Posted on | October 11, 2008 | No Comments
There is a sense of defiance to be found in autumn foliage colour – one last exotic explosion and then it’s all over until next year. And, while it lasts, that final magnificent moment can leave unrivalled memories to enrich the empty months that separate us from the confident exuberance of the spring and summer to come.
As we head into mid-October with the autumn equinox fast approaching and the sun much lower in the sky, the leaves turn through countless shades of green, gold and red to deep bronze, purple and brown and should not be missed but enjoyed for their short transient phase as they move from summer to winter.
What autumn lacks in flower colour is more than made up for with the fiery leaf shades that many trees and shrubs produce as the days shorten. All this happens because of cooling outdoor temperatures working on the sugars within the leaves, exposing pigments which, until then, remain hidden.
Leaves contain a variety of chemicals that only absorb some wavelengths of light within the spectrum of white light. Leaves that are green have that colour because of the chlorophyll inside them. This pigment absorbs red light while reflecting yellow and blue light and so appear green. In autumn, deciduous trees, those that lose their leaves in winter, need to absorb some of the nutrients in their leaves before they drop off and decompose, consequently feeding the plants roots.
It would be a waste of resources for the tree to discard leaves full of active chlorophyll, so a process called senescence is set in motion. As many nutrients as possible are re-absorbed and then pigments in the leaf are broken down. As the leaf dies, the chlorophyll is replaced by pigments such as anthocyanin, which is red and beta carotene, which is yellow.
This chemical cocktail of breakdown products in the leaves is responsible for the glorious autumn displays before the leaves fall into drifts of fabulous colours on the ground, creating a wonderland of colour for us to enjoy. My house at the Exotic Garden goes through a glorious transformation itself at this time of year.
It is clothed from foundation to chimney top in scrambling Virginia creeper, Parthenocissus quinquefolia, and every year I am amazed by the speed of the colour transformation, as its leaf colouration changes from dark green into warm hues of ochre, auburn, deep red and burgundy before leaf fall.
A similar self-clinging climber Boston ivy, Parthenocissus tricuspidata, also turns brilliant shades of red, yellow and purple until it appears as though the leaves are made of fire! The dark red-purple foliage of the shrub Cotinus cogeria ‘Royal Red’ complements the smoke-like fuzz of tiny pink-purple flowers in summer, but in autumn the leaves of this handsome deciduous shrub change to a brilliant red, as does C. ‘Grace’, another truly splendid variety with leaves that turn to a vibrant, glowing red. C. ‘Royal Purple’ is another gorgeous form with purple wine-coloured foliage that becomes duller towards autumn when it turns a rich red.
Aesculus neglecta ‘Autumn Fire’ is a superb small tree that’s native to the south-eastern United States. The foliage is a coppery colour when it emerges in spring, turning dark green in the summer. It then explodes into a kaleidoscope of red, orange and yellow during the ever-shortening days. It is not until autumn that the real reason for planting Parrotia persica becomes apparent.
At this time of year, the glossy green leaves begin to change colour and a veritable cornucopia of hues appear. Rich crimsons, brilliant yellows and warm ambers fight for attention but in the end always seem to complement each other to form a spectacular autumn show for our delectation. I cannot conclude without mentioning Liquidambar styraciflua, or Sweetgum, thus named by the Spanish naturalist Hernandez, who was the first European to discover this beautiful tree in the early 16th century.
It was given its botanical name because of its aromatic gum, which Hernandez described as ‘liquid amber’. It wasn’t until 1681 that this fine tree was introduced to Britain by the missionary plant collector John Bannister. It is grown in British gardens solely for the magnificent colours of its autumn foliage, which turn brilliant shades of purple, crimson, orange and yellow, deservedly making it one of the most popular of all ornamental trees.