By Wendy Diaz EMGV
One thing I especially love about North Carolina, as a native of Canada, is that it has mild winters and yet we also experience four distinct seasons. I can still enjoy the seasonal changes that I have grown accustomed to as a child. Of particular joy for me is the fleeting period in the fall when the green foliage of the deciduous forest dramatically changes to bright warm colors. Is it just me or are the fall colors more vibrant in the Triangle this year? The autumn display reminded me of my youthful memories of the orange and brilliant colors of southern Ontario[1] especially against our brilliant blue Carolina sky.
Rich Native Color: Yellow, Gold, Orange, Red, Burgundy and Copper
As I transition to a native garden and strive for more year-round interest in my landscape, I have been paying closer attention to the fall color of the plants I purchase. Formerly, fall color was a neglected dimension in my garden landscape as I focused on planting evergreen screens and summer flowers. I wanted to try to add more orange and reds reminiscent of the sugar maples of my youth so I have planted Fothergilla ‘Mount Airy’ and transplanted some ‘volunteer’ Red Maples (Acer rubrum) and Flowering Dogwoods (Cornus florida). Fortunately, North Carolina has an abundant variety of tree, shrub and herbaceous plant species the provide spectacular color in the autumn.
I also transplanted some Winged sumac (Rhus copallinium) next to my sitting bench from the woodland natural area in my yard.
With large trees of American Beech (Fagus grandifolia), Hickory (Carya cordiformis), White Oak (Quercus alba), Eastern Redbud (Cercis canadensis), Sweet Gum (Liquidamba styraciflua) and Red Oak (Quercus rubra), I already had plenty of gold, yellow and golden brown with some dark red colors to view in my yard.
American Beech (Photo taken on November 11, 2018) , Eastern Redbud leaves with Muhly Grass (Muhlenbergia capillaris ‘White Cloud’; fall blooms not leaf color, photo taken November 10, 2021), Hickory and White Oak canopy (photo taken on November 15, 2021) and Red Oak (photo taken on December 4, 2020). Photos by Wendy Diaz
Collection of fall leaves from my yard. Sourwood, Sweet gum, Beech, Red Oak, Dogwood, Red Maple and Blueberry, Photo taken November 24, 2020. Black Gum (Nyssa sylvatica) seedling; photo taken November 9, 2021
A Black Gum tree (Nyssa sylvatica) tree in my backyard died during a dry period in 2019 but recently I saw a small seedling nearby and I hope it will grow up tall so I can see its brilliant orange oval leaves from my office window in a few years. I transplanted Red Maple seedlings in front of a grove of Hickory trees to obtain some layering and depth in my narrow back yard during autumn. In 2020, I purchased and planted a Sourwood (Oxydendrum arboreum) seedling for more color in our small front yard. The occasional evergreen Red Cedar (Juniperus virginiana) and Magnolia (Magnolia grandiflora) trees provide a bright green contrast to fall colors of the deciduous trees and seem to make the fall colors stand out in the woodland landscape[2].
There are a variety of native trees shrubs that grow well in the Piedmont that are beautiful in the fall like Blueberry (Vaccinium corymbosum), Virginia Sweetspire (Itea virginica) and my favorite Oakleaf Hydrangea (Hydrangea quercifolia).
Blueberry bush under Loblolly Pine, photo taken December 2, 2020. Closeup of blueberry leaves turning from green to yellow and orangey red, photo taken November 28, 2020. Brilliant orange, yellow and unique burgundy colors of Oakleaf Hydrangea, photo taken November 24, 2020. Range of leaf color on Oakleaf Hydrangea bush at one time, photo taken November 27, 2020. Oakleaf Hydrangea in foreground and American Beech in background of photo taken November 24, 2021. Photos by Wendy Diaz
Several years ago, I pulled off some invasive vines from a thicket of Arrowwood (Viburnum dentatum) and now I am treated in the morning light with a view of the coppery shimmer of the arrowwood’s leaves.
Arrowwood thicket in the morning light, photo taken November 21, 2021. Closeup of copper brown color of Arrowwood leaves, photo taken December 2, 2020 and morning light shining through copper colored leaves of arrowood, photo taken November 18, 2021.
Also, outstanding fall color can be obtained in your home landscape by planting such native herbaceous perennials as Amsonia (Amsonia hubrichtii), New York Ironweed (Vernonia noveboracensis; actually seed heads have the color not foliage), Virginia Creeper (Parthenocissus quinquefolia) and even Scarlet Rose Mallow (Hibiscus coccineus) puts on a vibrant display.
Why causes leaves change color?
In the autumn when the temperature cools and the days are shorter it triggers the leaves to change color. Through a process called senescence the plant goes dormant at the end of the growing season and the leaves begin to die[3]. Leaves contain pigments that absorb light and certain pigments absorb different wavelengths of light. Most of the pigments in the deciduous leaf are chlorophyll a and chlorophyll b and absorb light in the violet, blue and red wavelengths of light and reflect back green wavelengths which we see in the spring and fall. Leaves also contain carotenoids (including carotene and xanthophyll), another class of pigments[4]. The underlying orange and yellow carotenoids reveal themselves after the chlorophyll pigment breaks down first in the leaf in response to cooler temperatures. Red colors are produced by anthocyanins and trees that have red fall leaves contain anthocyanin pigments. Yellow leaves contain mostly xanthophyll pigments, orange leaves contain carotene pigments but only are visible after the chlorophyll fades. Like chlorophyll these pigments are produced in the spring but anthocyanins are produced at the beginning of the fall. Cooler temperatures make the sap viscosity increase and tougher for water to be transported throughout the tree and this helps sugars build up in the leaves which triggers the production of more anthocyanins[5]. Color depends on environmental factors so color brilliance can vary a lot. Factors like the number of clear cold nights, sunny days and rainfall and the timing of the first freeze all affect fall color intensity so even if you expect to have a brilliant orange or red maple every year you may not, if the growing season environmental conditions were not ideal and included a drought or early freeze. Generally, the most vivid colors occur when there are cool nights and sunny days starting in September. This explains the especially vibrant fall display this year in the Triangle because we have had a dry fall with our fair share of cool nights and clear blue skies.
Remember to keep (rake them off your grass and put them under a tree) or leave your leaves where they fall as they provide nutrients for your trees and provide shelter for many insects that birds need for food[6]. Leave your leaf groundcover and conserve this valuable natural resource[7] and if you live in Durham don’t forget to make the pledge to keep your leaves[8]. I hope you had a chance to enjoy our bright fall color display in the Piedmont this year while working in your own yard or walking in the deciduous forest nearby.
[1] Fothergilla ‘Mt Airy’ – Spectacular Orange Autumn Color – Southern Style
[2] Using Fall Color in Your Landscape Design by John Monroe former owner of Architectural Trees Triangle Gardener September-October 2016 page 15
[3] https://content.ces.ncsu.edu/extension-gardener-handbook/glossary
[4] How Plants Use Light for More Than Just Energy by Matt Jones, Horticulture Extension Agent of Chatham County Center Triangle Gardener September-October 2019 page 24
[5] https://climate.ncsu.edu/blog/2019/10/the-leaves-they-are-a-changin-but-why/
[6] https://durhammastergardeners.com/2021/11/17/leave-your-leaves/
[7] To leave or Not to Leave November 15, 2021 WDD https://durhammastergardeners.com/2015/11/
[8] https://keepdurhambeautiful.org/pledge-to-leave-your-leaves