GreenGrass Blog

Lawn Care Info - Why Do Leaves Turn Colors in the Fall?

Posted by Kathy Wilder on Wed, Nov 23, 2011 @ 04:50 PM

beautiful autumn tree

Autumn leaves are as big a part of Thanksgiving as a turkey is!  Sometimes I think we all take the beautiful colors for granted, because we’ve seen them since we were kids, and that’s just the way they are.  And they're a big part of lawn care, 'cuz you have to rake them up.  But why do they turn colors, instead of just dying and falling off the trees?


Leaves are amazing little workers for their trees.  The trees gather up ingredients – water from the soil, carbon dioxide from the air – and then the green cholorophyll in the leaves uses sunlight and photosynthesis to turn them into byproducts of oxygen and glucose, which is food for the tree.


Photosynthesis actually means “putting together with light.”  But as the days get shorter and shorter, as they do in the fall, the trees magically know to produce less and less chlorophyll – such is nature! (the magically knowing thing.)


But here’s the cool part.  The chlorophyll is green.  It’s a pigment that the leaves make.  The leaves also make carotenoid pigment, which is orange, yellow, or brown.  I know you’ve heard that word before, as in “eat your carotenoids” – yellow and orange veggies like carrots and corn, etc.  Another pigment that leaves manufacture is anthocyanin.  I know, it sounds like one of your printer cartridges, but it’s red, and it colors cranberries, apples and other red stuff.


The most important of these pigments is chlorophyll, because it works the photosynthesis magic, making food for the plant.  But carotenoid is always there, too.  You just can’t see it, because the green is covering it up.  As the tree produces less chlorophyll, the carotenoid shows up – voila!  Yellow and orange leaves! 


The red stuff – anthocyanin – is NOT always there.  Most of it is manufactured due to certain weather conditions, and not all trees can make anthocyanin.


So if you notice that fall colors are not always as spectacular as usual, it’s due to the lack of red.  The oranges and yellows are always there. 


Sunny fall weather will produce beautiful reds.  Early freezes and cloudy, rainy weather will prevent them.  A drought may delay them (as well as the oranges and yellows.)


Warm, sunny days will make the leaves produce a lot of sugar, but cool nights may prevent the sugar sap from flowing back down to the tree.  Anthocyanins are produced to help the tree get the nutrients out of the leaves before they fall off.


So now you know!  (Unless you’re a smarty-pants and already knew…) Happy Thanksgiving!


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Topics: autumn leaves