Dogwoods for North Carolina
North Carolina State University
Introduction: Dogwoods, i.e., plants within the genus Cornus, include shrubs and trees that have great potential value in NC landscapes. While some may be seen as multi-season interest plants, they have one season of greatest landscape impact, either winter or spring.
The wintertwig dogwoods are grown primarily for their colorful stems but some also have attractive foliage and, during their brief flowering period, may attract butterflies. They should be planted in moist, sunny sites.
Both Cornus alba, the Tartarian dogwood, and Cornus sericea, Redosier dogwood, are native and called wintertwig dogwoods. Both species can achieve heights of 8 to 10 feet and can be at least as wide. The best stem color develops on young stems growing in sunny locations. Therefore, pruning plants to near the ground in late spring at least every three years will keep plants shorter as well as increasing their color display significantly.
In the mountains, most cultivars will perform well. However, in USDA Hardiness zones 7 and 8 the Cornus sericea cultivars perform best. In the piedmont and coastal plain, Cornus sericea 'Cardinal' stem color is more yellow to orange rather than the cherry red seen in the mountains. 'Bloodgood,' a C. alba, shows deep red stems in the Piedmont and Mountains but is less vigorous than 'Cardinal' or the C. sanguinea cultivar 'Midwinter Fire' which displays a similar combination of red/yellow/orange stems. Cornus sericea 'Silver and Gold' has yellow winter stems and creamy yellow variegated leaves. It has performed well in the mountains and piedmont.
Cornus mas, Corneliancherry dogwood, is often a multistemmed small tree which is grown for long lasting yellow flowers that appear from mid-February into March, before forsythia, at a time when little else is flowering. They should be planted in average soil in full sun or light shade.
Most cultivars flower well in the mountains with 'Golden Glory' being one of the most popular. However, Cornus mas flowering was limited in the piedmont and coastal plain until the introduction of the cultivar 'Spring Glow' by the JC Raulston Arboretum. 'Spring Glow' has performed well and flowered freely in state-wide test locations as diverse as Wilmington and Boone.
The bright red fruit of Corneliancherry dogwood are edible. Cultivars exist with large cherry-red, yellow, purplish or white fruit . . . all of which are used to make preserves and syrups. Isolated individual trees rarely set fruit. Cornus officinalis, a species with similar habit and flowers, is rarely seen in NC but has promise for a similar late winter floral display.
Easily the most popular cultivated dogwood is Cornus florida, the native flowering dogwood. The value to just the Tennessee nursery industry is estimated as $30 million annually. Cultivar selections have been made for red and pink bracts, variegated and purple foliage, double flowering (multiple bracts), disease resistance, yellow rather than red fruit, yellow twigs, compactness, flower size and numerous other characteristics during the over two centuries flowering dogwood has been in U.S. nurseries.
Flowering dogwood is usually a forest under story or edge tree that rarely exceeds 25 ft. in height. In the coastal plain and much of the piedmont it performs best in light shade or morning sunshine with afternoon shade. In the mountains, morning or all day sunshine is best to avoid disease problems. In addition, flowering dogwoods are shallow rooted and perform better with a few inches of organic mulch over the roots rather than grass or other highly competitive plants. Irrigation during droughts, liming every three years to a pH of around 6.0, and a light annual application of fertilizer are all beneficial for flowering dogwood health in much of North Carolina.
Where disease is not a major problem, 'Cherokee Princess' for white bracts and 'Cherokee Chief' for red bracts have consistently been top performers in North Carolina. Where powdery mildew (Microsphaera pulchra) is a problem, red bracted 'Cherokee Brave' has been the standard with new 'Kay's Appalachian Mist,' 'Karen's Appalachian Blush' and 'Jean's Appalachian Snow' cultivars from the University of Tennessee showing excellent mildew resistance. These TN cultivars may not be available for a couple of years.
Dogwood anthracnose, caused by the fungus Discula destructiva, is a major problem in the mountains and areas with prolonged cool, moist weather but not in the coastal plain and much of the piedmont where weather is regularly warmer. Plant flowering dogwoods in the full sun and provide good cultural conditions in the mountains to help avoid this disease. As the cultivar 'Appalachian Spring' becomes available from the University of Tennessee introduction program, a flowering dogwood cultivar with dogwood anthracnose resistance will be available.
While numerous pests exist (http://dogwood.ag.utk.edu/) few are fatal. Most pests can be limited in severity by proper siting, planting and cultural practices. Flowering dogwood remains one of the most popular small flowering trees in North Carolina landscapes and woodlands.
Swamp or silky dogwood, Cornus amomum, is a native species important to North Carolina. It does not have large bracts. Instead the flowers are borne in white, flat topped cymes which are followed by clusters of abundant bluish fruit which turn black in late summer. Cornus amomum is an important wetlands stabilization species across the Eastern United States while proving bird forage in late summer.
Cornus kousa, the oriental dogwood, can be a highly ornamental small tree with bright white or pink bracted flowers contrasted against dark green foliage in late spring. Unlike flowering dogwood which is in full bloom before or as foliage unfolds in spring, oriental dogwoods flower after leaves are fully expanded. Fruit somewhat resemble a red raspberry in color and form but are borne on a stem like a cherry. They are edible as opposed to tasting good.
Oriental dogwood thrives in sunny, average soil sites in the mountains and in cooler parts of the North Carolina piedmont. Most cultivars are not reliably heat tolerant. A much deserved popularity increase occurred in the 1990's because the species was alleged to display overall good resistance to dogwood anthracnose. Superior cultivars are just reaching the marketplace. White bracts: 'Blue Shadow,' 'Greensleeves,' and 'Milky Way Select'; Pink bracts: 'Satomi'/'Rosabella' Variegated foliage: 'Gold Star' and 'Wolf Eyes.'
An "evergreen" oriental dogwood is sold variously as C. kousa var. angustata or C. angustata. It is not evergreen during a normal mountain winter. By midwinter in areas where foliage remains on the tree, leaves are a purplish silvery green. This plant has narrower leaves and flower bracts than oriental dogwoods previously mentioned but also superior heat tolerance and otherwise the general characteristics of the species.
The Stellar series of flowering dogwood trees arose from hybridization done by Dr. Elwin Orton at Rutgers University. All are trademarked. Parents of these hybrids are flowering dogwood and oriental dogwood. Most of these hybrids display more vigor and grow to tree form earlier than either of their parents. All cultivars display adequate resistance to dogwood anthracnose if grown in full sun. Five cultivars, Ruth Ellen, Stardust, Constellation, Celestial and Aurora flower white. For good resistance to both mildew and anthracnose, choose Celestial and Stellar Pink. Stellar Pink flowers a pleasant pale pink in the mountains during a cool spring but pigment development is very light in the warmth of most piedmont spring seasons.
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