Kousa dogwoods or Japanese flowering dogwoods (Cornus kousa) enrich the Roanoke Valley’s May and June landscape with crowns of star-shaped milky white “flowers.” Kousa dogwood trees are visible in residential, commercial and civic landscapes throughout the Roanoke Valley. According to the “Urban Forestry Plan,” an “Element of Vision 2001-2020” adopted on April 21, 2003 by the Roanoke City Council, there are 45 Kousa dogwood trees planted on city property that account for about 0.3 percent of city-maintained trees on streets and in parks. Further afield, Longwood Gardens, Kennnett Square, Pa has excellent middle-aged plantings near the Idea Garden, and older, mature specimens in the woodland near the Italian Water Garden.
Kousa dogwoods are deciduous trees which are about 20 to 30 feet high and an almost equal width when mature. Introduced to the American horticulture world in 1875, they originated in Japan, Korea and China. Mature trees in the Roanoke area blend as secondary, almost understory, trees with maple, holly trees and ornamental cherry trees. Although slow growers, they make excellent specimen trees with attractive winter structure in USDA Plant Hardiness Zones five through eight.
What appear as showy flower petals are really four pointed bracts – modified leaves – that surround compact clusters of small yellow-green flowers. These flower structures emerge in May shortly after leaves appear, peak in beauty during May and June, and gradually pink-up as they age and drop.
Watch the Kousa dogwoods during autumn and winter. Fall leaf colors are vivid reds, yellows, and purples. Pink-red to deep red globose fruits, between ½” to 1″ in diameter and resembling raspberries, appear in late August through October. They hang on trees long enough to resemble decorations on a Christmas tree. Our winter resident birds may dig seeds out of the fleshy fruit once it ages.
The bark on the upright Kousa tree is especially noticeable in winter with its attractive irregular patches of gray, brown, tan, and olive-green. Horizontally arranged slender stems stand out against snow, as do the flower and leaf buds. It is easy to tell the two apart since flower buds are longer and larger than the leaf buds.
The main advantage Kousa dogwoods have over their native American cousins, the flowering dogwoods, is resistance to various pests and diseases. Discula destructiva, the fungus that causes Discula or dogwood anthracnose, often kills flowering dogwoods two to three years after intial infection. This disease, introduced into the United States from unknown sources in the mid-1970s, infects, weakens and kills a great many native dogwoods in U. S. forests and landscape plantings.