You may have heard that a wet summer has a big benefit – the rain produces the most brilliant foliage come fall. Summer's not for everyone and I have to admit, it is not my favorite season. But fall seems to rank high on everyone’s favorite season list.
There’s something about those clear pleasant blue sky days with just a hint of tobacco smoke from tobacco barns that makes it special. It seems to be a beautiful time of year that was put there for the 
shear enjoyment of it. Autumn might be the most beloved season of them all. Every year, people watch in awe as the trees begin their magical transformation from green powerhouses to veritable smorgasbords of color.
As the leaves begin to change color, the beauty intensifies and scenes sometimes become indescribable. Let's take a look at what exactly happens when leaves change their colors as the seasons change. First, what "makes" the fall color of a leaf is present from its formation – every leaf already contains pigments. When we see leaves in the height of summer, their green color comes from production of lots of chlorophyll – that green pigment that allows plants to make food from carbon dioxide and water – resulting from all the sunlight they're getting.
As sunlight fades during the fall, chlorophyll production decreases and leaves lose their green. Without that green present, the other colors already in the leaves take center stage. 
Yellow pigment is produced by xanthophyll, orange-red color is caused by carotene and the reddish-purple color comes from the anthocyanin pigment. All those big words probably don’t mean much to you, but what about the question at hand – is there a predictor for a more brilliant fall, or any way to guess when the leaves will be at their best? Summer weather won't do much to influence foliage color.
As I said, chlorophyll is still going strong during summer. It's actually the very late-summer, early-autumn weather from September to October, the time when leaves begin to turn anyway – that affects leaves' appearance. What leaves really need for a good display during this time is clear sun in the day, with nights that are a bit chilly – but not freezing. The warm sun provides the sugars needed for pigment production, and the cold makes sure the sugars don't travel far from the leaf. Further, it's not rain that determines whether leaves are vividly colored.
If you're partial to crimson, you might wonder why nature seems to go overboard with the red some years and forget it entirely during others. The reason involves photosynthesis, pigments and sunlight. To fully understand the chemistry behind the color show, we'll need to look at the proc
ess and those big words we used earlier. As summer nears its end and days get shorter, the increased amount of darkness incites trees to prepare for a sort of hibernation. Leaves won't be able to continue photosynthesizing during winter due to the dry air and lack of sunlight, so the tree does two things. First, it forms a separation layer made of corklike cells at the base of each leaf to seal it off from the tree. Second, it stops producing chlorophyll since it won't need this pigment until the days start to lengthen once again in the spring.
With chlorophyll out of the picture, the yellow and orange pigments get a chance to shine. The red hues, which come from pigments called anthocyanins, are slightly more complicated. Whereas all trees contain chlorophyll, carotene and xanthophyll, not all of them produce anthocyanins. Even the ones that do have anthocyanins only produce it under certain circumstances. Remember that layer of cells at the base of the leaf? Its purpose is to protect the tree during the colder winter and prevent it from drying out. When the separation layer is complete, the leaves fall off in the tree's attempt to conserve energy. But before the leaves fall off and t
he tree closes up shop, it wants to pull in as much sugar and nutrients as possible from its leaves, which is where the anthocyanin comes in. The reason you'll see more vibrant reds during some years is that lots of sunlight and dry weather increase the sugar concentration in tree sap, triggering the tree to release more anthocyanins in a last-ditch effort to gather up energy to get through the winter.
If it's been especially rainy and overcast, you won't see much red foliage. Without bright sunlight, the trees don't need the added protection that the red pigments provide, so they don't bother producing them. So if autumn just isn't the same for you without the occasional splash of red, hopefully the weather will cooperate. If not, you'll just have to make do with the more reliable yellows and oranges. Feel free to comment on this post and be sure to hit the “Like” button at the end.
