We're heading for an autumn of unparalleled colour — but why?

Japanese maple (Acer palmatum) tree backlit in late autumn light, Ramster gardens, Surrey, England, UK. October. — It's hard to beat the autumn hues of a Japanese maple.

(Image credit: Naturepl.com/Tim Edwards)

Glorious leaf colours are one of the joys of autumn. They fill our landscapes and gardens with red, orange and yellow — colours unknown in summer. Yes, the process is actually a by-product of the leaves dying, but it also serves a definite evolutionary purpose and brightens our way from summer sunshine to winter gloom. Autumn colour is a time to celebrate.

Why and how do trees and shrubs do it? The ‘why’ question is easy to answer. Trees started to evolve about 390 million years ago. All were evergreen and operated in warm, sunny climates. The emergence of deciduous plants about 135 million years ago was a logical development. They learnt to shed their leaves so that they could survive in cold areas with long, dark winters.

However, that does not explain why the dying leaves take on such brilliant colours. Everyone knows that leaves are green because they contain chlorophyll — a photosynthesiser that uses the sun to create the foods, mainly sugars, that plants require to live and grow — but other colours are present in foliage that are overpowered by chlorophyll’s green. Autumn’s hues come from useful flavonols and carotenes — respectively yellow and orange — and, later in the season, from red anthocyanins, which are a by-product of change. These compounds, and their colours, occur all through the vegetable kingdom, not only leaves: raspberries contain anthocyanins; yellow raspberries are dominated by a carotene called lutein.

Rydal Water, a lake surrounded by autumn-shaded trees, glows in the late summer sun — Rydal Water in the Lake District glows in the autumn sunlight.

Chlorophyll does not live forever. Scientists tell us that the individual chloroplasts break down and are constantly replaced throughout the summer. However, as autumn approaches, rather less green chlorophyll is recycled, so the underlying colour of the leaves is revealed. Some leaves turn pure yellow and others mainly red, with endless variations in between. The exact mixture of these compound chemicals varies between individual plants, as well as between species — hence the degree of yellow or red colouring in the dying leaves. An important part of the process is called abscission: the tree or shrub starts to lay down a layer of cork where the leaves are attached to the branches and, eventually, the leaves fall off.

Frost accelerates the process. The best autumn colour comes from hot, sunny days and cold, cloudless nights — what we call an Indian summer. If autumn is mild and wet, the process slows down and enough chlorophyll survives to mix with the reds so that the leaves appear brown. Most of us had a hot and sunny summer. Provided we have cold nights, autumn colour this year will be all the better for it. That said, the leaves of our red maples Acer rubrum and scarlet oaks Quercus coccinea will never match the splendour of those in New England and Canada because our summers — even this one — are cooler than theirs and our autumns usually damper.

'The process is gradual and individual leaves die by stages, so a tree will have leaves of many changing hues as autumn progresses'

You can see the carotenes in such trees as poplars, ginkgos and birches, each of which turns to a distinct and uniform shade of brilliant yellow or gold, but without even the merest hint of the reds that come from anthocyanins. Not all trees and shrubs make anthocyanins. Unlike the ever-useful carotenes — which help with photosynthesis — anthocyanins are not present in the leaf throughout the growing season, but a sign that the sugars are breaking down in the presence of bright sunlight. Japanese maples, liquidambars and rowans are some of the best — the most dependable — trees for good leaf colour in our climate.

Anthocyanins have another significant purpose: when the leaves fall to the ground they inhibit the development of rival plants. The technical term is allelopathy. Walnut trees and sycamore are good examples, but so are the tree of heaven Ailanthus altis-sima and the Canadian sugar maple Acer saccharum: they keep their competitiveness by killing off their rivals.

Trees are a rich shade of orange, red and brown, surrounding a lake and pantheon in Stourhead, Wiltshire — A classical framing: A visit to Stourhead is essential to see the rich autumn colours at their best.

How long does autumn colour last? It varies between species. The tupelo Nyssa sylvatica may hold its brilliant scarlet colour for a week or 10 days, but the sweetgum Liquidambar styraciflua retains its autumn leaves for up to six weeks. The process is gradual and individual leaves die by stages, so a tree will have leaves of many changing hues as autumn progresses.

Hot, dry weather can also bring on a change of leaf colour. If you saw birch trees turning yellow in August, it’s because they are surface-rooting and suffered more than most trees from the heat and drought of summer. Their survival strategy is to shut down prematurely.

Japanese maples and cherries are among the first to show their autumn colour. Normally we have to wait a couple of weeks before our native trees start to turn. The beechwoods of the Chilterns and the oakwoods of Sherwood and Savernake are at their best in early November. The brown tinge to their leaves comes from tannins left inside when the chlorophyll fades away; they overwhelm the carotenes.

Elm trees are among the last to turn colour and drop their leaves. Young beeches and hornbeams hold onto their dead leaves until spring. Marcescence is the scientific word for this phenomenon and there are many reasons for it — but that is another story.

This feature originally appeared in the September 9, 2026, issue of Country Life. Click here for more information on how to subscribe

Charles Quest-Ritson is a historian and writer about plants and gardens. His books include The English Garden: A Social History; Gardens of Europe; and Ninfa: The Most Romantic Garden in the World. He is a great enthusiast for roses — he wrote the RHS Encyclopedia of Roses jointly with his wife Brigid and spent five years writing his definitive Climbing Roses of the World (descriptions of 1,6oo varieties!). Food is another passion: he was the first Englishman to qualify as an olive oil taster in accordance with EU norms. He has lectured in five languages and in all six continents except Antarctica, where he missed his chance when his son-in-law was Governor of the Falkland Islands.