The Japanese cornel dogwood is not as common as its twin, C. mas, corneliancherry dogwood, and arguably difficult to separate. C. mas is well established in the nursery trade and, since phenotypically similar, why grow and support a like-minded relative. In this horticultural court room allow me to present my case for consideration before the American nursery jury rules on its worth.
My first exposure to the true species occurred at Bernheim Arboretum in Clermont, Kentucky, and the Arnold Arboretum in Jamaica Plain, Massachusetts. Those trees held firm to the botanical and horticultural features, including earlier flowering, later fruit maturation and a somewhat mosaic-patterned exfoliating bark of gray, orange and brown. I have recorded flowering as much as 10 to 14 days earlier than C. mas. Tufts of brown pubescence are present in the vein axils on the lower surface and there are typically more veins per leaf – five to seven compared to three to five for C. mas. As in all biological organisms, the shades of gray muddle/mute/distort the absoluteness.
The species is native to China, Korea, and Japan where it grows in forests, forest margins, and mountain slopes at elevations from 1,300 to 7,000 feet. It develops into a small tree or large shrub in the 15-25 feet range, as wide as tall, with rather fine-textured, slender stems. The largest specimen in the southeast I’ve observed was 20-by-20 feet at the former Specialty Ornamentals in Watkinsville, Georgia. The Secrest Arboretum in Wooster, Ohio, listed a 22-by-35-foot, 45-year-old specimen.
Foliage is dark green in summer and a few degrees of bronze-red in autumn, but it’s primarily green until the first freeze in the Athens area. I can’t remember a vibrant fall-colored tree, although the English literature mentions “rich autumn tints” and the former Klehm’s Song Sparrow Nursery once offered several clones with red to red-purple fall color.
The flowers, glorious sulfur-yellow to mustard yellow, in ¾-inch wide stalked umbels, develop on the naked branches when most needed to cure the winter blahs. Flowering occurs in mid-February in Athens with statistical 10 to 14 days on either side of “mid” and a month later in Boston. Flowers are effective for many weeks and even as petals fall, the light cream-yellow sepals continue to persist.
The species appears to be self-fertile because isolated trees form fruit, but I’m not sure whether insects are involved in pollination. The red to purplish red, narrow-ellipsoidal fruits (½ to ¾ inches long, up to 1/3 inches wide) ripen in September-October. Fruits are astringent (apparently not relished by birds) and I observed them persisting (still colorful) in quantity in February as flowers were opening. In China, the fruit is called “zhu zu” or “zao pi” where it is utilized in medicines.
The species appears impartial about cultural conditions as well-drained soil, acid to slightly basic, and full sun to partial shade are all acceptable. A 94-year-old specimen at the Arnold is testimony to longevity. It is adaptable from Zone 5 to 8.
Mark Griffith and I have evaluated numerous seedlings with the hope of finding something unique. Seeds germinated readily with three months warm and three months cold treatment. Nothing to show for our efforts! Cuttings in my experience are difficult to root, although there are several cultivars that are produced this way.
I first observed ‘Kintoki’ at Wisley Garden in England. It’s a superior flowering form with slightly larger and more abundant flowers. Flowers opened in early February in the Dirr garden. Growth habit is shrub-like. It is available in U.S. commerce.
In 2017 I purchased Red Sentinel (‘KLMQQ’) and Rugged Charm (‘KLMII’) from the former Klehm’s. The foliage is sheeny, shimmering, glistening dark green on both with reported red fall color. Indeed, the summer foliage was beautiful but fall color in 2017 did not materialize as the foliage was rendered tatty by the Georgia heat.
A German cultivar, ‘Robins Pride’, surfaced on YouTube; young plants with extraordinary quantities of large yellow flowers. Other cultivars include ‘Sunsphere’ with earlier flowers from Tennessee; ‘Lemon Zest’ (‘Morris Arboretum’) with superior flower size and color was derived from open-pollinated seed of accession #1936-5430*A; and ‘Issai Minari’, which flowers heavily as a young plant.
I believe there is something in the water as Kim Shearer, a breeder at Morton Arboretum, mentioned in correspondence (accompanied with photos), a selection with excellent red fall color and readiness to root from cuttings. It was derived from open-pollinated seed planted by former breeder, Sue Wiegrefe. The selection is in production trials and has been distributed to a few nurseries. Sounds hopeful and obviously there are others who believe the species has merit.
For more than 40 years, horticulturist, breeder, and author Michael A. Dirr has impacted the green industry through research, teaching, books, and plant introductions. firstname.lastname@example.org