Autumn Colours

The actual composition in the leaves varies from plant to plant and makes them all behave slightly differently.  Some trees turn yellow rather than red.  The natural loss of chlorophyll in the cold autumn unmasks the yellow carotinoids (yes, the main pigment in carrots) that were there all along.  The trees that turn yellow will reliably do so every autumn as the colour is there and does not have to be made, unlike the red colouration - read on!

As a tree prepares to shed its leaves in autumn, a layer of cells form across the base of the leaf stalk restricting the movement of sugars back into the body of the tree.  Concentrated in the leaf, sugars react with proteins in the cell sap to produce anthocyanin, a purply red pigment that causes apples to turn red and black grapes purple.  Crucially, the production of anthocyanin is boosted by sunlight, drought and temperatures staying above freezing. The perfect conditions for good autumn colour are cold, but not freezing, nights and bright sunny days.  In dry weather the leaf sugars become concentrated and produce more anthocyanin.  Photosynthesis will still take place on sunny days using up the remaining chlorophyll (which is also destroyed by the cold), making the sugars more concentrated leading to more production of anthocyanin.  So the weather conditions makes quite a difference to the autumn colours .... cloudy wet autumns certainly lead to drabber autumn leaves.

All trees do things differently which creates the rich tapestry of colours at this spectacular time of the year.