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September 30, 2013

Many factors influence fall color

The northeastern United States is one of the few locations in the world that develops intense fall color (along with northern areas of China, Korea and Japan), and in the Champlain Valley we are just hitting our stride. 

Many factors influence fall color. The yellow and orange pigments are always present in the leaves; they are just masked by the green chlorophyll until fall. As the leaves get ready to drop, the green fades away, revealing the yellows and oranges.

The red color that also contributes to the intensity of the purples and oranges is a result of accumulated sugars in the leaves. The red pigment it produces is called anthocyanin. The amount of red in the leaves is directly related to the weather that occurs while the leaves are turning. The weather during the growing season has little, if any, effect on fall color.

The best conditions for producing the red color are just what we’ve been having a lot of lately: cool nights and sunny days. Nina Bassuk from the Urban Horticulture Institute at Cornell University explains it this way: “It is this combination of sunny days and cool night temperatures during the time when leaves change color that determines whether it will be a good or great year for fall color. Rainy, overcast, warm weather during this time will produce a display rich in yellows but poor in reds.”

TREES AND COLOR

Each species of tree turns its own distinct color. For example, birches and Norway maples turn yellow, while sugar maples turn orange to orange-red, and our native red maples turn scarlet. Our native white ash trees turn beautiful shades of purple, while the green ash, which is the type sold in nurseries, turns yellow.

When you shop for trees to add to your landscape, consider their fall color. Many cultivars have been selected particularly for this. The serviceberry “autumn sunset” has pumpkin-orange fall color, while “cumulus” has yellow to orange-scarlet color. Within the red maples (not the red-leaved Norway maples such as “crimson king”) you can find many good choices.  “Autumn flame” has early, long-lasting red leaves in fall, while “northwood” has more of an orange-red color.

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