Photo by Joey Williamson, Clemson Extension HGIC
Other trees may bloom earlier each spring, but none seems to stir up emotion and excitement like flowering dogwoods (Cornus florida). Their bright, white blooms, scattered throughout landscapes and forests, have widespread appeal in the South.
What most people think of as dogwood “petals” are actually modified leaves called bracts. The yellow-green clusters in the center of the bracts are the true flowers. Beyond flowers, these small shade trees offer brilliant fall color and sinuous branches in winter. They’re also prized for their fall-ripening berries, which benefit birds and other critters.
While this beloved tree is native to S.C. forests and does well in natural settings, dogwoods in the home landscape battle two devastating problems: drought and disease.
These deadly Ds are often exacerbated by manmade stresses. As understory trees, dogwoods are accustomed to moist, well-drained forest soils and high shade from mature oaks or pines.
Their shallow roots are sensitive to drought and flooding, making them poor competitors with turfgrasses in the home landscape. Around homes, soils tend to be compacted, low in organic matter and nutritionally poor—no friend to dogwoods.
October kicks off prime planting season for trees like dogwoods. You can help alleviate some stresses with proper site selection and good soil and water management.
Choose a planting site with partial shade, preferably afternoon shade. Dogwoods need well-drained, slightly acidic soil, rich with organic matter. Find an open, sparsely planted area where air circulates and foliage can dry quickly, to minimize foliar diseases. With adequate soil moisture, dogwoods can survive in full sun, but they’ll be more prone to drought-induced leaf scorch. Keep roots cool and moist with 2 to 3 inches of mulch, and don’t let grasses grow over the root zone. A healthy mulch ring also protects against two weapons of dogwood destruction, mowers and string trimmers, as bark damage leads to insect infestations. Insects, such as the dogwood borer, attack only stressed or injured trees.
As for diseases, the most troublesome are spot anthracnose and powdery mildew.
Spot anthracnose (not related to the more deadly dogwood anthracnose, uncommon in most of South Carolina) causes small, unsightly spots on flowers and leaves during years with wet springs. It generally doesn’t cause long-term harm, but two to three years of infection can weaken trees. Mostly, it’s a visual concern, as severe infections can curl and distort bracts, spoiling the spring show.
Powdery mildew is especially problematic and “may be the cause of the demise of many dogwoods in the deep South,” according to Dr. Alan Windham, a University of Tennessee expert on dogwood diseases. Powdery mildew infects leaves during periods of warm, dry days and cool, damp nights. As the name suggests, it appears on leaves as a white, powdery coating. Severe infections cause leaves to become distorted and have a purplish discoloration. Leaves may also develop dead spots, and trees may prematurely defoliate. When the disease strikes in late summer, damage is minimal, but if it hits in early summer, flower bud set can be reduced, decreasing blooms the following spring.
Humidity is the enemy here—powdery mildew is worse in dense, shady areas with poor air circulation. Clear areas around existing dogwoods, and limb up overhanging branches from surrounding trees to improve air circulation and increase sunlight penetration. Rake up all fallen leaves, and prune off dead or infected stems. Severe disease may warrant fungicide treatments, but, to be effective, fungicides such as myclobutanil and propicanzole must be applied as soon as symptoms appear.
For new plantings, your best defense is to buy resistant varieties. Windham recommends the Appalachian series, developed by UT for disease resistance, which includes Appalachian Spring, Appalachian Blush, Appalachian Mist and Appalachian Joy (named for his wife, Joy). If you prefer a pink-flowering dogwood, try Cherokee Brave.
Nonnative Kousa dogwoods (Cornus kousa) are generally resistant to these problems, but their shape and later bloom time just don’t speak to my Southern soul the way a healthy flowering dogwood does.
S. Cory Tanner is an area horticulture agent for Clemson Extension based in Greenville County. Email him here.