by Ashley Andrews, Horticulture Communications Assistant
The autumnal equinox, which marks the transition between summer and fall, has passed. So, it makes sense to see tree leaves turning glorious fall colors. A lesser-known secret about trees is that a lot of their leaves’ autumnal hues have been there all year long. We just could not see them before because chlorophyll was hiding them.
It all starts in spring and summer when the trees put on leaves for the year. The leaves have an important job to do, make food for all of the parts of the tree. Leaves make food using a process called photosynthesis, which turns energy from sunlight and carbon dioxide from the air into carbohydrates for the tree.
A key part of producing those sugars and starches is chlorophyll. Chlorophyll is a chemical that absorbs energy from sunlight. It is with this energy that plants make food. Chlorophyll also has a naturally green pigment, giving plants their green color.
But, this chemical is only one of the pigments responsible for the colors of tree leaves. Along with this green pigment are yellow, orange and brown ones called carotenes and xanthophyll. These pigments are not exclusive to trees. You can find them in carrots too; they are why carrots look orange. They are also in bananas, corn and daffodils. Until fall, though, it is hard to see these pigments in trees.
In fall, tree leaves slow down the food-making process of photosynthesis, getting ready for winter dormancy. Shorter day lengths and cooler temperatures are the signals which tell the trees to slow down. The chlorophyll breaks down and so its green color disappears from the leaves, giving way to the yellows and oranges that have been there all along.
At the same time, other chemical changes in the tree may occur, allowing red and purple tones created by anthocyanin pigments to appear. Anthocyanin is not just for leaves either; it gives other things their color too, like blueberries, plums and strawberries.
Leftover chlorophyll mixes with these fabulous pigments of yellows, oranges, reds and purples. The different mixes create breathtaking fall color changes in trees. Some of these color changes and their timing are due to the tree’s species. While some facets of fall color is predetermined by a trees’ genetics, not everything is set in stone.
How bright the fall colors are and how long we get to experience them varies based on what happened this growing season. We and Mother Nature both influence the fall colors of our landscapes as we both affect the temperature, light and soil moisture our trees experience.
Warm sunny days with cool but not freezing nights bring out brighter colors in our trees. These weather conditions mean bright light and extra plant sugars in the leaves, which leads to anthocyanin production. It is through this pigment that our trees’ leaves shine with palettes of crimsons and purples.
However, early frosts can mute the grand fall display and dry soils can too.
To give your trees the best chance of producing brighter color longer when the temperatures and light provided by Mother Nature are just right, be sure to keep the soil around your trees (and shrubs too) moist throughout the summer and into fall.
While the trees’ leaves seem to change color right before our eyes, other changes are happening in the tree that we cannot see. Where the stem of the leaf connects with the tree, the tree is producing a layer of cells that will separate the leaf from the tree. The tree will seal off that cut, and the leaf will fall under its own weight or by the efforts of a fall wind, leaving behind a scar.
While some facets of fall color are predetermined, no two autumns are alike. So, take the time to enjoy each one. Bring loved ones and all of the fixings for apple cider or hot chocolate on a crisp autumn day tree tour. Tree touring, also known as tree peeping, creates vibrant memories with family and friends that will not fade away with the passing of the seasons like fades the green color of tree leaves.
Fall leaf art for all ages
Some parts of the fall color we enjoy each year are due to things that do not change, like tree genetics. Other parts, like the weather and how we water our trees change a lot about the mixes of pigments in tree leaves and so the fall color we see. This crazy interaction of relatively stable and widely changing variables means that every fall we experience is a unique combination. We can celebrate each individual autumn with homemade art.
Enjoying the fall beauty of our own backyard, town or even country is an experience for people of all ages to savor. As you explore, bring home leaves that speak to you. Look for colors, shapes, textures and anything else about a tree and its leaves that stands out to you.
Bring your finds inside. There, with the red glow of crisp autumn temperatures still on your rosy cheeks, you and your family can create art with your tree trinkets. Two of my favorite leaf crafts involve finger paints.
The first project, good for children and adults of all ages, is tree prints. You can create beautiful tree prints for fall by painting large leaves with different colors. Before the paint dries, press the leaf straight down into clean paper. Make sure each part of the leaf touches the page. Then, lift the leaf straight back up. What you reveal will resemble a full-grown tree. The leaf veins will look like branches.
A craft idea for older children is to create a drawing and accent it with leaves used like stamps. Make a striking impression by embellishing a self-portrait with stamped cascades of painted leaves for hair.
Search online for even more ideas. There are endless ways to experience the art of fall leaves with family and friends.
Ashley Andrews is the horticulture communications assistant with University of Nevada Cooperative Extension. To learn more about trees, attend our class on pruning fruit trees to increase production Oct. 10. Horticulture questions? Contact a Master Gardener at firstname.lastname@example.org or 775-336-0265. Or, visit www.growyourownnevada.com.