Pretty much all the questions you raised have an impact on leaves changing in the fall. I'm not as much as an expert as many of those on this site, but I'll share what I know. Length of daylight, or the decrease of it in the fall is the main factor that changes leaves. In Chicago where I live no deciduous tree can stay leafed up all winter even if there is a record warm winter. Although this is may not always be the case in the far deep South or the Florida panhandle.

Temperatures have a huge impact on leaves changing. This fall in Chicago has been an average fall temp wise and the leaves are now at their peak, which is the normal time of year. Fall of 2007 was one of the warmest falls on record and the leaves didn't change until the beginning of Nov. Fall of 2006 was a very cold fall, with an early frost in early Oct. This lead to the leaves changing early and virtually no trees had leaves on them on Nov 1st.

Frosts speed up the leaves changing. Strong wind or rains can strip the leaves off the trees early. Drought usually takes away from the color quality and most leaves just turn brown and fall off. Adequate moisture with sunny days and cool nights brings out the best color. This has been the case so far in the Chicagoland Area this fall, and the colors have been great so far.

The one thing that I'm not sure of is how the acidity of the soil impacts leaves changing? You always hear that the East Coast has a better leaf show than the Midwest and that the soil being more acidic there is one reason for it. How much does soil acidity effect the color change? I'm also guessing that being closer to the ocean and having less early frosts can be a reason too?

I hope this helps you out

Jeff

{{gwi:466919}}

I can say that at least where I live, the majority of species renowned for their bright fall colors do not thrive here where I live on the plains. The majority of endemic trees around here turn a good yellow at best.

Some of the red maples seem to color up better in acid soil. Alot of trees with better fall color ive noticed grow on slopes where the soil is well drained.

Our fall color here hasn't been as good as usual, we've had an incredibly dry latter half of the season.

Reds are caused by anthocyanin pigments dissolved in the cell sap. These are formed by a chemical reaction of sugars with anthocyanidins. They are enhanced by bright sunlight, low temperatures ABOVE freezing,and dry weather. Acidic cell sap gives brighter reds, more alkaline sap produces purplish tones. Soil pH might factor into cell sap pH.
Yellows are produced by carotenoids (carotenes and xanthophyll pigments). These are in chromoplasts, little chloroplast-like bodies similar to those in which chlorophyll is made. Their color is revealed by death of the chlorophyll, though they were present all along.
Winter leaf retention has nothing to do with winter warmth. It occurs in some species, generally on lower limbs close in to the trunk (marquesence)due to failure of a corky abscission layer to form that allows the shedding of the leaf.

jlaitar,

What exact ash tree is that? Gorgeous!

Here's a picture of 'Fire Dragon' shantung maple growing in caliche soil (high pH) last year. I'm curious to see how it'd do this year. This fall is about as perfect fall as you can get compared to previous years so it may help with the fall color although lack of rainfall and very hot weather all summer may prevent that. Last year was pretty good for Dallas area.
{{gwi:340439}}From Fire Dragon 12-1-2007

I asked why my burning bush doesn't get as red as I have seen. I have it planted as a foundation plant so is shaded from morning sun. I was told they get more color if planted w/ full all day sun.

Many variables come together, but what I hear is that generally sunnier drier weather leads to better color years.

But, the older I get the more I value the surprise or chance factor. If they were all "great" we'd start taking them for granted.

Around here, it seems that every year is better for some varieties than others. Last year the ornamental pears just really popped. Two years ago the red oaks loved the weather we had for fall. Three years ago it was the C Pistachios. Funny.

The suspense on how this one will work out rises by the day. ;)

In Colorado, it's always hit or miss with the color. More and more people are TRYING to get colors other than yellow or green in the fall. This year has been an amazing year for bright yellow, great oranges and bright reds. We actually had normal fall temps (meaning warm days, cool nights, and a later season rain). I'm not sure if this had anything to do with it, and I'm very interested in the exact answer!! I do know that I get better color out of my trees if I stress them late summer/early fall with less water...

Here is an explanation of how and why and what helps the most.

Here is a link that might be useful: A scholarly explanation of why leaves change

Hey pinetree30

I only said that some trees don't shed their leaves every winter in a warm climate because a buddy of mine that I grew up with in Chicago moved down to Tampa, Fl five years ago. He planted a Chinese Elm next to his patio and the first three winters he was down there his tree never had it's leaves change color and drop. However the past two winters he had cold stretches in December and the tree did drop its leaves, only to leaf back up at the end of February.

One thing that seems to be missing from this discussion is that the tree has a heavy influence on microclimates that occur IN and AROUND the tree. The most obvious is sunlight, and the shady side of a tree, but it is also temperature as well, and radiational cooling of the most exposed part. Have you ever noticed that small tends to vary in fall color over the tree, than a large tree. A small tree is more exposed to it's surrounding environment, where a large tree impedes air circulation through it, slows the escape of infrared radiation (it travels a short distance before being absorbed by another leaf) from it's central areas, as well as retain higher relative humidity in the inner areas of it's canopy. This probable has allot to do with why you frequently see trees that are green in the interior of their canopy, but brightly colored on the margins of the canopy. Also would explain why for many trees the tips of branches and top of the trees will often turn first. They are the most exposed to radiational cooling.

JMHO
Arktrees

I may be one of the oldest observers of autumn color changes here--more years of careful observation. First, pine tree has it right about the differences between the yellows and the other colors. And beyond that, not all species of trees react the same to the same weather conditions and other possible factors such as soil. There is so much that can influence color that I canÂt really cover very much without writing more than this forum usually tolerates.

But just for one example, I will focus on the maples and weather factors. To make this as brief as possible I will make a list.

1. A real freeze generally ruins color for the season--something like 28 degrees or so.

2. Cool nights, warm sunny days--60 to 70 degrees--really help a lot.

3. Dry winds generally dull color, and if it is really dry--low humidity and winds, color will not have much real vibrancy, and it will be more brief. If it is really warm, windy, and dry, the color is diminished even more.

4. Unless there is a very, very dry late summer and fall, lack of rain makes no difference. Same with too much rain.

Some of the best color comes in years when people think the conditions are the worst. The best year I ever saw for color in the Washington, D.C. area came after a week long period of cloudy skies and drizzle. This period came right at the time the color usually started. Then the skies cleared, the warm sunny days and cool nights came with high humidity and no winds. Nothing I can write here could begin to describe the color--really mind-blowing, etc. etc. The best I had ever seen! But everyone was moaning the week before about how the color for that year was ruined.

--Spruce