FARGO — Have you heard the latest? Rumor has it that early fall color appearing on some trees and shrubs means the upcoming winter will be brutal, with record-setting bitter cold, and snow depths seldom seen in modern history.

Can this be true? Does the wise old oak tree know something we don’t?

There’s an old saying that suggests if you haven’t heard a rumor by 10 a.m., you’re supposed to start one. That’s perhaps how the bone-chilling winter forecast started.

Weather folklore is fun and fascinating, but it can be problematic because it often doesn’t pan out. Although it makes for interesting small talk, fall color doesn’t predict the future. Instead, the arrival of autumn foliage color is a response to conditions that are currently happening, or have already happened, not future events.

As fall approaches, plants respond to the current shorter days and weakening sunlight and begin dismantling the summer photosynthesis machinery. Chlorophyll breaks down, green pigments fade and other leaf colors are unmasked, revealing leaf pigments such as yellow carotenoids. Trees and shrubs displaying yellow fall color have simply had their pre-existing yellow pigment unmasked by the breakdown of green chlorophyll.

Leaves change color as trees respond to shorter days and weakening sun intensity. David Samson / The Forum
Leaves change color as trees respond to shorter days and weakening sun intensity. David Samson / The Forum

Because these pigments are always present in the leaves, yellow and gold fall colors remain fairly consistent each year because they are triggered by the calendar’s short days. Besides yellow fall colors, some trees and shrubs turn red, orange and scarlet, which depends on the types of plants and the fall weather.

When night temperatures begin consistently dropping below 45 degrees, sugars in plant sap are trapped in leaves where chemical reactions convert sugars into red and purple pigments called anthocyanin. Not all types of trees and shrubs have the necessary building blocks for red and orange pigments, which explains why some types remain yellow. Orange and copper shades are created when newly produced red pigments blend with yellow pigments.

The longest, brightest fall color happens when days are sunny and nights are cool, but frost-free. Sometimes, frost is falsely believed to enhance autumn color, but frost actually shortens the fall display. Too many freezing nights cause leaves to detach from their twigs and fall to the ground. Warm, wet weather often diminishes fall color, which is often intensified in cool, dry autumns.

Why do some trees and shrubs turn color early? The University of Michigan says certain factors can cause leaves to change color early or out of sync with their neighbors, such as trees on the edge of low-lying areas where cooler air collects at night, causing them to display colors sooner. Trees that are stressed or in decline may also display fall colors earlier than their healthy neighbors do.

Early sightings of fall color are often single trees sticking out visually in mostly green stands of trees. The lone tree frequently has been stressed in some way, and the stress might even go back a year or two, such as being too wet or too dry.

In areas where new homes have been built, soil compaction can cause stress that might not show up immediately. Trees and shrubs that have been transplanted within the last few years frequently develop autumn color faster than well-established trees of the same type.

Although it’s fun talk around the coffee shop, there’s no historical correlation between early autumn color and severe winters when examined after the fact. Likewise, a heavy seed set on trees hasn’t correlated historically with the winter that follows, which is another folklore weather forecaster that unfortunately hasn’t proven accurate either.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at kinzlerd@casscountynd.gov or call 701-241-5707.