Changing Leaves

Outdoors

By: Jacob Williams, UGA Extension Agent for Towns and Union County

This time of year you’ll see leaves start to change colors. In the mountains the colors can make a
beautiful sight. But why don’t evergreens lose their leaves, and why are there all the different colors?
Let’s talk about it so that as the leaves change this year you can show off your scientific knowledge to
your friends!

Firstly, leaves can change color for a variety of reason. Disease, drought, nutrient deficiency among
other things are all reasons why leaves can change colors. In the plants cells there is a chemical called
chlorophyll. Chlorophyll is crucial to the plant. Chlorophyll converts the light energy into chemical
energy in a process called photosynthesis. That chemical energy is used by the plant for growth and
reproduction. If you eat a plant then you’re ingesting that energy too. If you eat an animal that has been
eating plants you’re still ingesting that energy. Photosynthesis is an amazing process that is one of the
biggest building blocks of life.

The chlorophyll can absorb many wavelengths of light. However, the green wavelengths are not
absorbed but reflected. This gives leaves the green color that we see. Next to the chlorophyll in the
plant leaves there are other chemicals that serve as a buffer to protect the chlorophyll. These other
chemicals are pigments and they absorb the wavelengths of light that would be dangerous to the
chlorophyll. These pigments vary in the color that they reflect from yellow to orange.

As the temperature starts to drop and the days get shorter, chlorophyll will start to break down in the
leaves and stop converting light energy to chemical energy. During the growing season, there is so much
chlorophyll in the leaves that the green color overpowers the pigments yellow to orange. However, with
the chlorophyll beginning to break down the pigment’s coloring begins to show through. Different
species of plants will have different levels of chlorophyll. The mixing of chlorophyll and pigment will
result in the different colors of leaves that we see in the fall. The weather can affect the intensity of the
leaf color. Colors will be more intense with rainy and overcast days.

While the leaves are changing color the tree will also begin to create a special layer of cells at the point
of attachment for the leaf to the tree. This layer of cells will seal the tree off from the leaf so that an
open wound is not left when the leaf falls by its own weight.

Not all trees lose their leaves in the fall. Evergreens such as pines, hemlocks, and firs to name a few have
a thicker coating of wax around their leaves. All leaves have a thin coating of wax that is used to protect
them from drying out. On evergreen trees, the wax coating is thicker and can protect the leaves through
the winter. Evergreens will still lose leaves, but they don’t lose them all at one time. They’ll completely
replace all of their leaves over a period of 2-4 years.

If you have agricultural questions or please contact your local county Extension Office. You can also send
me an email at Jacob.Williams@uga.edu. Enjoy the leaves this fall!

Towns and Union County Extension are having a Master Gardeners training course that will begin January
29 th . This is a 10 week course that will teach about horticultural practices and includes volunteer
opportunities. The cost is $175. Contact your local Extension office for more information or email me at
Jacob.Williams@uga.edu.

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