As the last of the leaves finally fall, Jackie Hunt, Turn End’s Gardener looks back at this year’s spectacular autumn colour.
Us gardeners love to compare how the garden is different each year. Was it a cold winter, how early or late was spring, did flowers bloom well? I have kept a diary of weekly weather conditions, what’s in flower and jobs that I undertake since I started at Turn End in 2010, which I find interesting reading an a useful planning guide.
It seems to have been a colourful and particularly leafy autumn this year. We have had a long display of gorgeous colour, including the fan-shaped Ginkgo biloba leaves that turned from fresh green to hints of butter yellow before all dropping after the first frost, leaving fresh smell like mown grass. Or Cotinus coggyria (smoke bush) whose plummy-purple foliage turns through reds and oranges in patterns that remind me of peacock feathers. Even now in mid December there are a few bronzed and curled leaves hanging bravely on at the top of the beech tree in the Daisy garden (Fagus sylvatica ‘Cockleshell’).
Looking back though my records we didn’t have a frost in early 2016, the spring was long and cool, so that many bulbs and springtime flowers appeared later than recent years. Then later spring and early summer was wet. Met Office records show that spring rainfall was 30% higher than normal in southern and eastern England, followed by above average sunshine in summer and early autumn. The Forestry Commission reported that these conditions provided a particularly good growing season for trees, enabling them to build up plenty of sugars in their leaves. Hence our fiery display this autumn and what has felt like endless weeks of creating leaf mountains and filling our compost bins to overflowing.
So what causes plants to put on their autumn display then drop their leaves before winter? Many trees and shrubs that grow in our cool temperate climate are deciduous, with broad leaves that are susceptible to winter damage. Shedding leaves helps them to conserve water and energy. Plants also know that there will be insufficient light over the winter for photosynthesis – the process that enables them to turn carbon dioxide and water into their own sugar as food, using energy from sunlight and green pigments in their leaves called chlorophyll.
As unfavorable weather approaches, hormones in the plants trigger the process of abscission whereby the leaves are actively cut-off of by specialized cells (from the Latin scindere, which means “to cut”). At the start of the abscission process, trees reabsorb valuable nutrients from their leaves and store them for later use in their roots. Chlorophyll, the pigment that gives leaves their green colour, is one of the first molecules to be broken down for its nutrients. This exposes other pigments that were previously masked by the chlorophyll, such as carotenoids, which are also used in photosynthesis to capture different wavelengths of light. These pigments give yellow, orange and red hues to autumn leaves. Anthocyanins give leaves their vivid red and purple colours and are made by plants as the days darken. They may perform some kind of light-protective role, allowing the plant to protect its leaves from light damage and extend the amount of time before they are shed. Sunny weather helps concentrate the sugars in the leaves, which speeds up the appearance of leaf colour. So early autumn’s sunny, warm days and cool nights have made the perfect conditions for this year’s spectacular display.
Well, that’s the science, rather simply explained…but here are a few examples of spectacular autumn colour at Turn End.