Dogwoods — Spring in Virginia
Spring in Virginia is the season of the dogwood, with flowering dogwood, Cornus florida, serving as both the official state tree and the state flower. Bloom season is long and beautiful, starting with the Cornelian cherry dogwood (Cornus mas) in March, flowering dogwood (C. florida) in April, the kousa dogwood (C. kousa) in May, and the pagoda dogwood (C. alternifolia) in May to June. In addition to spring blooms, each species offers colorful berries in the fall, autumn leaf color, and interesting bark in winter. Of these four species, the flowering dogwood (C. florida) and pagoda dogwood (C. alternifolia) are native to North America, in particular, to the eastern U.S. This article will discuss all four species of dogwoods, highlighting similarities, differences, and suitability to different sites.
BRACTS AND FLOWERS
Cornus is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods. Each species brings its own value to the landscape. The “flowers” of the flowering dogwood and kousa dogwood are not actually flowers but bracts, which are modified leaves that look like petals. The true flowers are clustered in the center of these bracts. The “flowers” may be white, pink or yellow. Pagoda dogwood lacks the showy bracts of the flowering dogwood, but has 2″ flat clusters of fragrant, white flowers appearing in May to the beginning of June. The small yellow flowers of the Cornelian cherry appear very early in spring, sometimes before forsythia, and often remain long into spring. Flowers are borne in tiny clusters close to the naked stems.
Both the flowering and Cornelian cherry dogwoods flower before the leaves appear. The kousa dogwood and pagoda dogwood flower after the leaves appear.
One of the most appealing features of many dogwoods is the graceful beauty of their tiered, horizontal branching, especially true of the flowering dogwood and the kousa dogwood when they are sited in shade. Cornelian cherry tends to be multi-stemmed and is formed more like a shrub than a tree.
FRUIT, FALL FOLIAGE, AND BARK
Cornus florida Photo: Ram Man, Creative Commons
Flowering dogwood: Maturing in late summer to early fall, the bright red fruits are loved by birds and wildlife. Fall leaf color is red to reddish-purple, although trees sited in full shade may have poor fall color. The dark, reddish-brown bark is rough and deeply checkered, making it an effective marker for tree identification.
Pagoda dogwood: Black-blue droops appear in July and August. The fruit stalks remain and turn an attractive red. In fall, the foliage becomes a mix of yellow and maroon. The bark is smooth, dark green, and streaky; eventually turning light brown with narrow fissures.
Kousa dogwood: Showy, pinkish-red to red fruits resembling raspberries appear in September and October. The fruits are edible, although somewhat mealy. Fall leaf color varies from purple to red to yellow. As kousa dogwood matures, the lower bark peels and creates a unique pattern similar to sycamore tree bark.
Cornelian cherry dogwood: Medium to large-sized fruits mature to cherry red in mid-summer. Although sour tasting fresh off the plant, fruits are edible and often abundant and may be used for making syrups, preserves, and pies. Fall leaf color is often poor, ranging from dull green to purplish red. The bark is dark gray to reddish brown and becomes scaly and exfoliating as the tree matures.
PLANTING AND CARE
Dogwoods prefer moist, well-drained, acidic (5.5 to 6.0 pH) soil that is high in organic matter. The flowering dogwood and pagoda dogwood prefer partial shade, especially shade in the hot afternoon. Both the kousa and the Cornelian cherry do well in full sun or partial shade, and are more sun tolerant than the flowering or the pagoda dogwoods. Dogwoods have shallow roots, and none of the dogwoods tolerate drought. Even established trees will benefit from watering during hot, dry spells. If irrigation water is applied by sprinklers, it should always be done in the morning to reduce risk of foliar disease. Good air circulation is necessary to hasten drying of leaves after rainfall and to lower the risk of disease.
FERTILIZING
Fertilize dogwoods lightly in the spring once frost has passed with a well-balanced (2-1-1), extended-release, acid-forming, azalea fertilizer. Fertilize again six weeks later to encourage extra flowers or faster growth of young trees. Avoid using high-nitrogen lawn fertilizers around dogwoods. Excessive nitrogen can cause the tree to develop more leaves at the expense of flowers. Avoid fertilizing trees stressed by drought during the summer months.
PRUNING
All these species form their buds on old wood; if you prune dogwoods either in the fall or in the early spring before they bloom, you’ll remove the flower buds. Most dogwoods will not need pruning, but if you must prune, do so immediately after the tree flowers in the spring. This will allow the tree time to produce new growth and flower buds for the following year.
DISEASE
Flowering dogwood is susceptible to numerous diseases and pests, including powdery mildew (Erysiphe pulchra), dogwood anthracnose, (Discula destructiva), and spot anthracnose (Elsinoe corni). Of the four species, the flowering dogwood is the most susceptible to anthracnose and powdery mildew; the kousa dogwood is more resistant; and the pagoda dogwood and the Cornelian cherry are considered to be a generally pest-free plants with good resistance to powdery mildew and dogwood anthracnose.
FLOWERING DOGWOOD (C. FLORIDA)
Cornus florida Photo: Line1, Wikimedia Commons
The flowering dogwood is the species most people think of when the word dogwood is mentioned. This is a lovely, small, flowering tree with short trunk and crown of spreading or nearly horizontal branches. During the Civil War, dogwood bark was used as a substitute for quinine. Native Americans used the aromatic bark and roots as a remedy for malaria and extracted a red dye from the bark and roots.
CHARACTERISTICS
The flowering dogwood will grow 40′ tall when grown as an understory tree in a woodland setting. In the sun, the same tree may only grow 15-20′ tall and wide. Spread can be greater than height at maturity. It can be grown as a single- or multi-trunk tree. A slow to moderate grower, it can grow 15′ in 18 years. It prefers rich, well-drained, acid soil.
POWDERY MILDEW
Powdery mildew usually occurs late in the summer and is of little consequence. Infection that begins early in the season, however, can be devastating, and the use of fungicides may be warranted.
ANTHRACNOSE
Flowering dogwood is seriously threatened by dogwood anthracnose which is caused by a fungus. Although a serious disease, there is some evidence that it is less widespread than before. The disease first became a problem around 1980 and spread rapidly throughout the trees’ range. Symptoms of anthracnose include large tan blotches or purple-rimmed leaf spots. Infected leaves tend to remain on the tree after they normally would have fallen. Trees are typically killed in 2-3 years. The fungus requires high humidity for infection, so trees growing in moist, shady sites are most susceptible. Hearty, well-maintained flowering dogwood trees in sunny areas with good air circulation and proper soil moisture are rarely impacted by anthracnose. High applications of nitrogen fertilizer can promote succulent new shoots which are more susceptible to the fungus.
C. florida ‘Appalachian Spring’ was found growing wild at the Camp David Presidential Retreat on Catoctin Mountain in Maryland where it exhibited strong resistance to anthracnose. It was developed by the University of Tennessee’s Dogwood Breeding program,
PESTS
Flowering dogwood is susceptible to the dogwood borer (Synanthedon scitula), a clearwing moth that is attracted to weakened trees, pruning cuts, and sunscald-damaged bark areas. Other commonly-occurring insect pests include the dogwood clubgall midge (which causes club-shaped galls or swellings on twigs), granulate ambrosia beetle, scale insects, and leaf miner. Unless the tree is under stress from other factors, insect damage is usually not severe.
For an excellent discussion of flowering dogwood pests and diseases, and a list of cultivars that are more resistant to these problems, refer to “Dogwood,” Clemson Home & Garden Information Center (HGIC) and “Dogwood Diseases and Insect Pests,” Clemson HGIC.
OTHER PROBLEMS
Leaf scorch may occur when conditions are too dry. Leaves have dry and browning edges and leaf drop may also occur. Although leaf scorch may look like a disease, it isn’t. Dogwoods respond positively to consistent moisture. Just as they suffer in drought, they also do poorly when planted in sites with poor drainage or in areas subject to flooding. When soil becomes too wet, dogwoods are prone to root rot (Phytophthora species).
WILDLIFE VALUE
Cornus florida fruit Photo: KENMEI, Wikimedia Commons
Flowering dogwood is a valuable food plant for wildlife because high calcium and fat contents make it palatable. The fruits are eaten by migrating birds and are an important food for overwintering birds such as bluebirds. Fruit is also eaten by ruffed grouse, quail, black bear, deer, chipmunks, skunks and squirrels. The fruits, flowers, twigs, bark and leaves are eaten by a variety of wildlife.
The flowering dogwood is a larval host for the spring azure butterfly (Celastrina ladon). The tree is also recognized by pollination ecologists as attracting large numbers of native bees. It also attracts predatory or parasitoid insects that prey upon pest insects.
FRUIT
Although different sources make different claims regarding the toxicity of flowering dogwood berries, according to the USDA, the berries are poisonous to humans.
PAGODA DOGWOOD (C. ALTERNIFOLIA)
Cornus alternifolia Photo: Ser Amantio de Nicolao, Plant Image Library, Boston, Wikimedia Commons
Pagoda dogwood is a also commonly known as alternate-leaf dogwood. Unlike most other native dogwoods, this species has alternate rather than opposite leaves. The name Pagoda Dogwood alludes to the flat-topped crown, with horizontal layers of branches. Branches are nearly parallel to the ground, giving the plant an attractive tiered effect.
CHARACTERISTICS
Cornus alternifolia flower Photo: US Environmental Protection Agency, Wikimedia Commons
This is a low-branched tree or large shrub reaching 15-25′ feet high and wide. Pagoda dogwood has greenish to reddish, or purple to purple-brown stems. The leaves form an umbrella-like shade because they are clustered near the ends of twigs. Pagoda dogwood prefers acidic, well-drained, consistently moist soil but it is tolerant of poor soils and clay. It will tolerate only short periods of drought. It is important to keep the root zone cool and moist. Pagoda dogwood does best in shade to part shade. In warmer climates, it is best planted on the north or east sides of buildings so that it is in direct sunlight for only part of the day.
Pagoda dogwood performs best in colder climates. It is hardy in Zones 3 to 7. In VA, it is frequent in the mountains and infrequent to rare elsewhere.
WILDLIFE VALUE
Cornus alternifolia fruit Photo: Steven Katovich, USDA Forest Service, Wikimedia Commons
Its bitter berries are consumed in fall and winter by wildlife including grouse, pheasants, wild turkeys and squirrels. Birds and butterflies are also attracted to the tree. It is a larval host for the spring azure butterfly, Celastrina ladon.
PROBLEMS
Although pagoda dogwood is susceptible to twig blight, leaf spot, and canker, it is infrequently affected by insects and disease. Wind and ice damage are common; a planting site protected from wind is preferable.
KOUSA DOGWOOD (C. KOUSA)
Cornus kousa Photo: Ser Amantio di Nicolao, Plant Image Library, Boston, Wikimedia Commons
Native to Japan, Korea and China, the first scientific observations of the kousa dogwood in the United States were recorded in 1875. Other names for this species include Chinese dogwood, Japanese dogwood, Japanese flowering dogwood, and Japanese strawberry tree.
CHARACTERISTICS
Cornus kousa Photo: DanGong, Wikimedia Commons
Cornus kousa berries Photo: David Stang, Wikimedia Commons
The kousa dogwood will grow 15-30 feet tall and wide. A slow to moderate grower, it will grow about 10 feet in 15 years. Younger trees grow upright, but with age, they spread more broadly with horizontal branching. Falling fruits may create a litter problem and should be considered in site selection.
KOUSA CULTIVARS AND HYBRIDS
Kousa dogwoods and their hybrids are generally more resistant than native dogwood to dogwood anthracnose, spot anthracnose, powdery mildew, and common dogwood borers. The Stellar series of cultivars, developed by hybridizer Elwin Orton of Rutgers University, are hybrids between the flowering dogwood and the kousa dogwood. They are generally free of diseases but may not be desired by gardeners wanting the pure form of the native tree. The hybrids produce showy bracts and have exhibited resistance to anthracnose in ongoing field tests. Their trademarked names are Ruth Ellen, Constellation, Aurora, Galaxy, Stardust, and Stellar Pink.
The variety Ruth Ellen is said to have the closest look of the native species, but generally the other Stellar introductions are midway between the two species in their habit, flower shape, and blooming period. They are sterile and don’t produce decorative berries, but are particularly showy in bloom.
See C. kousa, NC State Extension for a sample list of kousa cultivars.
A CAUTIONARY TALE
According to NC State Extension, kousa dogwood provide fruits and nesting sites that are attractive to songbirds. Squirrels eat the fruits as well. However, according to an article by the National Wildlife Federation, kousa berries are “monkey food,” which makes them valuable in Asia but not in North America. “Nothing eats them here,” says Doug Tallamy, a professor of entomology and wildlife ecology at the University of Delaware. “They’re not part of the food web.”
This article also identifies C. kousa as being the original source of bringing dogwood anthracnose into North America.
Sometime after kousa was first introduced to the United States by novelty-seeking nurseries in the 19th century, it likely unleashed the disease on defenseless native trees that had not evolved with the fungus. As Americans watched their flowering dogwoods die starting in the 1970s, landscapers encouraged them to replace the trees—with more kousas. “I don’t know a general in the U.S. military who could come up with a better invasion strategy,” says Kevin Heatley, an Ohio-based restoration ecologist.
Doug Tallamy, on p. 74 of Bringing Nature Home, identifies C. kousa as the likely carrier of dogwood anthracnose into the U.S.
CORNELIAN CHERRY DOGWOOD (C. MAS)
Cornus mas Photo: Wilhelm Zimmerling, Wikimedia Commons
The Cornelian cherry dogwood is native to southern Europe and western Asia and has been cultivated since ancient times for the fruit, which is excellent for preserves and syrup. On March 31, 1774, Thomas Jefferson recorded in his garden diary planting four “Ciriege Corniole” or Cornelian cherry trees along with sixteen other varieties of fruit trees and vegetables.
CHARACTERISTICS
Cornus mas flower Photo: AnRo0002, Wikimedia Commons
Cornelian cherry is a rounded, multi-stemmed small tree or large shrub with a network of fine stems. It matures to 20-25’ tall and 15-20’ wide. It responds well to pruning and may be pruned to produce a more upright habit. A slow to moderate grower, it will grow 20 feet in 25 years. It thrives in well-drained urban conditions as a specimen plant, in masses, or as a hedge.
FRUIT
Cornus mas fruit Photo: Wouter Hagens, Wikimedia Commons
The fruit is medium to large, maroon-red, cherry-like, edible, and attractive to birds. Two different varieties of Cornelian cherry trees are needed to get fruit. Cornelian cherries should bear fruit in 2-5 years, with full fruiting in 5-8 years. Harvest fruit in late summer; fruit can be astringent if harvested too early. Falling fruit may create litter problems and can temporarily stain walks and concrete.
The cultivar ‘Spring Glow’ may be the best selection for warmer southern climates. The cultivar is known for its good foliage and brighter yellow blooms than the species.
SUMMARY
Dogwoods are considered one of the most beautiful flowering trees in Virginia, and a true harbinger of spring. The native selection, flowering dogwood, has been plagued by dogwood anthracnose, a fungal disease which thrives in the same kind of site conditions favored by the native tree: shade and moisture. If planted in sunnier spots, care must be taken to provide ample watering. The native pagoda dogwood is resistant to anthracnose. Like the flowering dogwood, it prefers shade, needs ample moisture, supports native butterflies and insects, and is a valuable food source for wildlife and birds. It grows in USDA hardiness zones 3-7, placing Virginia in its most southern zone. The Kousa dogwood, an Asian species, is far less susceptible to dogwood anthracnose but the species is not a comparable food source for native insects and wildlife. There are many beautiful and disease-resistant hybrids of flowering dogwood and kousa dogwood, but be mindful that these hybrids are sterile and don’t produce fruit. The Cornelian cherry dogwood is more shrublike, blooms in very early spring, has abundant, small, yellow flowers, and edible fruit. It is also resistant to dogwood anthracnose. Each of these dogwoods offers beauty in the landscape. You need to weigh the pros and cons and decide which best suits your planting site, and your vision of spring!
SOURCES
Bringing Nature Home (Douglas W. Tallamy, 2009)
“Dogwood,” Clemson Home & Garden Information Center, https://hgic.clemson.edu/factsheet/dogwood/
“Dogwood Diseases & Insect Pests,” Clemson Home & Garden Information Center, https://hgic.clemson.edu/factsheet/dogwood-diseases-insect-pests/
Flowering Dogwood, USDA Plants, https://plants.usda.gov/plantguide/pdf/pg_cofl2.pdf
“Dogwood Anthracnose (Discula) – Trees,” University of Maryland Extension, https://extension.umd.edu/hgic/topics/dogwood-anthracnose-discula-trees
“Flowering Dogwood,” University of Kentucky, https://www.uky.edu/hort/Flowering-Dogwood
“Tried and True Native Plants of the Mid-Atlantic, Cornus Alternifolia,” Master Gardeners of Northern Virginia, https://mgnv.org/plants/trees/pagoda/
Pagoda Dogwood, University of Kentucky, https://www.uky.edu/hort/Pagoda-Dogwood
Cornus alternifolia, Lady Bird Johnson Wildflower Center, https://www.wildflower.org/plants/result.php?id_plant=coal2
Cornus Alternifolia, Cornell University Woody Plant Database, http://woodyplants.cals.cornell.edu/plant/62
Kousa Dogwood, Cornus kousa, Virginia Cooperative Extension, Hort 16NP, https://www.pubs.ext.vt.edu/HORT/HORT-16/HORT-16.html
Cornus kousa, NC State Extension, https://plants.ces.ncsu.edu/plants/cornus-kousa/
“Going Native,” The National Wildlife Federation, https://www.nwf.org/Magazines/National-Wildlife/2017/April-May/Gardening/Going-Native
Cornelian Cherry Dogwood, Morton Arboretum, https://www.mortonarb.org/trees-plants/tree-plant-descriptions/cornelian-cherry-dogwood
Cornelian Cherry, Thomas Jefferson’s Monticello, https://www.monticello.org/house-gardens/in-bloom-at-monticello/cornelian-cherry/
Cornelian Cherry Dogwood, Cornus mas, Bernheim Arboretum and Research Forest, https://bernheim.org/learn/trees-plants/bernheim-select-urban-trees/cornelian-cherry-dogwood/
Feature Photo: Cornus florida, Katja Schulz, Wikimedia Commons