Weather conditions impact fall leaf colors

This is an incredible and beautiful fall. Everyone is enjoying all the color and beauty of this season. Are there special ingredients that produced such beauty this year?

— Ginnie


Weather has a big impact on the annual fall foliage show, according to the United States National Arboretum.

A growing season with ample moisture followed by a dry, cool, sunny autumn with warm days and cool, frostless nights provides the best weather conditions for development of the brightest fall colors, according to the arboretum.

During the growing season, chlorophyll keeps leaves green, masking the yellow pigments called xanthophylls and orange pigments known as carotenoids that are also present in the leaves. In the fall, the production of chlorophyll slows and then stops, revealing yellow and orange pigments, according to the arboretum.

Red and purple pigments called anthocyanins are manufactured in the fall from sugars trapped in the leaves. In most plants, those red and purple pigments aren't present during the growing season, according to the arboretum.

Cool nighttime temperatures and abundant sunlight promote the formation of more anthocyanins. Freezing conditions destroy the machinery responsible for manufacturing anthocyanins, so early frost means an early end to colorful foliage.

Other weather factors that can negatively impact fall leaf colors include drought during the spring growing season and heavy wind and rain knocking leaves off trees too soon in the fall.

Trees in the Rogue Valley received plentiful rain this spring followed by a dry summer and only occasional rain and wind so far this fall.

— Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to We’re sorry, but the volume of questions received prevents us from answering all of them.

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