By late August or early September, the first trees begin to change into their autumn attire. Weather conditions and microclimates determine how the ‘Indian Summer’ unfolds each year. This is the period when most deciduous trees display an abundance of colors—creating a visual spectacle in clear, sunny weather. Cold daytime temperatures can make the colors even more vivid. Curious how you can bring those striking colors into your own design? Keep reading. In this blog, we’ll explain how these autumn hues arise and why fall colors can never be fully guaranteed.
The Technical Story
The often breathtaking colors of autumn trees are the result of complex biochemical processes. These processes are closely linked to the changing seasons and are especially visible in deciduous trees. Understanding them makes it easier to select trees based on their autumn colors. Below are some key terms and aspects:
- Breakdown of chlorophyll: As days grow shorter and temperatures drop, deciduous trees receive signals to prepare for winter. This triggers the breakdown of chlorophyll, which reveals the hidden pigments in the leaves. Chlorophyll is the green pigment that makes photosynthesis possible and dominates leaf color in spring and summer.
- Production of anthocyanins: In some tree species, such as maples (Acer sp.) and dogwoods (Cornus), the breakdown of chlorophyll allows another group of pigments anthocyanins to shine through. These give leaves their red, purple, and burgundy tones. The intensity depends on the pigment concentration, as well as environmental factors like temperature and light. Of these, light intensity plays the biggest role in how we perceive the colors.
- Carotenoid pigments: These pigments are responsible for the yellow and orange tones in leaves and are present year-round. They are usually masked by chlorophyll, but once chlorophyll breaks down, they become visible. Carotenoids create the golden and orange colors we see in trees and shrubs. They are also visible underground, for example in carrots, where green pigments are absent.
Not all trees change color in the same way. Broadly speaking, trees that produce leaves only in spring, such as maples (Acer), start changing color from the outside of the crown inward. Trees that produce new leaves throughout the growing season, such as birches (Betula) and larch (Larix), start changing from the center outward. Some species, like alder (Alnus glutinosa) and common ash (Fraxinus excelsior), barely show fall colors and often drop their leaves while still green. Others within the ash family, like Fraxinus pennsylvanica ‘Summit’ and Fraxinus americana ‘Autumn Applause,’ are famous for their vibrant displays.
Microclimates and Weather Conditions
Several environmental factors strongly influence the autumn colors of trees: daytime and nighttime temperatures, soil type and moisture, humidity, and light intensity. Weather in the preceding summer also matters, whether it was warm and dry or cool and wet and whether the transition to colder weather is sudden or gradual.
In general, warm sunny days followed by cool, crisp nights create the most stunning colors. Dry weather also helps, since too much rain can wash out pigments. Wind, of course, simply blows the leaves away. The best ‘Indian Summer’ occurs in dry, clear conditions.
Because these factors vary every year, autumn color can never be guaranteed. Even if a tree shows brilliant red at the nursery, that same color may not appear in your garden. Genetic variation also plays a role, seed-grown trees of the same species may turn different shades of red, orange, or yellow. For example, a Parrotia selected for its red tones may turn out more orange or yellow. While there’s no guarantee, selecting trees during autumn does increase your chances of getting the color you want. Ultimately, light and how strongly it shines, plays a major role in how we experience fall colors. On a gray autumn day, even the brightest trees will look dull.
Goodbye Summer, Hello ‘Indian Summer’
The term ‘Indian Summer’ originates in North America, referring to the time when Native Americans would go hunting. Today, it describes a spell of pleasant autumn weather following an earlier cold period—and for many, it has become more of a nature experience. The low sun sets the trees ablaze. Autumn at its finest.
A Few Favorites
Warm golden yellow: Betula nigra, Carya cordiformis, Carya illinoinensis, Cladrastis kentukea, Juglans nigra
Light yellow: Styphnolobium japonicum, Gymnocladus dioica, Fraxinus pennsylvanica ‘Summit’, Celtis sinensis, Phellodendron amurense
Orange: Acer triflorum, Zanthoxylum simulans, Crataegus x persimilis ‘Splendens’, Koelreuteria paniculata, Pyrus calleryana ‘Chanticleer’
Fiery red: Acer x freemanii ‘Autumn Blaze’, Ulmus ‘Frontier’, Parrotia persica, Acer truncatum ‘Pacific Sunset’, Nyssa sylvatica
Bronze red: Quercus imbricaria, Quercus phellos, Quercus palustris, Zelkova serrata
Red-violet: Fraxinus americana ‘Autumn Applause’, Nyssa sinensis, Parrotia persica ‘Bella’
Conclusion
Selecting the perfect tree with dazzling autumn colors is about more than just choosing a species. To achieve the most spectacular effect, you need to consider soil type, moisture, microclimate, available space, and the specific hues you want. Whatever species you choose, taking the time to select a tree in its autumn colors will give you the best chance at creating the vibrant fall landscape you envision.
