The Secret of Changing Tree Colors

In late September and early October, the trees in our yards, parks and forests begin to herald the arrival of autumn: hitherto clothed in green, they suddenly take on dazzling hues – yellows, oranges, reds and purples. So it’s a good idea to take advantage of a fine autumn day to take a family outing to the countryside, and enjoy the magnificent scenery created by the changing colors of the trees.

But don’t delay! The best of the fall color spectacle in our region, one of the richest in the world, lasts only eight to fifteen days, depending on the temperature. Strong winds, driving rain and extreme frosts shorten the display, while fine dry days followed by moderately cool nights prolong the pleasure to the maximum.

Autumn Colors: A Natural Phenomenon

But where do these brilliant colors come from? We often imagine that leaves turn colorful in autumn, but in reality it’s more a case of fading. The yellow, red and orange were already there, but were masked by the green pigmentation of chlorophyll. During the summer, chlorophyll works to absorb the energy of light rays and transform them into sugars (photosynthesis), which are then transported to the branches, trunk and roots to serve as reserves. However, when night-time temperatures remain below 7? (45?), as is the case in autumn, the sugars become trapped in the leaf and their excessive accumulation destroys the chlorophyll. It’s only then that the green color disappears, and the other pigments surface, briefly, to fill us with wonder.

Is It Because of Frost?

And what about the popular belief that frosts cause autumn coloring? There have been years when trees began to take on their autumn colors in our region, at the end of September, but most areas had not yet experienced a frost. On the contrary, the brightest colors appear when the days are warm and sunny, triggering the production of a good quantity of sugars, and the temperature always drops below 7°C (45°F) at night. Extreme cold, on the other hand, causes the leaves to die, turn brown and dull and soon fall from the tree. So, for the best autumn colors, we’re hoping for a sunny autumn with cool but not too cold nights.

If Canada is so colorful, it’s because of the mix of species in its forests. In fact, the main component of southern Quebec’s forests is the sugar maple, a tree whose autumn color is second to none. Its leaves quickly turn to various particularly fiery shades of red, yellow and orange, and remain on the twigs longer than many others. It’s the combination of this tree with other typical Quebec forest trees – including the red maple, with its pinkish-red leaves; the vinegar tree, scarlet; the ash, purple; and the birch, golden yellow – that gives the panorama all its brilliance. And the occasional pine or spruce, which maintain their dark green coats all year round, will only serve to bring out the vivid colors of the warmer trees.

What to Plant for Beautiful Colors in Your Yard?

Autumn color is often the last thing on our minds when choosing plants to beautify our grounds. The proof is that our cities are adorned with trees and shrubs that are either of little interest in autumn (crabapples, caragana, honeysuckle, etc.) or remain green until the best show is over (Norway maples, European lindens, etc.). So it’s in the countryside, not the city, that autumn colors are at their most vivid.

Nonetheless, several species with attractive autumn coloring deserve our special attention as ornamental trees or shrubs, while offering plenty of appeal in other seasons too. Here’s a list of some of these plants:

Trees

Common name	Botanical name	Zone
Allegheny Serviceberry	Amelanchier laevis	3b (4 to 8 USDA)
Paper Birch	Betula papyrifera	2 (2 to 6 USDA)
Scarlet Oak	Quercus coccinea	4 (5 to 9 USDA)
Pin Oak	Quercus palustris	4 (4 to 8 USDA)
Red Oak	Quercus rubra	4 (4 to 8 USDA)
Mountain Maple	Acer spicatum	2 (2 to 7 USDA)
Sugar Maple	Acer saccharum	4 (3 to 8 USDA)
Amur Maple	Acer tataricum subsp. ginnala	2b (3 to 8 USDA)
Red Maple	Acer rubrum	3 (4 to 9 USDA)
Tatarian Maple	Acer tataricum	2b (3 to 8 USDA)
White Ash	Fraxinus americana	3b (3 to 9 USDA)
Blue Ash	Fraxinus quadrangulata	3b (4 to 7 USDA)
Green Ash	Fraxinus pennsylvanica	2b (3 to 9 USDA)
Maidenhair tree	Ginkgo biloba	4 (3 to 8 USDA)
Ohio Buckeye	Aesculus glabra	2b (3 to 7 USDA)
European larch	Larix decidua	3b (2 to 6 USDA)
Tamarack	Larix laricina	1 (2 to 5 USDA)
Hackberry	Celtis occidentalis	4 (2 to 9 USDA)
American aspen	Populus tremuloides	1 (1 to 6 USDA)
Hop Tree	Ptelea trifoliata	3b (4 to 9 USDA)
Mountain Ash	Sorbus sp.	4 (3 to 6 USDA)

Shrubs

Common name	Botanical name	Zone
Serviceberry	Amelanchier canadensis	4 (4 to 8 USDA)
Smoketree	Cotinus coggygria	4b (4 to 8 USDA)
Bearberry	Arctostaphylos uva-ursi	1 (2 to 7 USDA)
Tatarian Dogwood	Cornus alba	2 (3 to 7 USDA)
Bloodtwig Dogwood	Cornus sanguinea	4b (4 to 7 USDA)
Cotoneaster	Cotoneaster apiculatus	4b (4 to 7 USDA)
Winged Spindle Tree	Euonymus alata	3 (4 to 8 USDA)
European Spindletree	Euonymus europaeus	4 (4 to 7 USDA)
Golden Currant	Ribes aureum	2 (3 to 7 USDA)
Common Witch Haze	Hamamelis virginiana	4b (3 to 8 USDA)
Ninebark	Physocarpus opulifolius	2b (3 to 8 USDA)
Fragrant Sumac	Rhus aromatica	3 (3 to 9 USDA)
Smooth Sumac	Rhus glabra	2b (3 to 9 USDA)
Staghorn Sumac	Rhus typhina	3 (3 to 8 USDA)
Viburnum	Viburnum sp.	2b-4 (2 to 8 USDA)

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Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on October 7, 1989.