I set out yesterday to photograph one of our cherry trees in its autumn colour. What I got is not at all what I had hoped for.

Here’s what the tree looked like a year ago, almost to the day. That was what I wanted to capture again but from a different angle. And next to it, what it looked like yesterday:

Compared to last year, the tree looks rather unimpressive. Where’s that fabulous fiery red gone? The top of the tree is already starting to look sparse so waiting will not help.

I thought that the colours we see in autumn leaves are always there, but hidden by the strong green of chlorophyll. In autumn they become visible as the chlorophyll is broken down before the leaves fall. But if that was really the case then a tree should look pretty much the same year to year.

I’d noticed already last year that there was more red on the side of the tree that faces the sun, and mostly yellow in the shadier parts. So there’s obviously some dependence on sunlight.

Now I did some reading and found out that the schoolbook explanation for autumn colours is only half of the truth at best.

The orange and yellow pigments (carotenoids) are indeed there all year round, as the schoolbooks say. But the red pigments (anthocyanins) are only produced in autumn when chlorophyll starts breaking down. And some kinds of autumn weather lead to more anthocyanins than other kinds:

The range and intensity of autumn colors is greatly influenced by the weather. Low temperatures destroy chlorophyll, and if they stay above freezing, promote the formation of anthocyanins. Bright sunshine also destroys chlorophyll and enhances anthocyanin production. Dry weather, by increasing sugar concentration in sap, also increases the amount of anthocyanin. So the brightest autumn colors are produced when dry, sunny days are followed by cool, dry nights.

(scifun.org)

Additionally I learned that anthocyanins are also the pigments in cherries, but also eggplant skin, blueberries, raspberries, blackcurrants, apples and all sorts of other red and purple fruit and vegetables. And the dependence on sunlight explains why often only one side of the apple is red while the other is greener.