Everyone likes to make a good impression. When we meet someone, they make an effort to “put their best foot forward” and only after you have been with them a while do you really get to know them. Some plants are the same way. Take the weeping cherry, for example. Most people are introduced to it in the spring, when showy flowers catch your attention. It’s certainly a beautiful tree. All summer you enjoy the shade of nice green leaves. Then fall comes and it shows its true colors – yellow leaves!
Yep, many deciduous trees change color in the fall. Why? Three reasons – chlorophyll, carotene, anthocyanins. They are big fancy names for the chemicals providing the pigments found in leaves. Chlorophyll gives us green, carotene gives us yellow to orange pigments and anthocyanins provide some leaves with red to purple pigments.
Most kids learn that leaves are green because they have chlorophyll in them and the chlorophyll is what converts the sun’s energy to food for the plant. The plant does this all spring and summer. Chlorophyll is constantly breaking down so the plant must continuously make more. Some plants drop their leaves in the fall, so when they get ready for the autumnal shedding, they stop making chlorophyll as the nights get longer and less sunlight is available. As a result, the green pigments eventually disappear and other colors emerge.
If a leaf has carotenes, they are present in the leaf all through the summer. When the chlorophyll fades, a yellow brilliance is finally revealed. Other leaves start producing anthocyanins in the fall because of extra sugar present in the leaf. As a result, we get brilliant reds and in some cases purple. Either way, we get beautiful color.
These changes occur because the amount of light affects chlorophyll production, but weather can impact their intensity. Cool, but not freezing, temperatures combined with bright sunshine and dry conditions help speed the loss of chlorophyll and increase the sugar needed for anthocyanin production. Therefore, sunny days followed by cool, dry nights give us the brightest colors.
We tend to think of trees as producing all this fall color, but don’t forget that shrubs and even some perennials do the same thing. Look for the brilliant red of Virginia sweetspire or the golden hues of the blue starflower. In any case, this is the time of year to walk around the Garden and see what many plants are really like – showing their true colors.