The northeast certainly drew the winning card, when it comes to fall color. We’re so used to a dazzling display, we too often take it for granted. How do leaves put on such a show? I’d love to slide into winter with as much color as they manage to muster. For now, I’ll just revel in how easily they make the transition. That’s the topic of this week’s podcast. There’s a link below, or you can access it on iTunes and Stitcher. If you’re the type who prefers to read, scroll down below the photo and dig in.
We are definitely in the final countdown for the end of gardening season. No frost yet, but nothing is really growing any longer. The plants are all hunkering down for winter. Podcast will be twice a month in winter, since there’s a lot less going on.
Thankfully we are lucky to have a colorful fall season, here in the Hudson Valley. We’re not quite at peak fall color, but it won’t be long. It’s always such an amazing sight and it’s gone before you’re fully aware it’s happening. Leaves are fascinating structures. Do you realize they are organs of the plant?
What Makes Leaves Green?
During the growing season, the main job of leaves is to feed the plant. They do this through photosynthesis. In order to photosynthesize, the leaves need chlorophyll, which is a green pigment that gives the leaves their green color. Chlorophyll, fueled by sunlight, transforms carbon dioxide and water into the sugars and starches the plant needs. It also gives off oxygen, as a by-product. A nice little bonus.
Chlorophyll is just one of 4 pigments in leaves and most are there, even when all we see is green.
The Color Pigments in Leaves
Green – Chlorophyll is produced by leaves throughout the growing season, provided they get enough light. As the days shorten and temperatures drop, the plant’s metabolism changes (as described below) and other pigments come into view.
Yellow/Orange – The golds and rusts in leaves are from carotenoids, just like in carrots. Carotenoids are present in leaves throughout the growing season, but they are masked by chlorophyll.
Brown – The brown of fall leaves is from the tannins in the leaves. As with carotenoids, tannins are there throughout spring and summer, but hidden behind the green of chlorophyll
Red/Purple – Reds and purples are caused by anthocyanins, like red grapes and wine. Some plants have it all year, others produce it in the fall and some plants lack it totally.
So,What Causes Leaves to Change Color in Fall?
Short days and cooler temperatures trigger leaf senescence, which is a metabolic change that eases plants into dormancy. During the growing season, the leaves go about their job of photosynthesizing and making food for the plant. As fall sets in, the starches and proteins in the plant break down into sugars and amino acids, which are stored in the branches and roots during winter. When photosynthesis stops, it’s this change from making food to storing food that causes the leaf colors to change.
Not all trees are on the same schedule, so colors change in succession throughout fall. Senescence also triggers the formation of a blockage called an abscission layer, at the point where the leaf petioles attach to the twigs. This stops the sugars from leaving the leaves, allowing them to be used to manufacture anthocyanins. (If it is a plant that produces anthocyanins. As mentioned, they don’t all do that.) The resulting colors are a mix of the remaining chlorophyll and whatever other pigments are present. The more sunlight, the more intense the color.
This continues until the leaves drop or freeze. Too much heat, cold, rain, or wind hinder fall color. The best show occurs when we have warm, sunny days and cool nights. Some years are better than others, but it is always too brief, so enjoy it while you can. We should be hitting peak within the next couple of weeks. Be sure to find some time to look up, when you’re outdoors. It’s a great time to take a walk and put down the phone. Maybe I’ll see you out there.