Autumn Colours

by Panny Laing

Have you ever wondered why leaves become such wonderful colours in the autumn?  Well, as so often, there is a bit of science to the process.

Starting with the green colour in the leaves. Chlorophyll is the green photosynthetic pigment found in plants, algae and some bacteria; it captures the energy in sunlight to convert carbon dioxide and water into sugars which are then transported around the plant and stored in the leaves.  Plants need sunlight and warmth to produce chlorophyll (think of the colour of grass when it has been covered for a while), which is also destroyed by bright sunlight.  In summer it is continuously created keeping the leaves green.

Logie House Garden in Autumn

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!

 

Darmera peltata

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.

 

Acer capillipes

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

Logie House Garden is open to the public every day (10am - 5pm),

as is Logie Steading Farm & Garden Shop (10am to 5pm, 4pm in winter)

where many of the plants for sale are propagated here in the garden.