Dogwood

#TeachingTuesday: Dogwood

Today we will be covering the flowering dogwood (Cornus florida). There are also Chinese dogwoods (Cornus kousa) and many other types of dogwood trees and shrubs, but we are only talking about the common one native to the eastern United States. If you go hiking in the woods in North Carolina in March or April, chances are you will come across a dogwood tree in flower. Dogwoods are small understory trees that grow in hardwood forests, often growing alongside maples, oaks, and redbud trees. Dogwoods are fairly unremarkable most of the year, but quite stunning in full bloom—the large flowers draw much attention in the early- to mid-spring, when most trees are still barely leafing out. Most dogwoods in nature have white or cream flowers, but there are several pink varieties available in the nursery trade, most of which derived from a naturally pink subspecies, Cornus florida rubra. The Cherokee and Appalachian lines of dogwoods have been bred for excellent disease resistance and attractive flowers.

Dogwoods bloom on old wood, setting the flowers for the following year during the summer.  They rarely need pruning, except to remove crossing or rubbing branches, water sprouts, or dead/dying branches. They will bloom more in sunny locations, but too much harsh sunlight can damage the leaves and stress the tree.

The biggest problem for dogwoods is a fungal disease called dogwood anthracnose, which can cause branch dieback and even kill entire trees. It is spread by water droplets carrying the pathogen. If you have an infected tree, you will start to see symptoms in mid- to late-May, when leaf spots will appear, and cause irregular-shaped holes in the leaves with purple or tan borders. You may also see tan spots on the flowers. This disease is common in nature, so you should never try to transplant a dogwood tree from the wild into your yard. Luckily, plant breeders have developed cultivars that are resistant to dogwood anthracnose, as well as several other problems like powdery mildew, that dogwoods often have. C. ‘Appalachian Spring’ was the first cultivar that was developed, but today there are several. There are also hybrids developed from crosses with Chinese dogwoods which are naturally resistant.

ID Tips

• All Dogwood leaves have a distinctive pattern of veins that arc toward the tip of the leaf. If you very gently tear the leaf in half across the veins, you will see white spiderweb-like threads. However, since all species of dogwood have similar veins, this will not help distinguish between different species.
• The floral buds are the key identifier of a dogwood in winter when no flowers or berries are present. At the end of each branch tip will be an onion-dome shaped bud about the size of a pea.
• The flowers (technically inflorescences) have 4 large bracts (petal-like structures), which may be white, cream, or pink, with purplish or tan tips that are slightly curled, as if they had been burned and shrank up. There is a small cluster of tiny yellow flowers in the center of the inflorescence.
• The tiny yellow flowers in the center will develop into clusters of bright red, shiny berries through summer and fall. The berries are not round, but slightly elongated, like a Roma tomato.