.

During the winter, the days are shorter, and there isn’t enough water and sunlight available for photosynthesis, so the trees shut down their food production and go dormant, sleeping through the winter and living off the food they stored during the summer.

As we head into fall, photosynthesis slows down, food production in the leaves stops, and the green chlorophyll begins to disappear from the leaves.

As the green fades away, other pigments start to emerge, including the carotenoids, and we start to see the reds and oranges and yellows that were in the leaves all the time. They were just covered up by the green chlorophyll.

In some trees, like maples, some of the glucose, or sugar, is trapped in the leaves, and turns red.

In other trees, like oaks, the leaves turn brown, which is leftover waste in the leaves.

Temperature and rainfall doesn’t directly affect leaf color, but it does have an impact on the duration of the fall colors.

Wet weather tends to increase the intensity of fall colors.

But an early hard freeze will often cause leaves to drop before they completely reach their colorful peak.

So when these colors start to change, enjoy it, because it doesn’t last for long.

You don’t have to go very far to see spectacular fall foliage. In the coming weeks, you can drive down almost any neighborhood street, walk along the Greenbelt, and visit almost any park in the Treasure Valley, and find a palette of fall colors of reds, oranges, yellows and browns. It’s also a good time to shop for new trees for your home landscape, so you can see how colorful they’ll be when they’re growing in your own yard.

Fall colors are peaking in the mountains now into mid-October, and will peak in the Treasure Valley through mid-October and early November.

Here is a list of some scenic drives you can take this fall to see the best colors.


ID 55 from Boise to McCall. Alongside the spectacular Payette River, watch for the yellows and golds of aspens, western larch, and tamaracks, against the dark green of the pines.

ID 21 from Boise to Idaho City to Lowman to Stanley. Reds and golds of willows and shrubs give way to the yellows and golds of aspen through the forests along the South Fork of the Payette River, then on into Stanley Basin.

ID 75 from Shoshone to Sun Valley to Stanley. Yellows and golds of cottonwoods along the Big Wood River mixed with reds and yellows of the willows. Be sure to check out Adam’s Gulch north of Ketchum. Crossing Galena Summit, aspens mix with the pines on into the Stanley Basin.

This is a back country route, so it is mostly dirt roads with no services, so plan accordingly. But you’ll be rewarded with spectacular scenery, and lots of gorgeous golden cottonwoods and aspens amidst the rugged beauty of the Owyhee canyon lands. Portals are at either Grandview (ID 78) or Jordan Valley, OR (US 95).

Turn off ID 78 at Murphy. Again, it’s a dirt road to Silver City in the Owyhees. You’ll see brilliant yellows and golds of cottonwoods and Aspens with some pines.