This past Christmas season, some of my friends and family traveled to Pawleys Island, South Carolina, so that we could enjoy together the Nights of a Thousand Candles at Brookgreen Gardens, which was far more intriguing and magical than I ever imagined. However, my most memorable image is of the 100 or so flowering dogwoods that are regularly spaced on the long drive towards the Brookgreen Gardens Visitors’ Center. Growing in a semi-natural zone between the road and the actual woods, these native trees gave a display of both their fall and winter aspects. Some still had a nearly full array of leaves with variations of striking, predominantly red fall color. Others had lost their leaves, and their distinctive trunk and branching aspects were highlighted. Almost all retained some of their bright red fruits.
Cornus florida is the botanical name for South Carolina’s flowering dogwood, one of 16 dogwoods native to the United States. Its natural range extends way up in Eastern Canada and as far west in the United States as Texas. About 50 or so Cornus species are in the Northern Hemisphere. In this case, “florida” is a botanical word meaning flowering and is not connected with the state by the same name.
Speculation as to the origins of the common name “dogwood” in Great Britain is fun to explore. Some sources suggest that the bark was boiled to make a preparation to treat dogs with mange. In fact, decoctions of the bark were used as a substitute for quinine by Confederate troops during the Civil War. The wood, not valuable for traditional lumber building uses, does have an extraordinary resistance to shock, making it valuable for tool handles and such. A knife-like instrument with the old English name “dag” was commonly formed from the wood of an English species of this tree and became corrupted into “dogwood.” In the 1860s, commercial New England textile mills had a huge need for mature dogwood trees to be turned into spindles. The force that drove those looms required spindles with great shock resistance; dogwood also gets smoother with use, which made it perfect for that purpose.
For years, people planted dogwoods that were mostly propagated from locally collected seeds. Cuttings were taken for pink-flowered varieties, which do occur occasionally in nature. When I was studying horticulture, before several new deadly or troublesome diseases became common, we were taught that if we gave dogwoods certain requirements, they could flourish in most home landscapes. Many of those requirements still apply, with a few changes due to disease pressures. Unless you are in a particularly low or humid area with poor air flow, choose a site with morning sun and afternoon shade as dogwoods are naturally understory trees. Be sure the soil is slightly acidic, has very good drainage, and has a relatively high organic content. The central limbs grow horizontally and are somewhat widely spaced (unless planted in full sun), giving trees a graceful and open appearance. Make certain the site you choose won’t block a walkway as the tree grows.
Dogwoods are a four-seasons tree. The leaves have a beautiful fall color. The red fruits in winter are noticeable and attract birds that feast upon them. The open, branching structure and the blocky bark give winter interest. The University of South Carolina Curator Emeritus of the A.C. Moore Herbarium John Nelson’s favorite quip is, “How do you recognize a dogwood? By its bark.”
Yet, those glorious “flowers” are the main appeal. Spoiler alert: they aren’t really flowers but modified leaves called bracts. Four in number, mostly white, with a slightly darkened notch at the end, they surround the actual small center cluster of male and female flowers. From the female blossoms, deep red fruits called drupes develop. They are of immense importance to wildlife.
The plant guide of the United States Department of Agriculture’s Natural Resources Conservation Service, available online, informs us that these fruits are high in fat and calcium, and both songbirds as well as numerous mammals feast upon them. The leaves are also an important food for deer, rabbits, and beavers, and are a larval food source for the spring azure butterfly. In the Appalachian Mountains, dogwood drupes once provided more than 50 percent of the mast (fruits, berries, and nuts) consumed by animals.
Sadly, an introduced fungal disease, dogwood anthracnose (Discula destructiva) first diagnosed in New York forests in 1978, has since 1988 taken an immense toll on local mountain forests as well. Fortunately, the disease is mainly confined to areas above 2,000 feet. This disease usually kills infected trees within three to six years. One suggested replacement, Cornus kousa, or Korean dogwood, is resistant and is believed to be the source of this pathogen; however, its fruits are not edible by North American wildlife. The cultivar C. florida ‘Appalachian Spring’ is the only native dogwood with resistance to this disease. Individuals planning to plant dogwoods in an area where the disease is prevalent should make certain to obtain this cultivar.
The two other major new dogwood diseases are not limited to higher altitudes, so they are more of a consideration for the Midlands. Fortunately, although the diseases are disfiguring when they occur, they are seldom fatal. Spot anthracnose causes reddish brown lesions on bracts and leaves. It is most likely to happen when wet weather occurs right as the leaves and buds are developing in the spring. One year a bad infection may be evident, but then symptoms might not be seen the following year; the inoculum is always present but must have the right cultural conditions to cause infection. Dogwood powdery mildew has been more of a problem for me. This makes the leaves look as if they have been dusted with talcum powder. The mildew is likely to cause problems not in response to rain but when there are cool nights and warm days with high humidity.
Certain cultivars are resistant to one or another of these two non-fatal diseases (see Clemson HGIC Dogwood Diseases and Insect Pests for a listing), and you can help reduce the chances of your dogwood’s becoming infected by following certain cultural practices.
1) Although dogwoods prefer morning sun and afternoon shade, they also need good air circulation. Thin any dead or diseased branches and consider removing crowded plants. Overhead branches from nearby large trees may need to be thinned as well. Stressed plants are less resistant to infection.
2) Mulch is extremely important for dogwoods’ health as the trees have shallow roots and therefore need good soil moisture. Keep mulch 3 inches deep around your dogwood (not touching the trunk) extending at least halfway to the edge of the canopy. This also protects the bark of your dogwood from injury caused by lawnmowers or weed trimmer.
3) Don’t use overhead irrigation that wets the leaves and bark.
4) Use nitrogen fertilizers sparingly to avoid overly vigorous foliage that is more susceptible to diseases.
5) Fungicides can help control diseases but must be applied almost bi-weekly, and that frequency and the cost of a professional applicator to get adequate coverage limits that option to only very significant trees.
If you are adding new dogwoods to your landscape, visit a reputable local nursery and ask them for help in selecting cultivars with resistance to the most commonly reported problems they are seeing. Find the root flare and dig the planting hole only that deep or slightly higher; it is always better to plant a little high rather than lower, but do make the hole wider. Do not add amendments or fertilizer to the planting hole. Cut any circling or girdling roots. Many plants die years after planting because of people’s reluctance to adequately pull the roots apart at planting time. Mulch properly and irrigate with a slowly running hose whenever the soil is dry. In dry times during the first few years of a new dogwood’s life, this method will work better to keep the tree adequately moist than your irrigation system.
Although numerous disease-resistant cultivars are available that are crosses between our native dogwood and the Korean dogwood species, it is worth it to take time to find a true C. florida cultivar. The importance of its fruits to wildlife is more critical than ever with the current news from the National Audubon Society about the disappearance of North American birds. You will be rewarded when you see a beautiful cardinal or a noisy mockingbird perched in your dogwood enjoying the nutritious drupes, and you will know that it will be supporting birds, butterflies, and mammals long after you are gone.