How Do the Leaves know it’s Fall?

How do the leaves know when it is time to change colors? They obviously can’t read a calendar, so instead, they have to rely on seasonal cues to let them know that fall is here, and winter is on the way.

To understand why leaves change color during the fall, we first have to understand what makes them green in the first place. Plants make their own food through a process called photosynthesis, using ingredients like Carbon Dioxide, Water and Sunlight. But none of this would be possible, without their secret ingredient, Chlorophyll. Chlorophyll is a chemical that allows the plants to convert sunlight into energy. Chlorophyll also happens to give leaves their green color. Underneath this green, other colors are present but remain hidden until the fall season.

As the days get shorter, plants start preparing for winter. Much like a bear hibernates for winter, plants go through a hibernation phase as well. Less sunlight means less energy available for photosynthesis. In order to conserve energy during the winter months, plants stop producing chlorophyll which causes the green color to slowly fade from the leaves. In its place, hidden hues like yellow, orange and red, are finally able to take center stage.

But what makes some years autumn colors more spectacular than others? It turns out that weather plays an important role in the intensity of the fall colors. A summer drought can delay the onset of the colors, an early frost can speed them up, and a warm fall can prolong the colors but lower their intensity. The most vibrant autumn colors seem to come from years with a mild and wet spring, followed by a fall with sunny days but cool nights.

The leaves have already begun to change across Maryland, but check out the map below to see when the peak colors arrive for each area of the Northeast:

Ava Marie


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