LOUISVILLE, Ky. — Leaves changing color and falling off the trees is a clear reminder that winter is on the way. Everyone knows that when the weather gets colder, the leaves will slowly change from green to a stunning combination of orange, red, and brown. Then those leaves will fall.
Not all trees play by those rules, though. Take the Christmas tree in your living room, for instance. If you have a real tree, it will stay green for as long as you decide to keep it in your house. So, how do evergreens keep their verdant hue? (BTW: Artificial trees will also stay green, but we don’t exactly need science to explain that one.)
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Trees with broad leaves that change colors are called deciduous trees. In the winter when there is less sunlight, they produce less chlorophyll. To survive the cold temperatures, they withhold nutrients and water from their leaves and keep those nutrients in their trunks for the next growing season. The lack of chlorophyll in the leaves is what causes them to change colors and fall.
Evergreens are different; they have thin waxy needles instead of leaves. Since the needles are thinner, they are better at holding onto nutrients. There are also more branches on evergreen trees, so they can take in more sunlight. This allows the trees to survive better in colder climates.
The needles on evergreen trees aren’t immortal, though; they do turn brown and fall off. Deciduous trees lose their leaves all at once. Evergreens will lose their “leaves” (aka needles) a little bit at a time throughout the year. That’s why these trees at least appear to stay green through the entire holiday season.
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