Jack Frost usually gets credit for the beautiful colors, but, in reality, fall color is controlled by
both the plant's genetic factors and the environment. Carotene and xanthophyll are
yellow pigments produced in foliage all year; along with chlorophyll, the green pigment. In
autumn when short days and cool temperatures slow down the production of chlorophyll, the
remaining chlorophyll breaks down and disappears. Then the yellow pigments that have been
masked by chlorophyll show up. These pigments give the ginkgo its clear yellow color. Redbud,
larch, hickory, birch and witch hazel turn hues of yellow and gold.

Some plants produce anthocyanins (red and purple pigments) that may mask the yellow
pigments. Some maples, dogwood, black tupelo, oaks and winged euonymous seem to be on
fire with red and purple.

Anthocyanin production increases with increased sugars in the leaves. A fall season with sunny
days and cool nights increases sugar content of the leaves and intensifies fall reds. This also
explains the two-tone effect on green ash which exhibits yellow on leaves inside the tree and
purple on the outside leaves where they are exposed to sunlight. It also explains the amelanchier
which may be red on top branches and yellow on bottom branches.

The tans and browns of oaks are caused by tannins which accumulate as the chlorophyll
disappears.

Fall color starts in September with poison ivy and sumac and ends in November with the
larches and weeping willows. Frost and freezing temperatures will stop the coloration process
and blacken the leaves.