Kinghorn Gardens

Fall Color 101

October 13th, 2009

As Nebraskans we have to deal with a lot of different weather conditions.  None are more dreaded than the onset of a long, gray winter.  However, we are rewarded for all which we must endure.  Our reward is in the form of fall color.  Each year we are treated with the wonder of leaves changing from green to fiery hues of orange, red, yellow, purple and everything in between.

But how and why do leaves change color?

There are three factors which have an influence on fall color:

1. Leaf pigments
2. Photoperiod
3. Weather

It makes sense for a pigment to have an influence on fall color, but just what are they?

• The first, chlorophyll, I am sure we are all familiar with.  It is what make leaves green, and allows plants to turn sunlight into food (in the form of sugars).
• The second, carotenoids, gives leaves the colors of yellow, orange and brown.  They are always present in the leaf, but do not make their debut until fall.
• The last, anthocyanin, give leaves red and purple coloring.  Anthocyanins are developed in late summer and their formation depends on certain proteins in sap and sugars.  This process does not occur until the levels of sugar are high.  The process also requires light.

Just what is Photoperiod?

Photoperiod is the duration of an organisms exposure to light.  For our use, it is the length of day.  As summer ends and fall commences, the hours of daylight decrease.  Since plants turn sunlight into food, this is important because they now have a shortened duration of time in which to synthesize chlorophyll.  Plants take this reduced period of light as a warning, and begin their process of becoming dormant.  During this time of shortened days and lengthened nights, chlorophyll production slows, eventually stops and then is destroyed.  Water and other nutrients are sucked out of the leaves and back into the plants stems, leaving the anthocyanins and carotenoids to be exposed.

The influence of weather

The intensity of fall colors is affected by temperature and moisture levels.  A late spring, or summer drought can delay the timing of fall color by a few days or weeks, while a warm period during the fall can also lessen the intensity of colors.  The most spectacular displays seem to occur after a series of bright, sunny days followed by crisp, cool - but not freezing nights.