How do leaves know when to change color?

In the fall, days start to get much shorter and the nights start to get longer. Plants no longer get the amount of sunlight and water necessary to produce energy so it won't need its leaves or chlorophyll any longer. The plant will then live off its stored energy. The dropping temperature also tells plants it is time as trees prepare for winter. The tree's location on earth also makes a difference because it is not the same everywhere. Warmer places have longer summers and the leaves will change colors later in the year if at all.

Source: Google
http://ellerbruch.nmu.edu
"When do leaves change their color?"

Leaves have 3 main pigments. The green in spring and summer is created by chlorophyll which helps plants create energy. When temperatures drop, the production of chlorophyll stops and the amount present in the leaves begins breaking down into simpler compounds. Then other colors, yellow, orange, red and purple, are unmasked. Trees are tuned in to changes in the length of days, light, and temperature. Environmental changes tell trees when to change colors.

Source: Ebsco
USA Today Magazine; Aug95, Vol. 124, Issue 2603, p14, 1/2p.
"Why do leaves change color?"


In autumn or during a dry season, leaves lose their chlorophyll. As the leaves' green color fades, red, yellow, or orange pigments become visible. Trees adjust to the growing seasons.

Source: Britannica Online School Edition
Elementary School. "Leaf."