The story goes that President Ronald Reagan was riding his horse in the vicinity of Camp David, noticed that all the wild dogwoods were dying and asked for an explanation.
The response from government botanists was that the beloved dogwood, that living symbol of the American spring with its stellar white blossoms, was in dire straits. A fungal disease named dogwood anthracnose was sickening and ultimately killing the flowering dogwoods in Maryland’s Catoctin Mountain Park. Soon it would spread far and wide, from native populations to dogwood varieties in gardens.
A generation ago, it seemed that the dogwood might go the way of the American chestnut, rendered practically extinct by a new disease. But here’s the good news: The dogwood tree lives on in the form of new varieties and hybrids developed to resist the disease as well as a newer and entirely different ailment named powdery mildew. Many of these introductions bring new ornamental qualities that offer additional reasons to reacquaint yourself with this tree.
Hybridizers “had to rush to beat this thing because everyone loves a dogwood,” said Jimmy Testa, a horticulturist at Mount Cuba Center, a native-plant research and conservation garden in Hockessin, Del.
There are other native dogwood species, but none quite as special as the flowering dogwood (Cornus florida), which, with age, becomes valued not just for its spring blooms but also for its elegant habit of broad-tiered branches, fall color and fruit, and pretty, dark-gray, blocky bark. Under the dappled shadow of old shade trees that are beginning to leaf out, there is nothing quite like a flowering dogwood bursting into life in April.
If you want the native dogwood back in your garden, and your life, you have to make sure that you are buying a named variety known for its disease resistance. Here are some good choices:
Developed by plant scientists at the University of Tennessee, this line of dogwoods has several named varieties. The first, Appalachian Spring, is considered the standard-bearer for anthracnose resistance. Testa called it “hands down the number one cultivar you want to get.”
It was discovered at Catoctin in 1990 by the university’s Mark Windham as the one wildling with natural immunity to the fungus. He returned a year later with colleagues to take cuttings, from which all Appalachian Spring varieties today have been cloned. Ornamentally, it has unusually large leaves and berries, with good red fall color. It is “highly resistant to dogwood anthracnose,” Windham said, “and we keep getting reports that it is resistant to powdery mildew, although we have never claimed that.”
The other four varieties in the Appalachian series, however, have been developed specifically for mildew resistance. Kay’s Appalachian Mist produces blooms on young trees, and the bracts are conspicuously large and slightly overlapping, giving a rounder effect. Jean’s Appalachian Snow has large and immaculate white bracts. Appalachian Joy produces blooms with extra bracts to give a fuller floral effect. And Karen’s Appalachian Blush has large, floppy bracts with pink edges to the bloom, though that effect is lost if flowering coincides with precocious heat.
These are hybrids between the flowering dogwood and its shrubbier and more upright Asian counterpart, the kousa dogwood (Cornus kousa). They were developed by hybridizer Elwin Orton of Rutgers University, now retired. They are generally free of diseases but may not be desired by gardeners wanting the pure form of the native tree. The variety Ruth Ellen is said to have the closest look of the native species, but generally the other Stellar introductions are midway between the two species in their habit, flower shape and blooming period. They are sterile and don’t produce decorative berries, but are particularly showy in bloom.
Aurora is vigorous and upright with velvetlike bracts, rounded and overlapping. Constellation is another upright, vigorous hybrid, but with the kousa dogwood’s low branching habit and with bracts that are long and separated. Celestial has rounded bracts.
Another product of this program, Stellar Pink, is one of the few pink flowering dogwoods that is reliably free of disease.
Among pure Cornus florida varieties, Cherokee Brave is considered the most disease-resistant pink bloomer. It might get an attack of mildew one year in five and then be fine again, Windham said.
Orton’s successor at Rutgers, Thomas Molnar, is working on deep-pink flowering kousa types and recently introduced a variety named Scarlet Fire, with large, pointed, starlike bracts of an unusually intense fuchsia-pink color.
If you can find it, a double-flowered Cornus florida variety named Plena (or Pluribracteata) is disease-resistant but non-
One of the most popular dogwood varieties is another of Orton’s plants, named Venus, but it doesn’t have flowering dogwood in its lineage. Instead, it is a hybrid between another native species, the Pacific dogwood, and the kousa dogwood. It is popular with consumers for its enormous white bracts.
There are other varieties out there that might perform well if grown in the right location. I asked Testa which varieties performed badly for him — Mount Cuba is in the rolling hills north of Wilmington, Del. — and he named Cloud Nine, Purple Glory and Autumn Gold, all afflicted with anthracnose or mildew.
I asked Windham whether a homeowner should pick a variety resistant to mildew or anthracnose. He said if you live in lower elevations with a sunnier spot, choose one for mildew resistance. If you live in higher elevations, particularly near water, and the tree will be shaded, pick one that will fight off dogwood anthracnose. “In which case, I would be planting Appalachian Spring,” he said.
Flowering dogwoods have always been a little fussy to grow, but contemporary disease and pest pressures make optimum cultivation even more important.
Ideally, they should grow in a site that gets plenty of light but not full sun, such as an area that is sunny in the morning but shaded in the afternoon or below trees with a high leaf canopy. (Kousa dogwoods and their hybrids can take sunnier conditions.)
Dogwoods won’t tolerate boggy areas, nor will they like hot, dry locations in poor soil. To minimize powdery mildew, avoid planting in corners or other areas with poor air circulation.
Existing dogwoods — those that didn’t bite the dust — can give clues to proper location. Those in sites where the spring rains and dew burned off escaped the dogwood anthracnose. “We did a lot of research, and site location is tremendously important,” said Mark Windham, a plant pathologist at the University of Tennessee. Another key element, said Adria Bordas, the horticultural extension agent for Fairfax County, is whether the trees received pruning when young to permit an open and airy branch architecture. Diseased branches should also be removed to prevent the spread of both diseases.
The biggest threat facing new dogwoods is incorrect planting, Windham said. “They have very hard wood but very soft bark that will rot if clay soil is up against the trunk. It should be planted no deeper than what it was in the container. My advice is, after planting, you should be able to see the top of the top root. And then put some mulch over that,” he said.
Because flowering dogwoods hate drought, young plants should be watered regularly in their first two years until they are established, but not to the point where the soil stays wet. Once they are established, don’t overwater them. In periods of drought, a mature tree should receive five gallons of water weekly.
Avoid heavy wood mulches and do not pile mulch against the base of the trunk. Dress the root zone instead with an annual layer of shredded leaves or half-rotted leaf mold. This will break down to create the sort of woodland duff that dogwoods like.
Make sure that the site you choose has space enough to accommodate a tree that can grow 20 feet high and 25 feet across, i.e. not right next to a path or a wall.
If you want ground covers in the plant bed, various ferns, sedges, foamflower, creeping and wild blue phlox, and wood asters would make great complementary native perennials.