25 October 2013

Autumn Almanac

Autumn is officially here. For the past week or so the trees around the car park at Hill Top have been slowly shedding their leaves onto the tarmac and every few days I've been slowly blowing them onto the grass edges with my trusty leaf blower. I work on a 'little and often' principle with leaves, figuring it's easier to blow a few leaves off regularly than great soggy piles less frequently.

Apparently, before the 16th century the season between summer and winter was known as Harvest but was gradually replaced by Autumn, from the French Autompne (derived from the Latin Autumnus); and Fall from the Middle English expression 'the fall of the leaf'.

During the 17th century, English emigration to the British colonies in North America was at its peak, and the new settlers took the English language with them. While the term fall gradually became obsolete in Britain, it became the more common term in North America. Two nations divided by a common language!

So why do leaves change colour in the Autumn anyway? Well, at the risk of sounding like a dodgy shampoo commercial, here comes the science bit!

Plants convert sunlight, carbon dioxide and water into sugars by a process called photosynthesis. The energy from sunlight is captured by a green pigment in the leaves called chlorophyll which is short lived and needs to be continuously renewed throughout the spring and summer. In the Autumn, when day length and light intensity decrease, the tree stops producing chlorophyll. As the chlorophyll fades, other pigments which are present in leaves all year but are masked by the green chlorophyll become visible. The main one of these is carotene (the same thing that makes carrots orange).


As a tree prepares to shed its leaves a layer of cells form across the base of the leaf stalk which restricts 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. This gives some leaves their fiery red colours.

Chlorophyll, carotene and anthocyanin all at once!

Once the layer of cells (technically known as the abscission zone) has completely blocked off the leaf, a tear line forms and eventually the leaf falls from the tree. A protective layer seals the wound, preventing water evaporating and bugs getting in. Simple really!

I'll leave you this month with two poetic takes on Autumn, the first from Robert Frost-                     

Gathering Leaves

Spades take up leaves
No better than spoons,
And bags full of leaves
Are light as balloons.

I make a great noise
Of rustling all day
Like rabbit and deer
Running away.

But the mountains I raise
Elude my embrace,
Flowing over my arms
And into my face.

I may load and unload
Again and again
Till I fill the whole shed,
And what have I then?

Next to nothing for weight,
And since they grew duller
From contact with earth,
Next to nothing for color.

Next to nothing for use.
But a crop is a crop,
And who's to say where
The harvest shall stop?

And the second from the Kinks  click here

See you next time..

Words and pictures by Pete the Gardener