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Why leaves change color in fall

I had written an article on leaves during a series on plants. I wrote about the green called chlorophyll.

Green is the color of life, nature, health and prosperity. It is hope in the spring; the renewal after winter.

So, now that it is autumn, where do all the colors come from?

Pigments in the leaves make the colors we see. In the spring and summer, we see green — the longer daylight, more rain and warmer temperatures mean plants are busy with food production.

The chloroplasts (containing chlorophyll) in the presence of sunlight and water utilize the process of photosynthesis to make sugar, the food of plants. This food allows the plants to grow, blossom, and bear fruit and seeds.

Carotenoids are pigments that produce the yellows and oranges in leaves, but throughout the summer months these are masked by chlorophyll.

As the days get shorter and the nights get longer, and as the temperatures drop at night, an abscission layer forms at the base of the petiole (the stem that holds the leaf to the branch).

This triggers changes in the leaf. First, the sugars manufactured in the leaf build up, instead of being transported down through the veins to be stored in the roots.

Chlorophyll begins to break down to reveal the carotenoids. This causes the yellows and oranges we see.

At this time, anthocyanins are manufactured, making the reds, purples and crimsons that are so beautiful.

Trees have inherited color traits. Sugar and red maples have red colors.

Aspens and birches have yellow. Some are orange, while others are purple.

As well, trees inherit timing factors as to when they change. Thus, we can estimate when we will have the peak color! Conifers, as well as hardwoods, produce yellow and brown needles on 2-year-old or older needles.

Pines and spruces shed these needles, causing some people to think their tree may be dying.

They shut down food production, but do not go totally dormant.

Larches and bald cypresses turn red brown before they lose their needles or fronds. They go dormant for the winter.

So, the shorter days / longer nights, cooler nighttime temperatures, humidity, amount of sugar stored in the leaf and rainfall all contribute to the amazing show that we call autumn!

Hughes is an Ohio State University Extension Master Gardener Volunteer in Mahoning County.

Starting at $3.23/week.

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