The Unfolding Colors of Fall

The autumnal equinox arrived September 22nd, signaling a transition in day-length patterns and ushering in the fall season. On the equinox, the sun shines directly on the equator and the length of day and night
is nearly equal. The word equinox means “equal night”. As the weeks march on, the earth tilts on its axis and the Northern Hemisphere is farther from the sun, decreasing the amount of time the sun is over the horizon, changing our weather patterns and creating distinct seasons.

Norway maple and dogwood on the Garrison Grounds

The fall season at the King’s Garden is marked by late blooming perennials, visits by monarch butterflies, and our Heritage Harvest
and Horse Festival. The festival takes place on September 29th and features a plant sale, equine demonstrations, a harvest market of locally grown and produced items, horticultural talks, a six-acre corn maze and children’s activities, including a tree scavenger hunt. The majestic trees around the garden grounds are the focus of the activity. This time of year, I am often asked, “What will the colors be like this fall?” referring to the changing leaves.
It is longer nights that are responsible for the chemical changes in deciduous leaves that create a tapestry of color in the autumn landscape. Northern New York and New England are famous for fall color that can be attributed to the density and diversity of tree species found here. There are over 60 varieties of color producing trees that exhibit the glowing reds, yellows, oranges and russets that create colorful vistas in the mountains and valleys.

The massive bur oak near the King's Garden

So where do these colors come from? The green pigment
chlorophyll is abundant in the leaves throughout the summer as it carries on the job of absorbing the energy from sunlight needed for photosynthesis. Photosynthesis uses carbon dioxide, water and sunlight to make sugars necessary for a plant’s survival. Chemical changes take place to prepare a tree for winter, triggered by change in day length and temperature.

A complicated process begins to take place inside the leaf. Chlorophyll production stops, veins that carry sugars out of the leaf gradually close, and a specialized layer forms that severs the leaf from the branch. As the chlorophyll fades, other pigments are revealed. Yellows are fairly constant
from year to year since the compound carotenoid is always present in the leaves of birch, locust, and poplar, to name a few. Red and purple hued leaves are more brilliant when warm sunny days produce sugars which are then trapped in
the leaf when the night cools, causing the formation of red pigments called anthocyanins. Varying amounts of chlorophyll residue and pigments produce the different shades.

The pigment anthocyanin is found in barberry fruits

Each tree species displays a dominant autumn color that is more or less intense based on environmental factors. Degree and duration of
fall color depends on temperature, light, and water supply over the entire growing season. The checklist below offers some clues to determine the
potential brilliance of fall foliage.

COLOR FACTOR CHECKLIST
Positive Factors
Warm spring
Wet spring
Summer not too hot; limits stress
Summer not too dry; limits stress
Warm sunny fall days to produce sugars
Cool fall nights, not freezing
Negative Factors
Severe drought can delay arrival of color
Warm, wet fall lowers intensity of colors
Severe frost browns the leaves, early drop
Cloudy fall days
Early onset of cold weather – the leaves may not drop

Tannins give oak leaves a russet or brown color

Autumn is a time of transition from an actively growing tree
to the dormancy of winter. All parts of a broadleaf tree except the leaves can
endure winter temperatures. A leaf releases from the branch when a corky layer is formed at the base of the leaf stalk, thus sealing the twig from water loss. Sugars stored in the branches, trunk, and roots sustain the tree until it awakens in spring. Buds form in the fall and lie dormant until after the spring equinox when lengthening days and warmer temperatures bring the promise of renewed life to the winter landscape. It seems that because autumn colors are fleeting, it adds to their appeal. We have had conditions from both the “positive” and “negative” checklist, so maybe this year will be just right.

Heidi teRieleKarkoski
Curator of Landscape
This entry was posted in Horticulture, Landscape and tagged , , . Bookmark the permalink.