Article
Why leaves turn red and yellow in fall, and which native trees give each color
Why fall leaves turn yellow, orange or red, what the red protects, how frost, drought and a warm fall change the show, and which native trees give each color.
On this page
Yellow and orange were in the leaf all summerWhy a tree spends sugar on red leavesHow the weather makes a bright fall or a dull oneWhy two trees of one species turn different colorsNative trees and shrubs we sell, by fall colorCommon questionsSourcesLeaves turn yellow and orange in fall because the tree takes its green chlorophyll apart, and the carotenoids that were in the leaf all summer show through. Red and purple come from anthocyanins, pigments many trees make new in the last weeks from sugar held in the leaf. The best-supported explanation is that the red shades the leaf while the tree pulls nitrogen out of it. Warm, sunny days and cool nights above freezing give the most red. Genes, seed source, soil and light make two trees of one species color differently.
Yellow and orange were in the leaf all summer
A summer leaf holds two families of pigment: green chlorophyll, which captures light, and yellow to orange carotenoids, the pigments that color a carrot. For most of the year the green masks the carotenoids. The change comes with shorter days and falling temperatures, which end the leaf’s food-making and break its chlorophyll down.
Once the chlorophyll is gone, a leaf with little else in it turns yellow or gold. Hickory, birch, beech, sycamore and certain maples are among the yellows and oranges of Pennsylvania’s woods. Witch hazel turns yellow the same way. Many oaks turn mostly brown instead, as compounds in the dying cells darken. Young oaks and beeches often hold those brown leaves through winter, a habit called marcescence.
Why a tree spends sugar on red leaves
Red is different, because anthocyanins are not waiting under the green. Only the red pigments are built new in autumn, from sugar, in the same weeks the tree is emptying the leaf. Why a tree pays for pigment in a leaf it is about to drop is an old question and still a debated one. Young spring leaves use the same pigment for a related job, the subject of why new leaves come out red.
A sunscreen while the nitrogen moves out
A leaf being taken apart still absorbs sunlight but can no longer use all of it, and the surplus energy damages the leaf, most of all on bright, cold days. The resorption protection idea holds that the red pigment screens that light while the tree recovers the leaf’s nitrogen. The recovery matters, because what comes back from dying leaves can supply most of the nitrogen and phosphorus a tree stores for winter.
In 2003 researchers at the University of Wisconsin tested the idea on three shrubs: red-osier dogwood, a blueberry and a viburnum. Each came in a normal form and in a mutant that makes almost no anthocyanin. Outdoors, the mutants recovered 39 to 61 percent of their leaf nitrogen, against 73 to 79 percent for the normal plants. Under bright light and cold the difference was starker:
“mutant leaves dropped while still green and displayed signs of irreversible photooxidative damage” (Hoch, Singsaas and McCown, Resorption Protection. Anthocyanins Facilitate Nutrient Recovery in Autumn by Shielding Leaves from Potentially Damaging Light Levels, 2003)
The same tests included paper birch, which makes no red in autumn. It recovered as much nitrogen as the best of the red species, so red is one way to protect a leaf in its last weeks, not the only one.
A signal to insects, still unproven
In 2000 and 2001, Marco Archetti, and then W. D. Hamilton with S. P. Brown, proposed a different reason. Bright autumn color, they argued, signals a tree’s defensive strength to aphids looking for a host in autumn. The trees with the most intense color would then be colonized least.
Field surveys have found fewer aphids on more colorful trees, but a correlation like that is open to other explanations. When Martin Schaefer and Gregor Rolshausen of the University of Freiburg colored the leaves of same-aged European mountain ash red or green, winged aphids settled on both alike. A 2015 red maple study still counted the signal as one theory among several, against decades of accumulating evidence for red as a light shield.
The evidence so far divides this way:
- Settled. Fall red is made new, from sugar, in leaves the tree is emptying, and in the shrubs tested it protected the nitrogen salvage.
- Not settled. Whether that protection is why red evolved remains open, and so does whether the color also warns insects.
How the weather makes a bright fall or a dull one
Day length and falling temperatures set the start. In 18 years of records from Harvard Forest in Massachusetts, color began around the start of September, peaked in October and lasted into November. A model built on day length and accumulated cool weather explained most of its timing.
Sugar trapped behind the abscission layer
Weather decides how much red there is. As the colors change, the tree builds an abscission layer across the base of each leaf stalk. It is a zone of cells that gradually severs the tissues holding the leaf, and the tree seals the twig side as it goes. The weather traps sugar in the leaf:
“The warm sunny days increase the sugar production in leaves, while cool nights slow the movement of these sugars through narrowing leaf veins and petioles.” (University of Wisconsin Arboretum, Fall Color, Weather, and Forecasts)
Sugar held in the leaf becomes anthocyanin. Low temperatures above freezing favor anthocyanin, while an early frost weakens the red. The best conditions for color are bright days, cold nights above freezing and dry weather short of drought.
Frost, drought and a warm, wet fall
Three kinds of weather spoil a year:
- An early hard freeze. It kills leaves before they finish changing, and it cuts off the red, which the leaf is still making.
- Drought with heat. A month of rainfall 25 to 75 percent below normal and near-record heat hit Pennsylvania in 2019. Color came early and muted, and leaves dropped early, before the mid-October peak.
- A warm, wet fall. Unusually warm weather into mid-October 2021 was expected to delay and somewhat diminish Pennsylvania’s display. The very wet summer before it could increase leaf-spotting fungus, which can also dull color in places.
Drought does not always mean early color: summer drought can delay it, while trees in poor health often color early. At Harvard Forest a warmer September went with later color and later leaf fall, and warmer years tended to bring a longer display, not a shorter one.
Why two trees of one species turn different colors
Part of the difference is inherited. In a study of 27 red maples in Ontario, the trees differed widely in how red they turned, and each tree’s anthocyanin level held steady between the two years of the study. Seed source matters as well: red maples in the north of the range show the most reddish autumn color. Blue Whale Trees grows its plants from seed rather than from cuttings, so each sapling carries its own mix of genes and may not match its neighbor’s shade.
Soil and light count too: in the Ontario maples, the timing of color and the amount of red tracked soil pH and how open the canopy was. In a Forest Service study of 16 sugar maples, leaves lower in nitrogen through the season colored better, a pattern the authors tied to stress promoting red and early leaf aging.
The same effects show species by species. Black gum prefers acid soil and turns yellow on limestone. Sourwood and American hornbeam color best in sun. American smoketree colors better in lean, dry soil than in a pampered bed.
A tree that colors weeks ahead of others of its kind may be short of water or in decline. For a tree in its first year, the watering calculator gives the gallons for each watering and how often.
Native trees and shrubs we sell, by fall color
Four tables, one for each color, give each plant’s fall color, when it turns and its mature height, tallest first. A blank means no source gives the timing. The pigment mix sets a species’ color:
“Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.” (SUNY College of Environmental Science and Forestry, Why Leaves Change Color)
Reds and scarlets
| Plant | Fall color | Turns | Height, feet |
|---|---|---|---|
| Swamp chestnut oak | Rich red-brown | Late, with the oaks | 60–90 |
| Swamp tupelo | Red | 60–80 | |
| Nuttall oak | Deep red | Late in fall | 50–80 |
| Shumard oak | Red, often the first of the oaks | Early in fall | 50–80 |
| White oak | Wine-red | 50–80 | |
| Northern red oak | Russet to bright red | 50–75 | |
| Northern pin oak | Red | 50–70 | |
| Pin oak | Deep red | 50–70 | |
| Black gum | Blazing scarlet | From early September | 40–70 |
| Sourwood | Crimson | September | 25–50 |
| Texas red oak | Burgundy to scarlet | 20–50 | |
| Georgia plume | Bright red | 10–16 | |
| Red chokeberry | Blazing red | 6–12 | |
| Elliott’s blueberry | Scarlet, the leaves held into winter | 4–10 | |
| Black chokeberry | Red, some of the best of any shrub | 3–6 |
Oranges and orange-reds
| Plant | Fall color | Turns | Height, feet |
|---|---|---|---|
| Bald cypress | Rust-orange, before the needles drop | 50–80 | |
| Yellow buckeye | Yellow to orange | 50–75 | |
| Sassafras | Orange | Among the earliest, from mid-September | 30–60 |
| Florida maple | Yellow to orange | 20–60 | |
| Blueberry hawthorn | Brilliant orange and red | 20–50 | |
| American hornbeam | Orange to red, strongest in sun | 20–35 | |
| Chalk maple | Yellow, orange and deep red | 25–30 | |
| American smoketree | Orange, scarlet and purple at once | October | 20–30 |
| Washington hawthorn | Orange-red | 20–30 | |
| Downy serviceberry | Orange-red | Early in fall | 15–25 |
| Staghorn sumac | Fiery orange-red | Among the earliest, from mid-September | 15–25 |
| American hazelnut | Orange-red | 8–12 |
Yellows and golds
| Plant | Fall color | Turns | Height, feet |
|---|---|---|---|
| Shagbark hickory | Golden | October | 60–90 |
| Mockernut hickory | Clear gold | Mid-October, with the hickories | 60–80 |
| Bitternut hickory | Clear yellow, held longer than other hickories | Early in fall | 50–80 |
| Pignut hickory | Rich gold | Mid-October, with the hickories | 50–80 |
| Black maple | Yellow, sometimes orange and red | Earlier than sugar maple | 60–75 |
| Yellow birch | Bright golden yellow | 60–75 | |
| Tamarack | Gold, then the needles drop | 50–75 | |
| Sweet birch | Clear gold | 40–70 | |
| Yellowwood | Clear yellow | Late September to mid-October | 30–50 |
| Striped maple | Bright yellow | 15–35 | |
| Witch hazel | Golden | Late, as it blooms | 12–20 |
| Spicebush | Clear yellow | October | 6–12 |
Purples, bronzes and copper
| Plant | Fall color | Turns | Height, feet |
|---|---|---|---|
| American beech | Copper, the leaves held through winter | 50–80 | |
| Shingle oak | Russet, the leaves held through winter | 40–60 | |
| Flowering dogwood | Burgundy | Often the first red in the woods | 15–30 |
| Franklin tree | Orange, red and purple | 10–25 | |
| Nannyberry | Wine-red | 12–18 | |
| Blackhaw | Purple-red | Late, and held | 12–15 |
| Hobblebush | Bronze-red and purple | 3–12 | |
| Mapleleaf viburnum | Pink, magenta and purple | 3–6 | |
| Virginia sweetspire | Red and gold, held into early winter | 3–6 |
The catalog’s fall color filter lists these and more, among them American persimmon, cherrybark oak and shellbark hickory. The tree finder pairs the same fall color box with filters for zone, size, sun and soil moisture. Most trees in the table are among our yard trees, the hickories among the nut and fruit trees, and the shrubs among the native shrubs.
Common questions
Why is my tree changing color in August?
A tree that colors weeks ahead of others of its kind is often under stress from drought or declining health, and a young tree needs water through dry spells. Black gum and sourwood start in September by nature, and flowering dogwood is often the first red in the woods.
Does a dry summer mean poor fall color?
Not by itself, since dry weather that stops short of drought is part of the recipe for bright color. Real drought with heat brings early, muted color and early leaf drop, as Pennsylvania had in 2019.
Why did my tree’s leaves turn brown instead of red?
An early hard freeze can kill the leaves before they finish coloring. Many oaks turn mostly brown in any year, as compounds in the dying cells darken.
Will a seedling have the same fall color as its parent tree?
Not necessarily, because fall color is partly inherited and each seedling carries its own mix of genes. Its soil and light will shape the color too.
Sources
- Red Maple, Silvics of North America: USDA Forest Service: red maple’s variation across its range, with trees in the north showing the most reddish autumn color.
- Development of fall foliage color in sugar maple: USDA Forest Service: sixteen sugar maples in which leaf nitrogen ran against the quality of fall color, and stress promoting red.
- Why Leaves Change Color: SUNY College of Environmental Science and Forestry: carotenoids masked by chlorophyll, the layer that severs the leaf, the browns of oaks, and cool nights against early frost.
- Fall Color, Weather, and Forecasts: University of Wisconsin Arboretum: warm days and cool nights trapping sugar in the leaf, drought, tree health and an early hard freeze.
- Warm, wet autumn could mute and delay foliage display in Pennsylvania: Penn State: Marc Abrams on the best conditions for color, the trees behind the yellows, and a warm, wet fall.
- Extremely dry, hot conditions this fall causing early, muted foliage display: Penn State: the drought and heat of 2019 and the early, muted color and early leaf drop that followed.
- Resorption Protection. Anthocyanins Facilitate Nutrient Recovery in Autumn by Shielding Leaves from Potentially Damaging Light Levels: Hoch, Singsaas and McCown, Plant Physiology 133 (2003): the mutant test, the nitrogen at stake for winter, and paper birch.
- Aphids do not attend to leaf colour as visual signal, but to the handicap of reproductive investment: Schaefer and Rolshausen, Biology Letters 3 (2007): the signal idea, its test, and red alone made new.
- Early Autumn Senescence in Red Maple (Acer rubrum L.) Is Associated with High Leaf Anthocyanin Content: Anderson and Ryser, Plants 4 (2015): variation among 27 red maples, soil pH and canopy openness, browns from darkening phenolics, and the theories of fall red.
- Predicting Climate Change Impacts on the Amount and Duration of Autumn Colors in a New England Forest: Archetti, Richardson, O’Keefe and Delpierre, PLOS One 8 (2013): Harvard Forest records, warm Septembers delaying color, and the oaks as the last to peak.
- Fall Color: Missouri Department of Conservation: the phases of the season, sassafras and sumac among the earliest to change from mid-September, and hickories and oaks at the height of the display in mid-October.
- Nature profiles: fall color: Holden Forests and Gardens, the profiles of shagbark hickory, spicebush and American yellowwood: October for the hickory and the spicebush, late September to mid-October for the yellowwood.
- Serviceberry, Amelanchier spp.: University of Wisconsin-Madison Extension: downy serviceberry’s leaves turning yellow-orange to red early in the fall.