Marc Montefusco
Frederick County Master Gardener Program

Fall leaf color is determined by a combination of environmental conditions and genetic predisposition. Put another way, if the shrub or tree you're growing doesn't have the basic chemistry to produce colorful leaves in the fall, nothing you can do will change that. Horticulturists spend a lot of time breeding and selecting plant varieties for fall color, but even the most colorful clone won't perform well if conditions aren't right.

Leaf color changes are triggered by a combination of shortening day length and cooler temperatures, neither of which we gardeners can control. Day length, of course, is a known factor, but early cool spells can also mean an early color season. These changes in light and temperature shut down the interface between the leaf and the rest of the plant.

The green pigment chlorophyll, which is the essential ingredient in the plant's ability to turn sunlight into stored energy, begins to break down, revealing other pigments which have been there all along. These pigments include carotenoids (the same type of chemical that makes carrots orange) and xanthophylls (which simply means "leaf yellow"). Anthocyanin is produced by trees and shrubs which manufacture a great deal of sugar, like some maples, and is responsible for the brilliants reds of early autumn.

As anthocyanin in turn breaks down, it reveals still more color in the dying leaf. Drought tends to reduce the amount of sugar a plant produces, which reduces the amount of anthocyanin, and results in a duller fall. It's a complicated equation, though, and fall color predictions are notoriously inaccurate. This is where the finger-crossing comes in handy.

The size and character of your own landscape will determine which woody plants can give you the best chance for fall color. In the native Northeast landscape, maples are the great color artists, especially red maples (Acer rubrum). Almost any red maple will give you some fall color, but there are a number of varieties available that promise spectacular results (and we all know how accurate those plant catalogs are!) Try "Red Sunset " or "Autumn Flame".

The genus Fothergilla, another northeastern native, provides spectacular fall color on a much smaller scale - red maples can reach well over 50', but Fothergilla is a spring-flowering shrub that rarely reaches 10', depending on species and variety. There are a number of cultivars on the market, but "Mt. Airy" is one of the best, and is widely available. Delicious flower fragrance is another benefit of this desirable shrub. Itea virginica, known as Virginia sweetspire, is also a native. The glossy leaves of cultivar "Henry's Garnet" turn a rich mahogany in fall, and are reason enough to grow the plant even if it didn't produce drooping 6" spires of tiny white flowers in early summer.

The witch hazels are another multi-season treat, with early flowering, fragrant blooms and good fall color that seems to be very moisture dependent (this is not a good year for witch hazel leaf color). Hamamelis x intermedia, a hybrid between H. japonica and H. mollis, is most commonly found in nurseries in a number of varieties. "Jelena," "Arnold Promise," and "Diane" provide orange, yellow, and red flowers respectively. Viburnums, usually grown for their flowers, often reveal strong muted fall colors as well, in tones of red, burgundy, and faded orange. The list could go on, but it's fun to make your own discoveries. As always, a seasonal prowl through local public gardens and arboreta will reveal the best fall performers for your area.

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