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A Fall Garden Colour Primer

...Autumn Magic
by Janet Davis
by Janet Davis

email: beautifulbotany@sympatico.ca

Janet Davis is a freelance garden writer and horticultural photographer whose stories and images have been featured in numerous publications. Magazines featuring her work include Canadian Gardening, Canadian Living, Gardening Life, President’s Choice Magazine, Chatelaine Gardens and, in the United States, Fine Gardening and Country Living Gardener.

Visit http://www.beautifulbotany.com


October 20, 2002

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In a part of the world where autumn produces such dramatic changes in the foliage color of numerous shrubs, trees and even some perennials, it mystifies me why more people don't exploit this spectacular phenomenon in their gardens. I don't mean plopping in an otherwise boring plant for the sake of a few weeks of October fireworks -- that would be silly. But if you can have both spring flowers and red-orange autumn color, why not consider a serviceberry over a mock orange, for example?

Here's a color guide to plants whose biochemistry dictates an autumn leaf color change. Note, however, that depending on the amount of summer rainfall and sunshine, and the onset in fall of cool night temperatures, there will be annual variations in the intensity of each plant's display.

Yellow:

Trees that turn yellow/gold in autumn share this trait: their green leaf pigment, chlorophyll, breaks down to reveal, in varying degrees, the rich yellow or orange of the underlying pigments carotin and xantophyll. Yellow fall color is found in birches (Betula spp.), ginkgo trees(Ginkgo biloba), redbuds (Cercis canadensis), yellowwood trees (Cladrastis lutea), some cultivars of green ash (Fraxinus pennsylvanica) honey locust (Gleditsia triacanthos), littleleaf linden (Tilia cordata), shagbark hickory (Carya ovata), hackberry (Celtis occidentalis) and certain Norway maples (Acer platanoides). The katsura tree (Cercidiphyllum japonicum) takes on muted hues of pale yellow mixed with apricot and pink.

Shrubs with yellow/gold fall color include sweet pepperbush (Clethra alnifolia), witchhazel (Hamamelis virginiana), Cornelian cherry (Cornus mas) and spicebush (Lindera bezoin). Perennials that turn yellow include Hosta sieboldiana elegans, balloonflower and many of the meadow rues.

Red:

While it has long been know that red leaf colour in autumn derives from a number of factors including the appearance of the red pigment anthocyanin following the breakdown of chlorophyll, recent research in Vermont has focused on why trees would turn some leaves red as they are about to die. According to Paul Schaberg of the U.S. Forest Service, it appears that anthocyanin helps the trees cope with stress. Their research shows that a primary function of the pigment is to protect the tree from “photoxidative damage”. Says Schaberg: “One theory is that red is like a sunscreen that allows the leaf to linger long enough for the tree to absorb more nutrients.” The study will show that nutrient stress, particularly low nitrogen, can instigate early and more intense red color in maples. Trees with brilliant red or red/orange fall color include sugar maple (Acer saccharum), many Japanese maples (Acer palmatum), red maple (Acer rubrum), sassafras (Sassafras albidum), red oak (Quercus rubra), scarlet oak (Quercus coccinea), pin oak (Quercus palustris), black oak (Quercus velutina), some of the mountain ashes (Sorbus spp.), Washington thorn (Crataegus phaenopyrum) which colors very late, blue beech or ironwood (Carpinus caroliniana), zelkova (Zelkova serrata), wild pin cherry (Prunus pensylvanica), tupelo (Nyssa sylvatica), Sargent cherry (Prunus sargentii) and stewartia (Stewartia koreana). Ornamental pear (Pyrus calleryana) turns dull purple in fall.

Shrubs with red/orange fall color include mountain maple (Acer spicatum), Amur maple (Acer ginnala), serviceberries (Amelanchier spp.), chokeberries (Aronia spp.), burning bush (Euonymus alata), photinia (Photinia villosa), many rugosa roses (Rosa spp.), redvein enkianthus (Enkianthus campanulatus), Peking cotoneaster (Cotoneaster acutifolia), blood-twig dogwood (Cornus sanguinea), flowering dogwood (Cornus florida), Chinese dogwood (Cornus kousa), sumacs (Rhus spp.), smoke bush (Cotinus coggyria), flowering currant (Ribes aureum), arrowwood (Viburnum dentatum) and a few of the spring-flowering viburnums such as Koreanspice (V. carlesii). One of the most satisfactory fall-coloring shrubs is burning bush (Euonymus alata), which turns a spectacular cerise-pink with not a hint of orange.

Perennials that take on dependable red color include a few of the cranesbills, especially Geranium macrorrhizum and G. x cantabrigiense, and sundrops or evening primrose, Oenothera tetragona.

Good red-turning Vines are Virginia creeper (Parthenocissus quinquefolia), Engleman's ivy (P. englemannii) and Boston ivy (P. tricuspidata).

 

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