Pat Munts: Chemistry sparks change from green to fall colors

Fall is gently sneaking up on us. While we haven’t had a killing frost yet in most areas, seemingly ordinary trees and shrubs are suddenly turning into fiery torches and candles throughout the landscape. But how does a plant do such a complete about-face and change from green to such vivid shades of gold, red, yellow and even purple?

The change from green to the colorful shades of fall involves a little chemistry in the presence of cold weather and decreasing daylight as the sun moves past the fall equinox. All plants contain chlorophyll, a green pigment that uses sunlight to make sugars and starches through the process of photosynthesis. The plants then use them to grow, which is why it dominates during the spring and summer growing seasons.

With the onset of shorter days and colder temperatures, the chlorophyll and its green color disappear from the leaves and reveal the underlying yellow, gold, orange and brown pigments that were masked by the chlorophyll. Each pigment interacts with sugars trapped in the leaf to produce different intensities of color. Because the plants in our region produce a different level of sugars and have lower levels of purple, blue and deep red pigments in their leaves, we do not get the blazing colors found in New England. But we do have better fall color than Western Washington because of our colder temperatures.

Walking is probably the best way to savor all the color and earthy smells of the fall and save up their memory for the cold snowy days ahead. In Spokane and Coeur d’Alene, almost any neighborhood has trees to be appreciated on short walks. Some classic places are Manito Park and the Finch Arboretum in Spokane. Here both native and introduced trees put on a show that reveals the range of colors that are possible. College campuses including Washington State University in Pullman, Eastern Washington University in Cheney, Gonzaga and Whitworth in Spokane and North Idaho College in Coeur d’Alene all have wonderful displays.

If a weekend drive is more to your liking, try heading almost anywhere east or north of Spokane and Coeur d’Alene. In particular, check out Highway 20 between Colville and the Pend Oreille Valley or over Sherman Pass to Republic for outstanding displays. These drives will get you out in our native forests of conifers and deciduous trees. Birches and cottonwoods will be turning bright yellows along the lowlands near streams. Higher up, the yellows and reds of vine maple and a myriad of shrubs will color the hillsides. It is here too that you will find the tamarack or larch, one of our few conifers that changes color and sheds its needles. Each fall, trees’ needles turn bright yellow, making them stand out like candles amongst the dark green pines and firs.

Pat Munts is co-author, with Susan Mulvihill, of the “Northwest Gardener’s Handbook.” Munts can be reached at pat@inland nwgardening.com.