Horticulture/Cornus florida

The Flowering Dogwood (also called American Dogwood, Cornelian Tree, False Box, False Boxwood, Florida Dogwood, Indian Arrowwood, Nature's Mistake or, White Cornel; Cornus florida, syn. Benthamidia florida) is a species of dogwood native to eastern North America, from southern Maine west to southern Ontario and eastern Kansas, and south to northern Florida and eastern Texas, with a disjunct population in eastern Mexico in Nuevo León and Veracruz.

Description
It is a small deciduous tree growing to 10 m high, with a trunk diameter of up to 30 cm. The leaves are opposite, simple acute oval, 6–13 cm long and 4–6 cm broad, with an apparently entire margin (actually very finely toothed, under a lens); they turn a rich red-brown in fall.

The flowers are individually small and inconspicuous, with four greenish-yellow petals 4 mm long. Around 20 flowers are produced in a dense, rounded, cymes 1–2 cm diameter, the flower head surrounded by four conspicuous large white or pink "petals" (actually bracts), each bract 3 cm long and 2.5 cm broad, rounded, and with a distinct notch at the apex. The flowers are bisexual.

While most of the wild trees have white bracts, some selected cultivars of this tree also have pink bracts, some even almost a true red. They typically flower in early April in the southern part of their range, to late April or early May in northern and high altitude areas. The similar Kousa Dogwood (../Cornus kousa/), native to Asia, flowers about a month later.

The fruit is a cluster of three to eight 10–15 mm diameter drupes which ripen to a bright red in the fall; they are eaten by birds which distribute the seeds. The berries are edible, often being used to sweeten tea in Mexico.

Growing conditions
Flowering Dogwood does best when it has shade from the west but good morning sun. It does not do well when exposed to intense heat sources such as adjacent parking lots or air conditioning compressors. It has a low tolerance of salt. In eastern North America, it is cultivated as far north as Toronto and south to central Florida. Farther west, places of cultivation include Boulder, Sacramento and Vancouver. It is sold in other temperate parts of the world, including Sydney, Australia.

Varieties

 * Cornus florida subsp. florida. Eastern United States, southeastern Canada (Ontario).
 * Cornus florida subsp. urbiniana (syn. Cornus urbiniana). Eastern Mexico (Nuevo León, Veracruz).
 * 'Autumn Gold' - white bracts; yellow fall color.
 * 'Barton' - large white bracts; blooms at early age; resists mildew.
 * 'Bay Beauty' - double white bracts; resists heat and drought; good for Deep South.
 * 'Cherokee Daybreak' - white bract; vigorous grower with variegated leaves.
 * 'Cherokee Chief' - red bracts; red new growth.
 * 'Cherokee Sunset' - purplish-red bracts; variegated foliage.
 * 'Gulf Coast Pink' - best pink flowering dogwood in Florida.
 * 'Hohman's Gold' - white bracts; variegated foliage.
 * 'Plena' - double white bracts; anthracnose-resistant.
 * 'Purple Glory' - red bracts; purple foliage; anthracnose-resistant.
 * var. rubra has pink flowers
 * 'Weaver White' - large white blooms; large leaves; candelabra shape; good in north-central Florida.

Propagation
Cornus florida is easily propagated by seeds, which are sown in the fall into prepared rows of sawdust or sand, and emerge in the spring. Germination rates for good clean seed should be near 100% if seed dormancy is first overcome by cold stratification treatments for 90 to 120 days at 4 °C (39 °F).[4][5] Flowering dogwood demonstrates gametophytic self-incompatibility, meaning that the plants can’t self-fertilize. This is important for breeding programs as it means that it is not necessary to emasculate (remove the anthers from) C. florida flowers before making controlled cross-pollinations. These pollinations should be repeated every other day, as the flowers must be cross-pollinated within one or two days of opening for pollinations to be effective.[6]

Softwood cuttings taken in late spring or early summer from new growth can be rooted under mist if treated with 8,000 to 10,000 ppm indole-3-butyric acid (IBA). In cold climates, potted cuttings must be kept in heated cold frames or polyhouses the following winter to maintain temperatures between 0 and 7 °C. Although rooting success can be as high as 50-85%, this technique is not commonly used by commercial growers. Rather, selected cultivars are generally propagated by T-budding in late summer or by whip grafting in the greenhouse in winter onto seedling rootstock.[5][7]

Micropropagation of flowering dogwood is now used in breeding programs aiming to incorporate resistance to dogwood anthracnose and powdery mildew into horticulturally and economically important cultivars. Nodal (axillary bud) sections are established in a culture of Woody Plant Medium (WPM) amended with 4.4 μM 6-Benzyladenine (BA) to promote shoot growth.[8] Rooting of up to 83% can be obtained when 5-7 week-old microshoots are then transferred to WPM amended with 4.9 μM IBA.[9]

Pests and diseases
It is very susceptible to dogwood anthracnose, a disease caused by the fungus ../Discula destructiva/. This has killed many wild stocks of Flowering Dogwood; domestic landscape plantings have often been affected to a lesser degree because better air circulation and less humid conditions discourages the fungus, but losses still occur frequently. The Kousa Dogwood (../Cornus kousa/) is more resistant to this disease, and sometimes planted as a safer alternative.