Is there a tree more lovely in flower than the North American dogwood (Cornus florida)? Whether flowering with the classic white bracts, the stunning rubra bracts, or the less often seen pale, creamy rose-tinted bracts, our native dogwood never ceases to give pause for beauty given.
At this time of year when traveling along southern New England roadways we are graced by the beauty of the dogwood, dotting sunny roadside borders where meets the woodland edge. The bracts and flowers emerge before the leaves, serving only to heighten their loveliness. The fresh beauty of the bract-clad boughs is offset by the impressionistic symphony of neighboring tree foliage unfurling, shimmering in hues of apple green, chartruese, moss, and lime peel.
Discouragingly, many dogwoods in our region are inflicted with the lethal dogwood anthracnose. I believe the problem is exacerbated by the vast majority of information regarding growing flowering dogwoods, which suggests planting in part shade, and does not differentiate between gardening in the north versus gardening in the Midwest or northern Florida for that matter. If one lives in warmer regions south of New England, yes, perhaps it is possible to grow a healthy C. florida in partial shade.
Dogwood anthracnose is caused by the aptly named fungus Discula destructiva. It will typically kill an untreated Cornus florida within two to three years. As we look to nature for an answer, the native flowering dogwoods growing in the fertile, moist, friable soil of the Northeastern woodlands, as understory trees, are the trees most affected by anthracnose. Cornus florida growing in an open, sunny location are far less afflicted. What we learn from this lesson is to choose a location that has good air circulation and full sun. What we know is that Discula destructiva requires high humidity for infection; therefore trees planted in mesic sites in the shade are more susceptible than trees growing in xeric sites.
Discula destructiva is a soil born disease. Dogwood trees inflicted with anthracnose will begin to show signs of infection by dying from the bottom up. The lower branches will become twiggy and will not flower or leaf-out. This is the opposite of what you may see if a tree is losing foliage along the upper branches because of drought stress, for example. A tree that is stressed from lack of water or nutrients will, generally speaking, begin to show signs of trouble from the top down.
Our lovely Cornus florida var. rubra (my second go around with this species; the first was killed by anthracnose) shows signs of drought stress every year, usually during the dog days of late summer. I place the hose at the base of the tree, allowing water to gently flow overnight (never wet the foliage of a dogwood). Visibly, the tree will perk up. Typically this will need to be done every few days, until the next soaking rain. Any tree that is stressed from lack of water is more susceptible to disease. Along with monitoring our tree for drought stress, and because we plant densely beneath the tree’s boughs, I have found these measures, thus far, have served to prevent an outbreak of anthracnose.
Note how beautifully grows this dogwood. Despite the rain-soaked droopy bracts, you can see its gorgeous overall form. The level branches grow horizontally and there are no bald, twiggy areas.
bract – In botany, a bract is a leaf-like structure surrounding a flower or inflorescence. The colorful bracts of poinsettias, the hot pink bracts of bougainvillea, and the bracts of dogwoods are often mistaken for flower petals.