Why Do Tree Leaves Change Color In Fall?

Is there anything more magnificent than the colorful leaves of autumn here in Dayton? From bright shades of gold to deep hues of maroon to fiery oranges and reds, the trees seem to shout for attention this time of year. Dayton has its fair share of brilliantly-colored trees in fall – here are our five favorites.

While the colorful display is a great reminder to spend more time outdoors before the weather turns cool (and to complete certain fall maintenance tasks), you may find yourself wondering what causes such an extreme change.

Several factors can play a part, such as shorter days (and thus longer nights), spring and summer weather conditions, and how sunny the fall days are.

Shorter Days (and Longer Nights) Bring Out the Yellows

Chlorophyll is a pigment in leaves that gives them the green color we see during the spring and summer months. It’s also a critical component of the process called photosynthesis, in which energy is absorbed from sunlight and used to turn carbon dioxide and water into “food” for the tree.

Tree leaves also contain yellow-orange pigments, called carotenes and xanthophyll, but they’re typically masked by the intense green of chlorophyll.

As sunlight is such an important part of photosynthesis, the lack of sunlight during the longer fall nights signals the production of chlorophyll to slow down and eventually stop. Without the chlorophyll to block it, the colors of carotene and xanthophyll can shine through, revealing the yellow or gold colors in trees like sycamores, poplars, and beech trees.

Sunny Fall Days Enhance the Reds

If the fall days are bright and sunny, red and purple shades on the leaves of trees such as maples, dogwood and sumac will start to appear. This is caused when anthocyanins are produced from the combination of chlorophyll, the excess sugars, and the bright sunlight.

Nighttime temperatures play a factor as well – if it’s too warm at night to signal a change, the reds and purples will stay muted. If the nights are cool and crisp, the colors will be more vibrant.

Spring and Summer Weather Affect Timing & Brightness

A colorful autumn is very much dependent on the seasons before it. If the trees went through a period of severe drought, the leaves will change much earlier and the color will last for a shorter amount of time. If, however, there was only a moderate drought, the leaf change will happen later in the season.

If the spring and summer were unusually hot and caused heat stress, the leaves can turn brown early and drop.

If late summer and early fall are especially warm, the changing of the foliage can be delayed. Leaves rely on the cooler temperatures as a signal that fall has arrived.

Formula For Best Fall Color

While you can’t scientifically predict how beautiful and vibrant fall foliage will be, there are certain factors that increase the chances of better colors.

If trees received plenty of rain during the spring and summer months, and if the fall is dry and sunny with warm days and cool (but not yet frost-covered) nights, the leaves’ colors should be amplified and longer-lasting.

It’s Not Fall Without Falling Leaves

The longer nights during the fall season stimulate the growth of cells where the leaf meets the stem – called the abscission layer. The abscission layer blocks the flow of nutrients from roots into the leaves and eventually severs the tissue that supports the leaves. When rain or wind hits the leaves, they drop to the ground.

However, not all deciduous trees drop all of their leaves – some species tend to hang onto some until spring. Find out which trees have leaves that hold on through winter.

Not sure what to do with all of those fallen leaves? Why not turn them into leaf mulch, compost or leaf mold?!

It’s a great time of year to collect different leaves from the ground and compare their colors, shape, and characteristics. Walk around your neighborhood or a local park and see how many different types of leaves you can find and/or recognize! It’s a great activity for families or friends to enjoy together.

Check out the Ohio.org website for the annual Fall Color Report to see when leaves in the Dayton area are at peak color, plus fun fall festivals and events around the state.