Nature hit snooze button on foliage, just now starting to pop

Oak foliage is turning red this fall.
Oak foliage is turning red this fall. (Sandra Leavitt Lerner)
By Joel M. Lerner
Friday, October 22, 2010; 9:30 AM

The beginning of autumn leaf color has been fickle this fall, perhaps because trees and shrubs were growing beyond their heat and drought tolerances this year. But, as moisture and cool temperatures return, leaf peepers will have a beautiful autumn, just a little later than usual. Chlorophyll production in the foliage has begun to slow, and the leaves are finally starting to show some of their other hues.

The green colors are yielding to oranges (carotenes) and yellows (xanthophylls) that are part of the pigment already in the leaf. Reds (anthocyanins) form in fall, and this tendency has been bred into many trees to give them a showier appearance. For example, a seed-grown red maple (Acer rubrum) is a native plant that will not have dependable red fall foliage but will often be a dull yellow. So, plant scientists bred varieties like the October glory red maple, which can dependably produce anthocyanins for a showier appearance.

My personal preferences are red-to-maroon fall foliage. There are many trees and shrubs that offer these hues from seed-grown stock. Some of my favorites are sweetgum (Liquidambar styraciflua), black gum (Nyssa sylvatica), scarlet oak (Quercus rubra), Virginia sweetspire (Itea virginica), flame azalea (Rhododendron calendulaceum), trident maple (Acer buergerianum), amur maple (Acer ginnala), sassafras (S. albinum), flameleaf sumac (Rhus copallina) and highbush blueberry (Vaccinium corymbosum).

Will we have brilliant colors from all these trees and shrubs this fall? It's impossible to know, but I predict that species of trees will peak at different times, depending on soil moisture and their protection from this season's record heat. In all probability, the showy reds, oranges, and yellows will not hold for long this season.

Here's my personally researched autumn leaf report on the local foliage conditions this season, including the showiest and most disappointing trees as well as some colorful shrubs. Use this as a guide to pick your colors of choice if you are selecting plants for your garden for 2011.

Successes

Sweetgums are actually not gum trees; they are members of the witch hazel family. Their long-lasting fall leaves persist into late autumn. The foliage will hold its deep red, maroon leaves almost until winter.

Dawn redwoods and baldcypresses are conifers that wouldn't be thought of as deciduous trees, but their needles are still turning a beautiful russet-red color.

Red maples that colored red this year were the hybrids. The seed-grown varieties did disappoint this year, as they do most years, with brownish-yellow foliage. Generally, you can only count on known hybrids that you purchase at garden centers. Buy your tree now to know what color it will turn in the fall.

Japanese maples are enjoyed for their maroon foliage throughout the entire growing season. The only drawback of those hybrids is that many do not offer a fall color display. The leaves change from red to brown. The species displayed green leaves this summer, and some already turned brilliant pink-to-orange this fall.

Flowering pears are slowly coloring into a shiny maroon hue, and despite the trees' tendency to split in heavy winds, they haven't disappointed leaf peepers. But they don't color evenly - many have mixed green and maroon foliage at the same time.

Oxydendrons' main attribute is their summer flower. However, their showy orange-red fall color is well worth the wait.

Forsythias seldom have a fall foliage colorful display. I've only noticed it several times. This year, the yellowing leaves are turning almost purple as they persist on the stems into late October.

Crape myrtles' leaves were beautiful this fall. Although they are generally grown for their flowers all summer, the foliage that I have seen so far is a reddish-bronze and making a beautiful show.

Poison ivy is rarely desirable, but the orange-red leaves of this woody-stemmed vine are quite ornamental. It was showier this year than many other years. It adds an aesthetically pleasing element to the trunks of trees and is a standout in woodland and sunny areas.

Disappointments

Hickories typically change from green to a brilliant yellow that almost makes them glow but they then turn brown rather quickly. This year, they are displaying all leaf colors at the same time and are not very ornamental with the simultaneous mixed green, yellow and brown foliage.

Black gums haven't provided much of a show this season. They are usually brilliant red throughout fall. My hunch is that many of the black gums were drought-stressed pretty severely by August, which is why they were dropping their leaves as they started to turn red this fall.

Common dogwoods turn a dependable maroon color in autumn, but this year the color change began fairly early. The foliage on most dogwoods wilted by the time they started to change color. By early fall, they were already dropping leaves.

Sugar maples are celebrated for their syrup and equally well known for fall foliage in New England. Washingtonians still try to grow them, but it is too hot and humid here for sugar maples to grow vigorously and display the colors that wash over the mountains in New England. These trees are not suited for this climate.

Tulip poplars simply defoliated in September and early October , when their foliage turned a drought-related yellow. Then, during wind and rainstorms, they dropped most of their leaves about a month early, an early leaf loss that was a protective measure against drought.

Common witch hazels have some of the most dependable yellow- and maroon-colored foliage in woodland areas. They were a lackluster yellow this fall. They still might be yellow, depending on weather conditions.

Burkwood viburnums are usually turning a rich maroon color at this time of year, but they turn very slowly. They are a mixed maroon and green this year, but in a protected environment the leaves will stay green and hold for a long time, often into winter. It depends on the microclimate in which they are growing.

Microclimate and day length are the greatest factors in the way in which a plant grows. Therefore, your observations might differ from mine depending on exactly where your plants are sited. Take the time to observe these additional characteristics that will add another season of interest to your garden.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.


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