Well, its been a fabulous summer, full of plenty of hot days, high water bills and forest fire smoke. (translated: suntans, nice green grass and beautiful sunsets). Those of you who suffer from Seasonal Affective Disorder are getting out your light therapy lamps or booking that tropical vacation as days grow short and the gloom settles in. Living in the northwest for any length of time will quickly condition you to hang on loosely to our short little summers and try not to fly into Fall, kicking and screaming. Alas, there is a small consolation (besides your kids getting on a bus every morning), as you peer across your withering landscape: Fall color.
That fleeting transition as long cool nights and short days send a signal to plant life that it’s time to start closing up shop. Chlorophyll cells in the leaf, no longer needed, begin breaking down, revealing remaining cells which can be red, yellow or brown or all hues in between.
On the west side of the Cascades, we have a plethora of deciduous tree and shrub species displaying the spectrum of fall colors, starting in late September. On the east side of the mountains, Tamarack and Aspen start turning gold even sooner. Some years are more dramatic than others. Dry, still weather in fall is conducive to more brilliant color whereas wet, windy weather shortens the window for bright color to develop and causes leaves to drop sooner.
Here is a great website explaining the chemistry behind fall leaf color and senescence: