The Colours of Autumn
PUBLISHED: 19:32 04 October 2007 | UPDATED: 14:52 20 February 2013
What better time of year the October and November to visit a garden in search of plants that are great for seasonal colour? We look at the science behind autumn colour in plants offer advise on which Cornish gardens to visit for a real burst of se...
Plants are, with a few exceptions, the machines which provide the world's energy, using the sun as their main fuel. The energy obtained from coal, oil and gas is the sun's energy stored by plants millions of years ago. Plants are therefore machines, and as such need chemicals to function and, like most machines, produce waste products. Photosynthesis, the process of capturing and storing the sun's energy, occurs when carbon dioxide from the atmosphere is combined with water to make carbohydrates (sugars). A major byproduct is life-giving oxygen. To release the energy, oxygen is required and water and carbon dioxide are released.
If we could get plants to store more energy, or produce machines which carried out photosynthesis on a massive scale, storing more energy than is being used, then the world's problems of increasing carbon-dioxide levels would end. This is, of course, a very simplistic description of a complex process.
The chemical side of photosynthesis is most noticeable in the leaves of deciduous plants. Chlorophyll, the major chemical directly responsible for combining the sun's energy with carbon dioxide and water, tends to be green and masks most other colours within leaves. When leaves begin to die, chlorophyll dies too and the colours underneath are revealed.
In the autumn, green chlorophyll can die before these coloured chemicals. But that is not the whole colour story. Whenever the sun shines and the temperature is high enough, plants will manufacture energy-storing sugars. If the concentration of sugars were to become too great the plant would pickle itself, so it stores the sugars as starches and oils, using them for tissue formation and other substances, many of which are coloured - purples, reds, oranges and yellows. Like all machines, plants produce waste products, many of which are brown. Quantities of these are stored in leaves, to be disposed of during leaf fall.
Think of a painter's palette and the various combinations of these coloured chemicals and you have the colours of autumn leaves. Reds and yellows provide orange, and yellows and purples make brown and, if mixed with too much brown waste, the leaves are just various shades of brown.
Gardeners make use of these processes to get the best autumn leaf colour. The secret is to have healthy plants, making lots of sugars, and then prolonging the period between green chlorophyll loss and leaf fall. A drop in temperature in the autumn reduces the speed at which plants can convert sugars to starches and oils, so instead they convert more sugars to coloured chemicals; plants should therefore be exposed to the sun in the daytime and to the cool air at night.
Get the right weather and timing, and the colour of beech, oak and larch, together with elder, spindle and viburnums, can almost rival the maples of New England in the fall
However, as very cold conditions, especially frosts, induce rapid leaf fall, plants need some protection. An ideal situation is provided for many plants, especially shrubs, by an overhead canopy of light foliage, which reduces the effects of radiation frosts, whilst admitting a certain amount of sunlight. Drying winds and shortage of water at the roots will also cause premature leaf fall.
Some plants are more reliable than others at producing autumn leaf colour and over the years these have been selected by gardeners and nurserymen. The best known are the maples (Acer), but displays from deciduous spindles (Euonymus), deciduous azaleas, Fothergilla, dogwoods (Cornus), Persian ironwood (Parrotia) and deciduous berberis and cotoneasters are also popular. Outstanding autumn leaf colour is also produced by cherries, rowan, Nyssa, American sweet gum (Liquidambar), Cercidiphyllum, the fallen leaves of which smell like burnt sugar, and scarlet oaks. There is also a surprisingly large number of herbaceous plants capable of providing good colour.
Some years are better than others for autumn leaf colour and some gardens are more suitable, especially those with moisture-retentive loams and a moist climate. Even domestic gardens can display beautiful autumn colours. Get the right weather and timing, and the colour of beech, oak, elder, spindle and viburnums can rival the maples of New England in the fall.
Where to see autumn colour
The following are some of the places in Cornwall where autumn leaf colour can be seen, the exact dates depending very much on the weather. It is also advisable to check the opening dates and times.
Gardens open all year round
Cotehele in the Tamar Valley (National Trust) - a valley woodland garden of outstanding beauty and interest.
Lanhydrock near Bodmin (National Trust) - both the gardens and parkland provide year-round interest.
Pine Lodge, Holmbush, near St Austell - developed by Ray and Shirley Clemo into a 25-acre plant 'paradise', brimming over with quality plants in
Mount Edgcumbe Country Park, Cremyll, Torpoint (Cornwall County and Plymouth City Councils) - 865 acres of garden and parkland on Rame Head with spectacular views.
Trebah near Helford Passage - a famous sub-tropical valley garden leading down to the Helford River, revitalised by Major Hibbert.
Trelissick, overlooking the River Fal between Truro and Falmouth (National Trust) - a beautiful setting and mild climate, with 230 acres of garden, sheltered by 375 acres of woodland and parkland.
Trevarno Estate Gardens, Crowntown, near Helston - Victorian and Georgian gardens and subtropical plantings.
Nurseries with gardens open all year
Burncoose Garden and Nursery, Gwennap, near Redruth - a 30-acre woodland garden and a nursery, offering more than 3,000 plants, as well as many rare and unusual collectors' items.
Japanese Garden and Bonsai Nursery, St Mawgan, Newquay - a nursery with an authentic Japanese garden of over an acre.
Gardens open until the end of October
Marsh Villa Gardens, Par - 3 acres of garden rooms, plus a wild garden and marshy area. open Sun-Weds.
Trengwainton near Penzance (National Trust) - a stream, woodland and walled gardens that provide habitats for some plants not grown elsewhere on mainland Britain.
Glendurgan beside the Helford River (National Trust) - a valley garden noted for its trees and exotic shrubs, especially in the spring, but providing interest and colour into late autumn.
For more comprehensive lists of gardens open, contact William Croggon, NGS County Organiser for Cornwall (01872 530372; visit the National Gardens Scheme at www.ngs.org.uk; look out for the Cornwall Gardens Guide (01872 322900; or visit www.gardensofcornwall.com.
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