Seasonal Splendor – Fall at the Arboretum
While fall foliage viewing is a traditional Washington rite, for those who want to avoid the rural traffic jam of Skyline Drive, the National Arboretum offers an autumn show of everything from trees to grasses changing into their fall colors.
Many areas of the Arboretum were designed for year-round viewing, and these collections offer an opportunity to see the changes not only in the deciduous trees, but also in the shrubs, grasses, ground covers, and perennials that are impacted by the seasonal change when the green chlorophyll of summer fades to reveal the yellow and orange flavonoids, and leaves manufacture the red and purple anthocyanins that we associate with autumn.
Just as each blooming season brings subtle changes in the flowers, autumn color varies from year to year depending on changes in the climate. Autumn color is a complex physiological phenomenon dependent upon the length of night, intensity of sunlight, sugar formation in the leaf, air temperature, and for some plants, even the condition of the soil. Rainy, warm weather with little sunlight greatly reduces the development of intense fall color since anthocyanins come from sugars that are produced in the leaves and trapped there; more intense sunlight leads to more rapid degradation of chlorophyll and the early appearance of intense orange and yellow hues from flavonoids in the leaves.
The contributors to the autumn festival of colors are many. Here are a few standouts:
The delicate flowers of the native witch-hazel, Hamamelis virginiana, are a discreet yellow but bloom so late there is little floral competition. Often, the yellow of the flowers overlaps with the bright yellow of this small tree’s falling leaves, so be sure to appreciate the blooms close up. They can be found scattered throughout Fern Valley.
In concert with yellow fall foliage, red berries as well as the orange and yellow ones of winterberry, Ilex verticillata, and its cultivars shine like bright jewels and often persist until late winter when they become a significant food source for cardinals.
And the berries of beautyberry plants, Callicarpa species, present a lovely and unexpected purple or white. Some can be found in the Asian collection, but hurry, since the tasty berries are devoured by birds almost as soon as they ripen.
Firethorn, Pyracantha ‘Teton’—This is a dense, columnar, evergreen plant with fine-textured dark green foliage. Its fruit begins to ripen in mid-October as a light yellow and later matures to a medium yellow orange which persists into January. There is one visible from the road by the Greenhouse.
ILEX ‘SUNNY FOSTER’
The leaves of this holly, Ilex ‘Sunny Foster’, that grow in the sun are bright yellow; leaves growing in shade are chartreuse. Its colorful red fruit is small but showy, about one-third of an inch wide. There are several large specimens in the Lavender Border at the east end of the Herb Garden.
The field of maple trees have brilliant color and include the red maple Arboretum Introduction Acer rubrum ‘Sun Valley’. Its brilliant red autumn color will warm your heart.
In Asia Valley, a number of trees remain beautiful after their leaves fall, especially the maple Acer henryi which has persistent seed pods that hang down from the tree in a grape-like effect.
Blue, the color of autumn blooming Aster ‘Raydon’s Favorite’, is also in abundance to the east of the Capitol Columns where it is intermixed with the golden autumn foliage of Amsonia hubrichtii. There, mixed with the earth tones of declining forbs and grasses, blue asters are the last bright note in the fading landscape.
-From the Fall 2017 Arbor Friends newsletter-
Captions: TOP: Yellow bloomsof native witch-hazel (Hamamelis virginiana). BOTTOM L-R: Purple beautyberry fruit of the genus Callicarpa. A glut of orange firethorn berries (Pyracantha ‘Teton’). Bright red fruit of a winterberry plant (Ilex verticillata). Yellow leaves of the holly Ilex × attenuata ‘Sunny Foster’. All photos courtesy of USNA.
Fall at the Arboretum has always been full of splendid plants and sights. This piece combines two articles from the Arbor Friends archives, including Carole Ottesen’s “Fall” piece in Fall 2012, and an unattributed “Arboretum Adventure: Finding Fabulous Color in Curator’s Collections” in the September-October 1995 issue. Arboretum staff reviewed this piece for accuracy in today’s collections.