Understanding Fall Color
Many people consider fall to be their favorite time of year. Certainly
trees turning brilliant colors is a highlight of the season. While
often associated with frost, how this color change actually occurs
is often misunderstood.
During the season, leaves on trees are green because of the chlorophyll
inside them. Other color pigments are actually present, but are
hidden by the abundant chlorophyll. As the season winds down and
days get shorter, chlorophyll production in leaves slows down as
trees and shrubs prepare for dormancy.
Once chlorophyll breaks down in the leaf, other color pigments
in the leaf become visible. For example, carotene and xanthophyll
pigments give leaves orange and yellow colors. Red color is due
to production of anthocyanins, which is favored by warm, sunny days
and cool nights in fall. Eventually the leaves will dry up and drop
from trees as a wall-like layer is formed where the leaf stalk (petiole)
joins the twig.
Sunny days, and cool nights generally means good color. Frost can
actually be detrimental to the process by causing early drop with
poor color. Some trees under stress have been turning color since
August, because they have slowed in the production of chlorophyll.
Pines and other evergreens may also show color change in fall,
as needles do not stay on the evergreens forever. All the inner,
older needles may turn brilliant yellow or brown at once, and then
drop. Green growth will remain on the ends of branches. Keep in
mind the older needles should be affected only, and there is usually
an abrupt break between the yellow or brown needles and the newer,
green growth as you advance outward on the branch. This is a normal
function of the plant.
October - November 2001: Preparing
Plants for Winter | Heating with Wood Needs
Care and Consideration | Amaryllis for
Winter Beauty | Understanding Fall Color