When we picture the upcoming Thanksgiving holiday, most of us conjure up an image filled with all the colors of autumn. Even as the temperature of the days changes from cool to crisp to cold, it's the medley of warm color tones that hold sway in our thoughts. There's orange, of course, like that of pumpkins, acorn squash and Mexican sunflowers. After that come shades of color emblematic of the autumn season; brick red, golden mustard and aubergine.
The most important factor in the onset of fall color is the length of daylight. At this time of year the amount of light diminishes with each new day. The combination of short but often warm daylight hours and the chilly nights trigger a physical change in leaf color. This year the weather conditions melded perfectly to create a classic autumn palette. The garden is awash with russet, umber, amber and dun.
The scientific explanation of autumn color is told from the perspective of chemical reactions. As the amount of light diminishes with each day, plants slow down their production of chlorophyll
which is the green pigment in the leaves. Eventually, production comes to a complete stop. Carotenoids are the yellow and gold pigments within a plant's leaves that begin to show through as the color green fades.
When the weather is right, like it has been this year, sugars are produced in leaves on warm autumn days. At the same time, the veins that run through the leaves are gradually constricted by crisp night air which prevents the sugars from moving out of the leaves and into the tree. These conditions produce anthocyanin pigments which give us the brilliant reds and purples.
To the gardener, autumn is a visual reward for the thought and effort put into the art of gardening. Depending on the plants we have chosen, the show can be a blast of one intense monochromatic tone or a kaleidoscope of autumn hues. Each leaf on the red maple Acer rubrum "October Glory" turns from green to red in progressive stages, changing every day. Within a week every leaf on the tree is a blaze of metallic scarlet.
Other trees and shrubs show their fall colors in a different manner. Each leaf changes colors at a different rate, so one leaf is part green and part hot pink while the next is pink and gold or gold and russet-red. The dogwoods, viburnums and spireas are fine examples of this mottled coloration. With an evergreen backdrop the colors stand out like neon lighting.
Plants worth the hype
Fothergilla gardenii "Mt. Airy" has become a popular plant in the last few years specifically for its intense fall foliage. The plant tag touts the spring flowers and honey scent as an added bonus. It's not a particularly handsome shrub for most of the year so plant it tucked to the side of a border. The leaf color, which lives up to the hype, will amaze you with intense yellow leaves that melt to orange then red, each leaf holding on to all three colors at once.
Once you have seen the oak-leaf hydrangea (Hydrangea quercifolia spp.) as it segues from one season to the next, you will want one for your own garden. In spring, thick green leaves emerge from bare mahogany bark. As the leaves unfold they closely resemble those of the oak tree. As autumn nights grow damp and chilly the leaves turn a deep burgundy. Even after the first frost, the leaves continue to develop a blend of burnt-orange, purple and faded green.
Every year I'm glad that I planted the garden for each of our four distinct seasons. If it was up to me I would be out in it every day with that very thought in mind, continually planting for the season that is just around the corner. While I know I'll spend many hours outside puttering in the chilly, late-fall and winter garden, the warmth of home entices me into the house to be with family and friends.
Autumn weather blurs my sense of time. Was summer only yesterday or was it a season long ago? I warmly remember weekends filled with sunlight, barbecues and neighborly get-togethers celebrating the heat of summer days. Thanksgiving will be the first gathering spent mostly indoors. I only hope the day is warm enough to leave the curtains open wide for a final view of the autumn garden. If it's chilly, I will light a fire to fill the house with warmth and celebrate all the glorious colors of fall.