A foggy day in Shropshire, and I found myself humming the old George and Ira Gershwin classic about London Town as I went about my business, the colours of the trees and shrubs in the garden filling me with anything but alarm as they emerged from the gloom when the sun broke through.
It's been a good year for autumn colour. Probably because of the mild, wet weather we've had. If it hadn't been for that one night when the temperature fell below freezing, followed by a day of strong winds, it would have been even better, but the vine lost most of its leaves to that, and other things were touched by it enough for them not to be at their best anymore.
Not that the weather is the main reason we have autumn colours to enjoy, only how long it lasts some years. The main cause of autumn colour happening is the increasing length of the night.
Colours in plants are the result of the pigments present. Chlorophyll, which is present throughout the growing season, gives us the basic green. Carotenoids, also there all year, produce yellows, oranges and browns. Anthocyanins, which increase their presence in autumn, give the colour to such things as red apples, cherries, strawberries and plums.
As night length increases in the autumn chlorophyll production first slows down, then stops, and the chlorophyll is destroyed, leaving the other two pigments free to display their own colours.
When in early autumn, in response to shortening days and the declining intensity of the sunlight, the veins in the leaves gradually close off, a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaves and promote production of more anthocyanins. Once this process is complete and the connecting tissues sealed off, the leaf is ready to fall.
In the garden, look out for a plant which doesn't change colour in autumn, because it is an evergreen. Fatsia japonica, the Japanese aralia, has large, palmate, glossy dark green leaves all year round, but bears dense clusters of globular milky white flowers in November, which are followed by round black fruits. It is frost hardy, but needs shelter from strong winds in cold areas. The leaves of the variety 'Variegata' have marginal variegations.
