Cobb County Cooperative Extension
Plant of the Month
By: Emily Harper
There is no doubt the beautiful flowering dogwood is a southern favorite. Two species commonly used in the South are
Cornus florida, a Georgia native found flourishing in the forest understory and the Cornus kousa a native from China. From white to varying shades of pink and red, Dogwood blooms are a welcome sight in early spring.
PLANT SELECTION
If you are thinking of adding this traditional plant to your landscape there are a few points to consider. Do not transplant one from the woods. Introducing a tree from the wild may invite disease into your neighborhood. Wild Dogwoods are not prolific bloomers and can not compete with the blooms of cultivates varieties. Nurseries and garden centers carry both the Cornus florida and the Cornus kousa.
When selecting a plant, choose a healthy plant. Select a plant with a good shape and form. Container grown plants should have a healthy, white root system. Roots should not be ‘crowded’ in the pot.
CORNUS ‘florida’
WHITE BRACTS PINK/RED BRACTS
Barton American Beauty Red
Cherokee Daybreak Cherokee Chief
Cherokee Princess Cherokee Sunset
Cloud 9 Junior Miss
Bay Beauty Stokes Pink
Weaver’s White
The Cornus kousa has superior pest and disease resistance. It is a good choice if you have more sun than shade. It develops a bit slower than the Cornus florida, but will reach heights of 20 feet or more.
CORNUS kousa
WHITE BRACTS PINK/RED BRACTS
Ruth Ellen Stellar Pink
Stardust
Celestial
Milky Way
ENVIRONMENT
Dogwoods grow best as an ‘understory’ plant and perform well when planted in association with larger trees providing an environment of moderate shade. Heavy shade is listed as one of the primary obstacles to growth and health. A ratio of 60% full sun is considered appropriate. Dogwoods are adaptable to various soils, but grow well in soils that are medium to high in organic matter. Moist, non-compacted soil is preferred. A layer of organic matter on the soil surface is recommended. Good drainage is essential to aid in disease prevention. Dogwoods grow at a slow to moderate rate to about 20 feet in 25 years. They have a life span of 20-30 years although older and larger specimens exist.
PLANTING
When planting, it is appropriate to dig a saucer shaped hole at least 2 times the size of the root ball or container. The top of the root ball should be level or just slightly higher than the soil surface. When filling with the removed soil, eliminate rock that may be present. Cover the area with mulch such as pine bark nuggets, pine straw or other organic matter. Top dressing should extend to 50% beyond the size of the tree canopy. Avoid piling mulch on trunk by leaving a clear area of 3-4 inches.
WATERING
Dogwoods are not highly drought tolerant and should be watered year-round in the absence of rainfall. Drought, pollution, cold can stress or weaken Dogwood plants and cause them to become susceptible to insects or disease. Drought stress can first be noted in curled leaves and morning wilt. Newly planted trees should be deeply watered once per week.
PESTS AND DISEASES
Pests
Dogwood borers enter the trees through the bark. Bumps and cuts from the use of landscape equipment or other mechanical damage create opportunity for the borers. Keeping the trees healthy is a good way to keep down the risk of invasion. Indicators of borers are holes in the trunk, leaves that are smaller than normal and dieback of the crown.
The Dogwood club gall midge can also become a problem. Gall Midges causes galls at the branch tips. Leaves on these branches may be distorted and fail to form a flower bud. Prune out the galls as soon as they are discovered.
Leaf miners, scales and aphids can also take up residence in your dogwood. Use of horticultural oil, sprayed according to label directions will help to control or eliminate these pests.
Disease
Cornus florida is more likely to suffer from disease than Cornus kousa.
The two most prevalent diseases of Cornus florida are spot anthracnose and septoria leafspot.
Septoria Leafspot Spot Anthracnose
These diseases do not necessarily cause permanent damage, but interfere with the beauty of the tree. Left unchecked, disease may persist for multiple years and ultimately weaken and cause plant death.
The use of fungicides (Mancozeb, Daconil 2787 and Immunox) control septoria leafspot and spot anthracnose. Start at early spring bud swell. These foliage and flower diseases require a wet, humid environment during particular times of the year, especially in the early spring. Since weather conditions cannot be anticipated, it may be wise to follow a regular spray schedule for disease control.
Dogwoods are also quite susceptible to powdery mildew. Left unchecked this can weaken the plant and ultimately cause plant death. This fungus causes a white film on the leaves and leads to leaf curl and distortion. To prevent the fungus, foliage should be treated as it becomes fully expanded. To treat the disease, repeated applications of fungicide (Captan, Chlorothalonil, Horticultural Oil) may be required.
Dogwood anthracnose (discula) (not to be confused with spot anthracnose and not common) found on Cornus florida, discula will cause tree decline and eventual death. Immediate symptoms are purple bordered leaf spots and scorched tan spots. Control of this disease is difficult. Dogwoods that are planted adjacent to natural stands of native Dogwoods may be more susceptible to discula.
Necrotic Spot (discula) Blighted Leaves (discula)
MECHANICAL INJURY
It is important avoid damaging all trees, shrubs and other ornamentals with your lawn equipment. Wounds and cracks provide opportunity for disease and pests to enter and cause long-term problems.
CHEMICAL INJURY/OVER FERTILIZATION
Dogwoods and other ornamentals are very sensitive to herbicides. Be cautious when applying herbicide or fertilizer over the top of your tree’s root zone. The root systems of established dogwoods can be 3-5 times more extensive than the canopy.
Be conservative with fertilization. Dogwoods do not require frequent of high levels of fertilizer. Any general purpose fertilizer (16-4-8 or 12-4-8) can be used. Fertilize in late spring after new leaves emerge until early fall but avoid fertilization on trees stressed by drought in the summer months. A newly planted tree of 6’ in height will require only 4 tablespoons of fertilizer per application. For established trees, ½ pound (1 cup) per inch of trunk diameter (4 feet above ground level) in March and again in July is adequate. Increasing the application of fertilizer will not accelerate growth.
CONCLUSIONS
The graceful Dogwood is a spring pleasure to behold, and it treats us again in the fall with a change of color. Dogwood also plays an important role as wildlife habitat. Dogwood’s essential nutrients from foliage, twigs, leaves and fruit are enjoyed by waterfowl, game birds, songbirds and mammals such as deer, raccoons, opossums and even bears. Dedicate a space in your yard for this plant’s spring and fall color display.
Sources:
UNIVERSITY OF GEORGIA
OHIO STATE UNIVERSITY
UNIVERSITY OF TENNESSEE
Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database / USDA NRCS. 1995.
FLORIDATA
US ARMY CORPS OF ENGINEERS
Michael A. Dirr-MANUAL OF WOODY LANDSCAPE PLANTS
USDA Forest Service