Wednesday, September 02, 2009

Versatile Viburnums for a Vibrant Landscape

Gardeners in the temperate zones of North America can select from hundreds of small trees and shrubs which will readily flourish in our climate. However, among all the choices there are only a handful of “must-have” species, with viburnum at the very top of that fairly short list.

There are approximately 200 species of viburnum worldwide, with more than 120 species in North America alone. Locally, in the Mid Atlantic region, our native landscape offers several absolutely dazzling specimens of viburnum that are suitable for almost every yard and situation, including Mapleleaf, Arrowwood, Possumhaw, and Blackhaw Viburnum (Viburnum acerifolium, V. dentatum, V. nudum, and V. prunifolium).

Michael Dirr at the University of Georgia writes in his landmark Manual of Woody Landscape Plants: “A garden without a viburnum is like life without music and art.” Dirr’s sentiment simply reflects the fact that it is difficult not to fall in love with viburnum. After all, we are talking about a species which is drought-tolerant and capable of handling dry soils, while it also thrives in moist, sometimes wet conditions.

The viburnum cited above will shine in either full sun of partial shade, making them ideal as either specimen plantings, or tucked in among other shrubs in a woodland garden.

Like most members of the Caprifoliaceae (honeysuckle) family, they are virtually pest-free and tolerant of pollution and harsh urban conditions. They can be trimmed and shaped to form an elegant privacy screen or hedge, or left alone to spread or “naturalize” across a wild, informal landscape.

But these noteworthy considerations are only horticultural nuts and bolts. Viburnums are easy to love because they are simply lovely.

Our native species all feature small white or creamy-white flowers appearing in flat-topped clusters or cymes roughly three or more inches wide. Actually, yellow stamens glowing against the white petals create the creamy color in both the Mapleleaf and Arrowwood shrubs. Some closely related viburnum species are even credited with pink or rosy blooms. The flowers typically appear in April through May, with each inflorescence lasting about two weeks.

But the show does not end in spring. While the flowering activity is somewhat reminiscent of our native dogwoods, the autumn foliage encore puts Cornus florida to shame. Depending on the species and growing conditions, fall leaf colors range from chartreuse and yellow, to orange, pink, red, burgundy and deepest purple. Moreover, the flowers will form drupes or berry-like fruits in attractive clusters from late summer through fall, which might last into winter, depending on avian appetites. The drupes range in color from a delicate porcelain-blue to purple and black.

Naturally, each of our featured viburnum have unique characteristics worth noting. For example, Mapleleaf Viburnum is decidedly a small multi-stemmed shrub, generally growing at a medium rate to between three and six feet high, with about the same spread or width. The species is known for its suckering ability, whereby shoots sprouting from the shrub’s base help it spread into a dense clump.

In fact, you might well consider planting a Mapleleaf for a hedge rather than turning to invasive species like privet, burning bush, or thorny barberry. Mapleleaf handles pruning easily, and can be kept in-bounds by mowing over tender suckers which might pop up in turf areas. This species can be easily propagated from cuttings taken between June and July. Buy just a couple of containerized plants and you can have a nursery-full in about a year.

Arrowwood is much like a big brother to Mapleleaf, sharing many of the former’s growth habits, although it can reach between eight and 13-feet in height, with branches arching out up between ten to 15-feet. Arrowwood also tends to grow in masses, making it another contender for a native hedgerow or screen.

Interestingly, many gardeners like to prune Arrowwood back to a single leader, encouraging it to behave more like a small specimen tree. Certainly its flowers, fruits, and autumn color establish it as a substitute for dogwoods, which are now under attack by fungal foes and insect-borers, and a fit companion for other woodland natives like Amelanchier and redbud.

Like all viburnum, Arrowwood is a phenomenal addition to any backyard wildlife habitat. However, as the shrub is “self-incompatible,” meaning that it cannot pollinate itself, you should plant at least several different specimens to ensure a dramatic and abundant display of fruit. The cedar waxwings, cardinals, and brown thrashers will thank you with a chorus of songs and whistles.

Arrowwood is also easily rooted, allowing you to propagate an entire shrub border from its ample supply of stout suckers. Indeed, the shoots sent up from the base of the shrub were so prized by Native Americans that they used them to make arrow shafts, from which this viburnum’s common name arises.

Possumhaw, also called Smooth Witherod, grows somewhat larger than Arrowwood, up to 20 feet, and can be decidedly more tree-like, featuring a rounded crown with a considerable spread. It also features long-stemmed, flat clusters of small, creamy white flowers which first start appearing in May.

The common name for this species denotes the popularity of its long, dangling clusters of fruits among opossums, although other small mammals such as squirrels, rabbits and chipmunks, as well as songbirds, make quite a feast from the half-inch long oval drupes, which start out green, quickly turning pink, and finally ripening to a dark blue or purplish-black and lasting throughout winter.

The species other common name, “withe-rod,” reflects that the tree’s smooth grayish-brown twigs are strong and flexible, and, in fact, were often twisted together to form a rope to gather together sheaves of wheat.

One of the more lovely features of Possumhaw are its waxy, dark green leaves, perhaps the glossiest of any viburnum, which turn to a rich cinnabar (cinnamon to scarlet) in autumn. ‘Winterthur’ is probably the most popular cultivar currently and commonly found, having a more compact form, growing to about six feet, with aromatic flowers in spring and brilliant red fall color.

The last selection is the largest and most versatile. Blackhaw is the most like a small tree, growing up to 21-feet or somewhat more. Although it also produces suckers and can be multi-stemmed, for the most part it is a slow-growing tree with a rounded crown and a thirst for moist and wet soils.

Blackhaw is the best choice for a stand-alone ornamental, and is a superior substitute for invasive and troublesome species such as Russian and Autumn Olive, Bradford Pear, and many of the other popular Asian pears and ornamental cherries.

Blackhaw can be also be used as a tall deciduous screen or hedge, much like hawthorns, to which this species is often compared. It takes well to transplanting, which is helpful should you need to thin out a too-dense hedgerow.

From dry upland slopes to soggy floodplains, viburnum can provide privacy, habitat, and year-round beauty, adapting to most every type of soil and exposure.

Copyright 2009, Joseph M. Keyser

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