00WHAT THE BOTANISTS SAY

The colour was
there all along.

A woodland path in autumn lined with beech and maple trees in orange, gold and red, with soft low sunlight between the trunks — AI-generated image, not a photograph of a real person or place.

Autumn takes the green away.

Green chlorophyll hides other pigments all summer. As nights lengthen it breaks down, the yellows and oranges show through, and in the right weather some trees make fresh reds.

TURNINGlate September to NovemberUpdated 14 October 2026

Check the weather

01Principles

Longer nights start it
Yellows were always there
Reds need sun and cool nights
Every autumn is a little different

02THE SHORT ANSWER

Green fades,
other colours show.

Three groups of pigments do the work.
The weather decides how bright they get.

PIGMENTS

Yellow was hiding

Forestry England says yellows and oranges come from xanthophylls and carotenoids, present in leaves all year but masked by green chlorophyll.

See the numbers

REDS

Made fresh in autumn

The US Forest Service says most anthocyanins, the reds and purples, form in autumn in response to bright light and excess sugar in the leaf.

Check the weather

LEAF FALL

A seal at the stalk

Kew explains that a seal forms at the base of each leaf, cutting off water and trapping the chemicals left inside before the leaf drops.

Why trees let go

03A QUICK WEATHER CHECK

What kind of autumn
is it this year?

Pick the weather closest to this season to see what botanists say it does to the display. The bar shows how vivid the colour is likely to be.

Based on Royal Botanic Gardens Kew, the Woodland Trust and the US Forest Service. Individual trees and species vary widely.

Autumn check

Choose the weatherSunny days and cool, frost-free nightsA warm, dry spell, then cold nightsAfter a severe summer droughtA long, warm autumnMild and wet

Sunny days and cool, frost-free nightsBrilliant

The US Forest Service says this gives the most brilliant colour: sugar builds up by day and cool nights keep it in the leaf, boosting reds and purples.

A warm, dry spell, then cold nightsBest combination

Kew calls a warm, dry spell followed by colder nights the best combination for autumn colour.

After a severe summer droughtLater

The US Forest Service says a severe summer drought, or a late spring, can delay the onset of colour by a few weeks.

A long, warm autumnMuted

The US Forest Service says warm autumn periods reduce the intensity of the colour.

Mild and wetBrown

Kew says a mild, wet autumn slows the process, so leaves often turn brown before they fall and the display is less striking.

Sources: Royal Botanic Gardens Kew, Why do leaves change colour?; US Forest Service, Science of fall colors; Woodland Trust, Why autumn leaves change colour.

04TWO NUMBERS WORTH KNOWING

A long record,
a short window.

One date for how long people have noted the seasons,
one window for when trees reach full colour.

1736

UK seasonal records go back to

The Woodland Trust's Nature's Calendar says its record of seasonal events dates back as far as 1736. Scientists use these public sightings to study how weather and climate affect timing.

NATURE'S CALENDAR · WOODLAND TRUST

Sep–Nov (sometimes Dec)

When trees reach full autumn colour

Full tinting, when almost no green is visible, can happen from late September to November and sometimes early December. Wind or frost can bring leaves down before it does.

FULL TINTING · WOODLAND TRUST

To record full tinting for Nature's Calendar, the Woodland Trust suggests finding three trees of the same species tinting at the same time, because individual trees vary widely.

05FOUR WAYS TO WATCH

Read the trees,
not the calendar.

Autumn colour is easy to watch closely once you know what is going on inside the leaf. These habits come straight from the sources.

Watch the nights draw in
The US Forest Service says lengthening nights are the most reliable trigger for colour change and leaf fall.
Notice yellow first
Yellows and oranges are already in the leaf, so they show as soon as the green breaks down.
Look for reds after bright spells
Sunny, dry weather raises sugar in the leaves, which the Woodland Trust links with redder foliage.
Compare three of a kind
Follow three trees of one species, as Nature's Calendar suggests, and record when each one reaches full tint.

Fallen leaves in yellow, red and brown covering a damp woodland floor, with leaf stalks visible — AI-generated image, not a photograph of a real person or place.

06WHY TREES LET GO

Dropping leaves
is a winter plan.

A single leaf on a branch, half green and half turning yellow and red, lit from behind by autumn sun — AI-generated image, not a photograph of a real person or place.

Before its leaves fall, Kew says a tree shuts down photosynthesis and reclaims as many valuable chemicals as it can. A seal then forms at the base of each leaf and cuts off its water.

The Woodland Trust says shedding leaves helps trees keep moisture in their branches and trunk. A leafless tree is dormant, needs less energy and copes better with winter storms.

07Questions

Questions people ask

Why do leaves turn yellow?

Forestry England says yellow and orange pigments, xanthophylls and carotenoids, are present in leaves all year. They show when green chlorophyll breaks down as the days shorten.

Why do some leaves turn red?

Red and purple come from anthocyanins. The US Forest Service says most form in autumn in response to bright light and excess sugar in the leaf, which is why sunny years tend to be redder.

What makes a good year for autumn colour?

Kew says a warm, dry spell followed by colder nights is the best combination. A mild, wet autumn slows things down and leaves often turn brown before falling.

What triggers the change?

The US Forest Service says lengthening nights are the most reliable trigger, regulating the timing of both colour change and leaf fall. Weather then affects how bright the colours are.

Why do trees drop their leaves?

The Woodland Trust says shedding leaves helps trees keep moisture in their branches and trunk and cope with winter storms. Kew adds that the tree reclaims valuable chemicals first.

08Sources

The colour was
there all along.