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It's Fall, but why are the leaves still green?

Most leaves remain green despite being in the second week of October. What factors determine when leaves change color?

Posted: Oct 8, 2018 6:18 PM

WEST LAFAYETTE, Ind. (WLFI) - Fall may be in full swing, but one piece seems to be missing. Most leaves remain green despite being in the second week of October.

The green color we see is created by chlorophyll. The cells help convert sunlight into glucose which feeds the trees.

Temperatures are important in determining how long leaves remain green. Warmer temperatures allow for more glucose to reach the leaves. This will keep then green for longer periods. “If it's dry and warm, then what happens is the trees are still working and we don't get the fall color we want,” said Purdue Urban Forestry Specialist Lindsey Purcell.

“The mini drought that we had for about two or three weeks where we had hot temperatures and no rain might have a negative effect on our fall colors,” added Purcell.

There are three main factors driving when leaves change color.

First, we have soil moisture. This measures how much water is in the soil. If more moisture is present, trees will have an adequate water supply to continue to grow. If an area is in a drought, less water will be present. This can cause trees to go into an early dormant stage so they can survive with limited water. As a result, they often start dropping green leaves before the turn to a different color.

Second is daylight. The amount of daylight limits how much sunlight can be converted into glucose each day. The less daylight, the less photosynthetic processes occur.

Temperatures are the last key factor. Once temperatures cool, leaves are restricted from being able to receive as much glucose. In turn, leaves will begin to change colors as different biochemical processes begin within the leaves.

Leaves will show a gradual change of color during the warm weather. More rapid changes can be expected once temperatures begin to cool.

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