Known in the nursery trade as the "queen of flowering trees," the Eastern flowering dogwood (Cornus florida) is one of spring's most beloved bloomers. Though several species look distinctly different from their famous white-flowered cousins, most species of dogwood tree and shrub feature conspicuous flowers. The entire genus is made up of between 20 and 30 species of medium-height shrubs or short trees, though only several of these are commercially available.
Tree Care and Culture
As forest understory trees, dogwoods generally prefer lightly shaded to partly sunny locations. Proper site selection can help prevent undue stress on the tree, which can lead to pest and disease issues. Though trees will grow well enough in full sun as long as there is adequate water, hot and sunny locations can invite attacks by the dogwood borer, a serious insect pest of the species. Dogwoods also prefer slightly acidic and moist yet well-drained soils.
Pests and Diseases
Dogwoods are not affected by many insect pests, but the dogwood borer is the exception. A clear winged, black-and-yellow moth, the borer also attacks oak and fruit trees. While infestations rarely kill the tree, repeated attacks or infestations that go untreated may wound a tree enough to cause cracking of the trunk wood and a gradual decline of the tree.
The main pathogen pests of dogwoods are anthracnose infections, caused by several types of fungus. Less serious infections manifest as black spots and cankers on the leaves and flower bracts of dogwood trees; these generally only cause discoloration and eventually holes in the foliage. Discula anthracnose is more dire, beginning as discoloration and black blighting of leaves and eventually causing twig dieback. Left untreated, the fungus will kill the tree as it progresses deeper into the vascular tissue. The University of Tennessee has been working for the past several decades on developing anthracnose-resistant cultivars such as Cornus florida, 'Appalachian Spring.'
Native Flowering Dogwood
Cornus florida, the flowering dogwood, is one of spring's most profuse bloomers. Many people mistake the four-petaled bright-white "flowers" that appear in spring; these petals are actually modified leaves that surround the true flowers in the center of the four-petaled configuration. Pink- and red-flowered varieties are also available. Trees rarely grow larger than 25 feet at maturity and make excellent small landscape trees or specimens for woodland settings.
Kousa dogwood (Cornus kousa) is also known as Chinese dogwood and differs from native dogwoods for two reasons. First, its four white bracts are pointed at the tips, where native dogwood flowers are rounded with a notch; and secondly, flowers appear after the tree has fully leafed out, where native dogwoods bloom before leaves unfurl. Kousa dogwoods can withstand sunnier sites than their native cousins but in all other regards are virtually interchangeable with native varieties.
Cultivars and Hybrids
The University of Tennessee and Rutgers University have been working on developing hybrids and cultivars of flowering and Chinese dogwoods for resistance to the tree's various pests and diseases. 'Appalachian Spring' was one of the first anthracnose-resistant varieties made commercially available, and UT is working on such varieties as 'Cherokee Brave,' 'Kay's Appalachian Mist' and 'Karen's Appalachian Blush' for resistance to powdery mildew.
Rutgers has been actively developing hybrids of native flowering and Chinese species to produce a line of trees called Stellar dogwoods. With names like 'Celestial,' 'Aurora' and 'Stardust,' hybrids have displayed increased resistance to both disease and insect pests.