Fall leaf colors are due to plant pigments in leaves. The colored pigments are the same that produce colors in flowers and fruits. “Chlorophyll” is the pigment responsible for the green color in leaves, and for producing carbohydrates (sugars) plants need for growth. It does this through the process of “photosynthesis”, producing sugars and oxygen from carbon dioxide and water. Chlorophyll does this through using certain wavelengths of light—primarily blue and red. It is continually being produced and replaced during the growing season.
This information is from The University of Vermont
“Carotenoids” are leaf piments responsible for yellow and orange colors in leaves, particularly in fall. Think of orange, as in carrots. They are present during the season but masked by the green chlorophyll, except in plants that may be stressed or with yellow leaves normally. One type of these carotenoids is “xanthophyll”, coming from the Greek “xantho” for yellow. Carotenoids are responsible for absorbing wavelengths of light that chlorophyll doesn’t—mainly blue-green and green, as well as using excess energy produced in leaves as in high light conditions. In fall, with no chlorophyll around, they may act as a sunscreen. They’ve been around in plants a while, perhaps 3 billion years. Some trees with mainly yellow, or yellow and orange, fall leaves include sugar maples, hickories, beeches, birches, and tulip poplars.
Why sugars are trapped in fall leaves, and why chlorophyll disappears in them, is due to something called the “abscission layer”. This is a separation layer of cork-like cells that develops between branches and leaf stems in response to shorter days (in reality it’s the longer nights) and cooler temperatures. seals off the flow of nutrients between leaf and stems, and eventually roots, which causes the chlorophyll to not be replaced. So it disappears during early to mid fall, leaving the yellow and orange pigments to be seen, and red pigments to be produced.
With time, even these colored pigments break down, leaving brown ones called “tannins”. What colors are produced by what plants, and in what amounts, and when in relation to other plants, is due to the programmed genetics of a particular plant.
Similar environmental cues as those causing red color in leaves also may cause fall colors to come sooner, or later, or to last longer some years than others. Drought during spring and early summer may signal the plant to form the sealing barriers to leaves earlier, shutting down and turning color sooner than usual.
So while moisture is good earlier in the season, too much later in the season means more clouds, less sun, and more muted colors. Too much rain in fall, and strong winds, may cause many leaves to fall prematurely.
Cooler temperatures in late summer (as in August 2014), and plenty of sunshine, often leads to brighter colors sooner. This is particularly true if the sealing layer on leaf stems has started forming. Cool is good, but too cold (as freezing or below) can be bad, killing leaves early. So ideal for fall color would be a moist growing season early, dry late summer and early fall, with sunny warm days and cool nights during the latter.
So for a better color season you need good rain fall in the early season and dryer conditions later in the season with sunny warm days and cool nights and that will lead to a good color season. This season has been warm and wet until this week and now looks to be wet and cool for a while.
Now looking further ahead
It looks like this year will have one of the latest dates for the first day of 40 or below. So, I got to looking and in Grand Rapids recorded history this year will be at least the 2nd latest that the first 40 reading will be recorded in the fall season. On average the first low of 40 or lower is on September 21st the earliest was August 16, 1979 and the latest was October 24, 1914. Other late dates were October 12th 1931. October 11th 1905 and October 9, 2016. Now for anyone who likes to use analog years the news is good/bad. If you are a snow lover the news is not good. But if you like less snow and a milder winter the news is good. The average snow fall at Grand Rapids is around 75” but in the years coming in mid to late October the total is much less than average. With the first 40 or below day coming on October 24th in 1914 the winter of 1914/15 Grand Rapids recorded 51.8” of snow. The winter was also milder than average. Now for the winter of 1931/32 that winter was the warmest on record (so far) here in Grand Rapids and only 41.1” of snow fell that winter. The 3rd latest first 40 day fall of 1905/06 well that winter seen the least amount of snow recorded for a winter season here at Grand Rapids with just 20.0” of reported snow fall. That winter was also warmer than average. Then for the winter of 2016/17 once again the winter seen less snow then average with 60.1” of snow all and the winter was warmer than average
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