The Chemistry of Fall Color
Everyone knows that chlorophyll, produced by photosynthesis, gives plants their green color during the spring and summer. You might not know what causes the vivid reds, oranges and yellows that appear in the fall.
When plants are actively growing, they produce and break down a lot of chlorophyll. It sounds strange, but the same sunlight that causes plants to produce chlorophyll also breaks it down (as do cold weather and short days). Somehow this balances out, with the plant being able to produce enough carbohydrates to grow, flower and fruit.
Carotene absorbs blue-green and blue light, causing yellow to reflect. During active growth, chlorophyll is produced in such quantity as to cover the other color causing chemicals. Carotene is a stable substance that assists with photosynthesis and remains in the leaves after shorter, colder days cause the chlorophyll to break down and not be replenished.
Anthocyanins absorb blue-green, blue and green light, causing red to reflect. These chemicals occur in the sap of the plant and may show as red or purple, depending on the pH of the sap. They are also masked by chlorophyll during the growing season.
Different plants contain more or less carotene and anthocyanins to produce yellow and purple and every imaginable shade in between. You can be sure that the dogwoods that produce brilliant purple leaves contain a great deal of anthocyanins and very little carotene. Freezing temperatures are the enemy of bright fall reds, as they reduce the formation of anthocyanins, so be sure to get out there and enjoy the color now!