Gardening 101

Why Do Leaves Change Color?

Society is profoundly affected by autumn. Every year as the days get shorter, nights grow longer and the temperature outdoors becomes cooler, the leaves in our abundant deciduous forests across the state and country begin to turn bright hues of gold and crimson.

Millions of tourists come to visit our national and state forests every year to experience fall’s brilliance. Perhaps the warm coolers are nature’s way of warming our spirits in preparation for the cold temperatures that follow.

The changing of color in leaves is largely connected to the change in day length. As days grow shorter, photosynthesis and chlorophyll production in the leaves slow down until they eventually come to a stop. Chlorophyll is what gives leaves their green color. When chlorophyll is absent, the other pigments present inside the leaf begin to appear. These pigments are known as carotenoids. They produce colors of yellow, orange and brown.

In addition to being influenced by the change in day length, a plant’s fall color is affected by the weather and the intensity of light. Anthocyanins are red and purple pigments that are produced when excessive amounts of sugar in the leaves combine with bright light.

Scientists hypothesize that the anthocyanin pigments in leaves help to protect the photosynthetic system as plants prepare to go dormant and nutrients are being transferred to other areas of the plant. The anthocyanin pigments produced in some leaves depend largely on the pH level of the cell sap (sugar) in the leaf. Leaves with highly acidic cell sap produce very red hues, while leaves with lower pH levels produce purple hues.

The changing fall weather causes a corky membrane to develop between the branch and the leaf stem. This membrane reduces the flow of nutrients into the leaf and begins the leaf changing process, which is completed when a layer of cells at the base of each leaf is clogged, sealing the foliage from the environment and finally causing the leaf to fall.

Nature creates this magical canvas every fall, which is an inspiration to gardeners and outdoor enthusiasts. Consider incorporating a few tree specimens into your landscape that have stunning fall foliage. The United States National Arboretum has a wonderful list of plants with fall foliage colors that range from yellow to brilliant red. Visit www.usna.usda.gov/PhotoGallery/FallFoliage/FallColorList.html. To find more information on planting trees and shrubs in North Carolina, visit www.ces.ncsu.edu/depts/hort/hil/hil-601.html.

Byline:

Michelle Wallace is the Consumer Horticulture Agent for the N.C. Cooperative Extension Service in Durham Co. If you have general garden questions, contact the Durham Extension Master Gardeners at 919-560-0528 or email mastergardener@co.durham.nc.us.