Why do leaves change color in fall?
Have you ever wondered why leaves change color in the fall? Different cultures have answered this question in their own way. One folktale is that Jack Frost leaves beautiful patterns on the autumn leaves to mark his passing. Native American legends attribute the autumn leaf color to the when the constellation Great Bear was killed by spirit hunters in the sky, his blood rained down covering the forest changing its leaves to red.
Now we know through science that neither tale is true but it is no less as magical that many trees change colors in autumn to create a visual tapestry across our land.To understand what happens in the fall we must look at the spring and summer when leaves make food for the tree through photosynthesis. This takes place in the leaf cells that contain the green pigment called chlorophyll. Chlorophyll makes the leaves look green but it also does most of the work to turn sunlight into sugars. Simply during the warm temperatures and the long days many of our plants are green. So now we know why they are green but what causes the different colors in the fall?
In the fall due to the changes in daylight and temperature chlorophyll breaks down and the green color disappears, replaced by other pigments. The leaves changing to yellow, red, orange or brown are from pigments called carotene. The bright yellow of daffodils, orange of carrots and the red of tomatoes are from carotene. The leaves that are red, wine-red, purple or blue come from pigments called anthocyanins, which make cherries red and cabbage purple. These pigments determine the shades of autumn color.
Shorter days & cooler nights truly create a magical time when trees receive nature’s messages to stop producing food. Sugars that are left the tree draws back through the leaves to the stems and on through to the roots. This is how trees economize their food resources during the winter. So in the last act of this spectacular play we finally find out how leaves change their color. It happens when as we stated before the last of the chlorophyll degrades and the green color begins to fade. At this time the leaf slowly prepares to let go of the limb, which triggers the veins in the leaf to narrow trapping the last bit of sugars and pigments in the leaf finally changing the leaves to autumn colors.
With all of that going on in a simple leaf you would think the colors would be the same every year but they’re not. As with all plants it is affected by soil moisture, day & night temperatures, sunlight and rain. Oh and don’t forget that each variety can react differently to each change. One plant may have more color with more rain another may have less. A warm wet summer may delay fall for weeks or as we have seen many times a hot dry summer can make the leaves change and drop early.
Some of you may look at fall leaves as a back breaking chore to bag and put on the curb. This year think of the simple miracle that leaf gave you and thank it by creating a compost pile or getting a mulching lawn mower to feed your trees so they can use those leaves as fertilizer to begin the whole process over in the spring.
