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When Do The Leaves Change Color?


photo taken on September 18, 2014  from the Jud Wiebe Trail

Guests often ask “What is your favorite time of year in Telluride?” Although a cobalt blue summer day with abundant wildflowers or a blue bird powder day with a foot of fresh are hard to beat, a glorious fall day could take the number one spot. 

There is something magical about fall in Telluride. The aspen leaves ablaze in yellow and orange shimmer in the trees until a gentle breeze makes them float and dance gently to ground. This beautiful act of mother nature creates  the illusion of raining drops of gold which transform many of Telluride’s trails into a mountain version of “the yellow brick road.” 

A popular question in the fall is “When do the leaves turn color?” This is difficult to answer as it varies from year to year. Generally the leaves start to change in mid-September, peaking the last week of September and falling off by the second week in October, but again this timing can vary quite a bit. 

Our weather has been glorious lately with warm sunny days and crisp nights (the ideal conditions to bring out the maximum color) so a spectacular display of fall colors should be just around the corner. 

A few groves of Aspens have started to change (as seen in the photo above) but we anticipate the Peak of gold season to be at least two weeks away. Tune into this blog weekly as we will keep all the leaf peepers informed and up to speed on the status of the color change. 

Here is some helpful information from the US Forest Service that sheds some light on "Why leaves change color" so we can better predict "When the leaves change color."

How does autumn color happen?

Three factors influence autumn leaf color-leaf pigments, length of night and weather, but not quite in the way we think. The timing of color change and leaf fall are primarily regulated by the calendar, that is, the increasing length of night. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with Nature's autumn palette.

During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors of orange, red and yellow.

How does weather affect autumn color?

The amount and brilliance of the colors that develop in any particular autumn season are related to weather conditions that occur before and during the time the chlorophyll in the leaves is dwindling. Temperature and moisture are the main influences.

A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. 

The amount of moisture in the soil also affects autumn colors. Like the weather, soil moisture varies greatly from year to year. The countless combinations of these two highly variable factors assure that no two autumns can be exactly alike. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.

In early autumn, in response to the shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.


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