By Kris R. Bachtell, Collections Director

Transcription

1 ARROWWOOD VIBURNUM Viburnum dentatum By Kris R. Bachtell, Collections Director As a group, viburnums are among the most useful plants in Midwestern landscapes. There are nearly 200 members of this genus native throughout the temperate and subtropical regions of the world, particularly in Asia and North America. Several dozen different viburnums are useful locally. With so many different types available, their ornamental characteristics and landscape uses vary considerably. Some members, such as Koreanspice viburnum (Viburnum carlesii) and doublefile viburnum (Viburnum plicatum f tomentosum) are known as "garden aristocrats" because they have showy flowers (the flowers of Koreanspice viburnum are also exceedingly fragrant), a well-defined structure, and a conservative growth rate. Others such as wayfaringtree viburnum (Viburnum lantana) and arrowwood viburnum (Viburnum den ta tum) are best described as "garden workhorses," because they have good ornamental features, are adaptable to several different uses, and are tolerant to a wide range of environmental conditions. The many other viburnums fall somewhere between these two categories. Native Range and Habitat Arrowwood viburnum is native to the eastern and southeastern United States. This includes the seaboard states east of the Appalachian Mountains south to northern Florida, westward to include much of Georgia and the southern portions of Alabama and Mississippi, and nearly all of Louisiana. This plant is highly variable--the native range given here includes plants that some taxonomists separate into different species and varieties.* Arrowwood viburnum occurs naturally in floodplain forests, stream banks, wet woodlands, bog edges, and low, wet, acid-sand habitats. It is commonly associated with other eastern U.S. wetland plants such as red maple (Acerrubrum), water tupelo, (Nyssa aquatica), inkberry (Ilex glabra), winterberry (Ilex verticillata), and buttonbush (Cephalanthus occidentalis). It commonly occurs in partially shaded habitats. Fernald, ii1 Gray's Manual of Botany, divides the species, describing the more southern, hairy members as southern arrowwood viburnum (Viburnum dentatum), and the more northern, less hairy members as northern arrowwood viburnum (Viburnum recognitum). 6

2 Plant Characteristics and Landscape Uses Arrowwood viburnum is a large deciduous shrub; mature plants possess a dense, upright arching form. In the wild, older specimens can reach ten to twelve feet (3 to 3.6 m) tall with a spread of eight to ten feet (2.4 to 3 m). In the landscape a 25 percent size reduction is easy to maintain through routine renewal pruning (the removal of the largest interior canes from the base of the plant). Strong vertical shoots frequently arise from the base after the plants are pruned. The common name -- arrowwood -- comes from the fact that native Americans frequently used these shoots as arrows. The leaves are oval to nearly rounded in shape with a distinctively toothed or dentate edge -- this 7

3 Thefruits ofarrowwood viburnum are eaten by birds soon after they ripen on the plant. This hedge at the Arboretum shows the attractive form this plant can take as a clipped hedge. 8 is the origin of dentatum, the species name. The leaves are lustrous green in summer and commonly a mixture of maroon, red, and yellow in fall. Some cultivar selections have been made for more consistent fall coloration and a more rounded, less leggy form; these will be described in greater detail later. In late May to early June, small white individual flowers are borne together in 2- to 4-inch (.6 to 1.2 cm) diameter, flat-topped clusters. These are held upright on short peduncles and are quite showy in front of the fresh green foliage. The flowers of this species are not fragrant. From mid-september through early October, the ink-blue fruits, about the size of a large pea, mature and display their attractive coloration. Although they are considered useful ornamental features, the fruits are frequently consumed so quickly by birds and small animals that their display is often short-lived. This plant is an excellent choice for landscapes that are created for wildlife forage and cover. Siting arrowwood viburnum in your landscape or garden is not difficult. It is one of the most adaptable of all viburnums. It tolerates most local conditions, except extreme wetness or dryness. During the record 1988 drought, several plants in the Arboretum collections experienced leaf scorch and partial defoliation, but have recovered well without significant dieback. It is quite tolerant of shade, although best flowering and fruiting will result in full to partially shaded locations. Plants are easily transplanted as bare-rooted, container-grown, or balled and burlapped specimens.

4 To be at its best, arrowwood viburnum needs room to develop its characteristic vase shape. Indeed, the most significant restriction to more widespread use is its large size. It is quite effective when used in groups of three or five plants as a mass, as a free-style hedge, or as a single specimen as a filler in a shrub border. Because of its shade tolerance, it has performed well at the Arboretum as a medium- to large-sized sheared hedge, although flowering and fruiting are reduced considerably. Because it can sucker from its base, it may have to be restricted from getting out of bounds. This suckering nature can be useful when it is planted as a hedge. Arrowwood viburnum has proven to be tolerant of salt-laden ocean spray and winter deicing compounds. Arrowwood viburnums grown from seed are highly variable; three clonal cultivar selections are being promoted by the Chicagoland Grows Plant Introduction Program. All three selections were originally made by Ralph Synnestvedt, Sr. of the Synnestvedt Nursery Company, Round Lake, Illinois. Northern Burgundy Arrowwood Viburnum (Viburnum dentatum 'Morton') This selection is broad, upright-rounded in habit, and has moderately glossy, darkgreen foliage. Fall color is a rich blend of wine red and Burgundy from late October through mid-november. Chicago Lustre Arrowwood Viburnum (Viburnum dentatum 'Synnestvedt') This plant originated at the Arboretum and was promoted by Mr. Synnestvedt in the mid-1970s. It is upright, rounded in habit with distinctively thick, dark green, glossy foliage throughout the growing season. Yellow fall color develops late in the fall season. Autumn Jazz Arrowwood Viburnum (Viburnum dentatum 'Ralph Senior') This selection offers a gracefully upright, vase-shaped habit that is accentuated by slightly pendulous, dark green foliage, and colorful red leafstalks. Fall color is an appealing kaleidoscopic blend of yellow, orange, red, and Burgundy during late October through November. This is the author's favorite selection. Propagation Arrowwood viburnum is relatively easy to propagate. For seed propagation, collect fruits before they are taken by birds. Soak the fruit in a sealed 9

5 plastic bag with a small amount of water at room temperature to soften them and make them easier to clean. Rub the softened fruit on a wire screen to extract the nearly round seeds. To germinate well, the seeds require a warm, moist treatment for 2 months followed by a cold (below 40 degrees F.) treatment of 3 months. To accomplish this, sow the seed in a wellprepared seed bed in fall shortly after they have been harvested and cleaned, or treat seed in a polyethylene bag with a small amount of moist peat moss and store at the appropriate temperature. As mentioned earlier, seedlings tend to be highly variable. This lack of uniformity is distracting when the resulting plants are used as a hedge. Cuttings root readily when treated with low to moderate levels of rooting hormone and placed in a high humidity environment. In the Chicago area, cuttings are usually taken in mid-june. Locations of Plants in the Arboretum Arrowwood viburnum is planted in many different collections and landscapes in the Arboretum. Refer to the Catalog of Woody Plant Collections, available at the information desk in the Visitor Center and the Sterling Morton Library for exact locations. 10