Viburnum–A Shrub for Many Settings

• By Susan Martin
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• October 2019-Vol.5 No.10
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• 3 Comments

I first noticed the beautiful fragrance of Koreanspice viburnum (Viburnum carlesii) planted as a hedge at a commercial site. The bushes were as tall as small trees and had an abundant display of reddish pink buds turning to white flowers. I knew that viburnums needed more hours of daily sun than available in our wooded yard, but I had to try one.  I brought home just one, not realizing that in this case more than one viburnum was necessary for fruiting, since no berries ever appeared. (More on this later.) Although the bush produced some flowers in the spring (more sun would have encouraged more blooms), there were no blue-black fruits in fall to attract birds.

WHY PLANT VIBURNUMS

Viburnum is a genus of about 150–175 species of flowering plants in the moschatel family Adoxaceae. (Viburnum was previously included in the honeysuckle family Caprifoliaceae.) Viburnums are evergreen or deciduous, depending on the species and the location. Most prefer sun, but some do well in partial shade. Their hardiness is well suited to the cold winters of USDA hardiness zone 7. They are adaptable to a range of soil types and moisture conditions. Most viburnums offer attractive foliage, with a variety of leaf size, texture, and color. Many species offer eye-catching fall color in red-orange, burgundy, or reddish-purple. White blooms appear in early spring or even in mid summer. By choosing selections with different bloom times, gardeners can assure a long flowering period. In fall, berries appear in long drupes in colors ranging from red to pink, darkening to blue or purple-black. The fruit are a good food source for small mammals and birds such as the Eastern Bluebird, Northern Flicker, Gray Catbird, and American Robin.  The berries of the blackhaw viburnum (V. prunifolium) can be made into preserves or eaten off the bush. Berries of the nanny berry (V. lentago) are also edible. Most viburnums are mainly disease and pest-resistant, although some are subject to the viburnum leaf beetle. Native viburnums are noted as having special value for native bees, and attract many different types of butterflies and moths. Some native viburnum species are larval hosts to the Spring Azure butterfly (Celastrina ladon). Caterpillars of the Hummingbird Clearing Moth (Hemaris thysbe) host on European cranberry bush (V. opulus).

With so many viburnum species to consider, in this article I will concentrate on viburnums native to Virginia. I will also address how many viburnums are needed to assure fruiting, and the local threat from the viburnum leaf beetle.

VIBURNUMS NATIVE TO VIRGINIA

V. dentatum (Arrowwood) Photo: Fritzflohrreynolds, Wikimedia Commons

Southern Arrowwood (V. dentatum) is a deciduous shrub native to eastern North America. In Virginia, it is found in the coastal plain, Piedmont, and mountain regions. Native Americans reportedly used the straight stems of this species for arrow shafts. This viburnum grows in USDA hardiness zones 3-8 and is adaptable to different soil types and moisture levels. Although it prefers moist loam, it can tolerate clay soil and is fairly drought resistant once established. It can grow in full or partial sun. It grows 6-10’ tall and wide but can reach 15’ in optimum conditions. It is a good candidate for hedges. White flowers are not fragrant but appear in flat-topped cymes about 4” across in May and June. Flowers give way to blue-black, berry-like drupes. Glossy green, ovate, toothed leaves produce fall colors that range from drab yellow to attractive shades of orange and red. Although not particularly showy, this is a reliable, cold-hardy bush tolerant of varying conditions with berries that provide food for both birds and small mammals. It is a larval host to the Blue Azure butterfly (Celastrina ladon).

V. lentago (Nannyberry) Photo: Keith Kanoti, Maine Forest Service, Wikimedia Commons

Nannyberry (V. lentago) is native to North America and in Virginia is found in the mountain area. It grows 12-18’ tall and 6-12’ wide with an open crown and arching branches. One explanation for the common name is that overripe berries have an unpleasant smell like wet wool. Another explanation is that nanny goats are more fond of the ripe berries than are billy goats. The shrub is drought tolerant, can flourish in full sun to partial shade, and can easily be gown in average soils. It thrives in USDA hardiness zones 2-8. In May, white flowers appear in clusters up to 3-5” across, and attract many pollinators. Nannyberry is also host to the Blue Azure butterfly. Variable fall color ranges from drab greenish-yellow to reddish-purple. Edible, blue-black, berry-like drupes hang in clusters from red stems. The berries often persist into winter and are attractive to birds and wildlife.

V. prunifolium (Blackhaw) Photo: David Stang, Wikimedia Commons

Smooth Blackhaw (V. prunifolium) is native to eastern and central North American in USDA hardiness zones 3-9. In Virginia, it is found in the coastal plain, Piedmont, and mountain regions. It is easily grown in average, dry-to-medium, well-drained soil and can tolerate drought. It prefers at least ½ day sunlight. Usually grown as a large, upright, multi-stemmed, deciduous shrub, it typically reaches a height of 12-15′ with a spread of 6-12′. When grown as a single trunk tree, it may reach a height of 30′. In May to June, white, non-fragrant flowers appear in flat-topped cymes up to 4.5” across. The blackhaw uniquely places it flowers above its leaves (while the flowers on many viburnums are nestled). The flowers are followed by yellow berries that turn blue-black in fall. Fruits are edible and may be eaten off the bush when ripe or used in jams and preserves. They are also favored by birds and small mammals. The astringent bark was formerly used medicinally. This durable and pest-free plant is especially valuable to bumble bees. Blackhaw can be used as a small specimen tree or large specimen shrub. It is also used as a border addition, as a tall hedge or screen, or as a background planting in a native garden.

V. nudum (Possumhaw) Photo: U.S. Botanic Garden, DC, Wikimedia Commons

Possumhaw (V. nudum), also commonly called smooth witherod or wild raisin, is native to the eastern and southeastern U.S., from Connecticut south to Florida and Louisiana. In Virginia, it is found in the mountain, Piedmont, and coastal plains regions. It grows in USDA hardiness zones 5-9. This rounded, multi-stemmed, upright-spreading, deciduous shrub typically grows in the wild to 5-12′ tall and wide but can attain 20′ in height. Although it prefers moist soil in full sun it will tolerate shade and can survive periods of drought. Small creamy-white flowers appear in April and May and are pollinated by many small insects, including hoverflies and sweat bees. The possumhaw is host to the Blue Azure butterfly. In late summer to early fall, flowers are followed by clusters of ovoid berries that change color as they ripen, from light pink to deep pink to blue to purplish-black. The berries are eaten by songbirds, grouse, wild turkeys, and squirrel. Glossy dark green leaves can turn an attractive maroon to dark red-purple in fall. Native to low woods, swamps and bogs, possumhaw is a good candidate for rain gardens. Be aware that this plant is moderately resistant to damage from deer. Cultivars such as ‘Bulk’, sold under the trade name of BRANDYWINE, are available in the nursery trade. Straight species can be found online.

V. acerifolium (Mapleleaf) Photo: Katja Schulz, Wikimedia Commons

Mapleleaf (V. acerifolium) is native to eastern North America from southwestern Quebec and Ontario south to northern Florida and eastern Texas. In Virginia, it is found in the coastal plain, Piedmont, and mountain regions and is able to do well in full shade and dry soils. It grows in USDA hardiness zones 4-8.  It grows mostly in acid soil of pH 5.0 to 6.5, but can tolerate up to 7.5. This low, densely branched shrub grows 4-6′ tall and 3-4′ wide. Small white flowers appear in flat-topped clusters 1.5-3” across in early summer, followed by red berries turning to purple then black. The fruit is a food source for many birds and small mammals; the flowers attract pollinators such as bees and butterflies. Mapleleaf is larval host to the Blue Azure butterfly. The upright shrub often ground suckers and grows in dense clumps. Bright- to dark-green, deciduous foliage, maple-like in shape, turns a distinctive purplish pink in fall, making this a very desirable native shrub.

HOW MANY VIBURNUMS DO I NEED TO PLANT?

This is an important question that I would like to answer simply and definitively, but there just isn’t enough information from the sources I’ve researched. First, let’s remind ourselves that flowering will occur whether or not pollination occurs. Pollination is necessary for fruiting, in this case, berry production. Now let’s review definitions. Monecious means that there are separate male and female parts on the same plant. The plant is self-fertile and you would only need one plant to produce fruit. Dioecious means that there are only flowers of one sex on a plant. You would therefore need one male and one female plant in order to reproduce.

Out of the five native viburnums covered in this article, Virginia Tech Dendrology identifies mapleleaf (V. acerifolium) as being monoecious; the other four natives are not identified as being either monoecious or dioecious. According to the New York Botanical Garden FAQ, “Viburnums are monoecious but you will get better fruits by planting plants from different sources. This is particularly true of V. davidii which is usually described as being dioecious.”

According to NCState Extension, “As a general rule of thumb, viburnums are not self-fertile. This means that you need two compatible plants to cross-pollinate to receive the maximum fruit production.  This does not mean that you can plant two of the same clone/cultivar and expect fruit (you need genetic diversity). Another critical requirement is that for pollination to occur, both plants have to be blooming at the same time.”

According to the Urban Forest Ecosystems Institute at California Polytechnic Institute, all 14 of the viburnum species included in their review were classified as monoecious, including the two native viburnums on their list, blackhaw and nannyberry.

So, where does all this leave us? You can’t tell if a plant is male or female unless it’s in flower, and even then I would need assistance. If you are interested in making sure your viburnums produce fruit, you could refer to the following blog which I found very helpful in explaining the issues and proposed solutions: “Native Viburnums and Cross-Pollination, What the Nursery Isn’t Telling You.”

A simplified summary of the blog:

Two genetically different plants of the same species should be planted in reasonably close proximity. And, those genetically different plants must be in bloom at the same time so that visiting insect pollinators can do their job. To ensure genetic diversity:

• Buy from a nursery that produces its plants from seeds.
• If this isn’t possible, purchase two or more straight species viburnums (of the same species) from different nurseries that source plants from different growers.
• Purchase different cultivars of the same species of viburnum. (Be aware that in the case of Viburnum dentatum, it is a bit more complicated, so see the blog)
• Purchase a straight species viburnum and a cultivar of the same species, which are in bud or bloom at the same time.

VIBURNUM LEAF BEETLE

Viburnum Leaf Beetle (Pyrrhalta virnum) is gradually coming to the Southeastern U.S. The beetle is native to Europe and was detected in Canada in 1947. The first report of its presence in the United States was in upstate New York State in 1996.  This pest has been on the move, eating viburnums from upstate New York to northern Pennsylvania to western Maryland. It feeds only on viburnum species.

According to the UMD extension, “There is a high probability that viburnum leaf beetle will spread and become established throughout a wide region in North America due to climatic similarities with its native habitat and the wide use of viburnum species in ornamental plantings. However, recent studies indicate that its southern expansion may be limited by mild winters, as the eggs require a prolonged chilling period to hatch. The beetles spread naturally by flight, and artificially through people moving infested nursery stock into non-infested areas.”

Viburnum leaf beetle adult Photo: Hectonichus, Wikimedia Commons

Viburnum leaf beetle larvae on V. dentatum (Arrowwood) Photo: Plant Image Library, Wikimedia Commons

Both adults and larvae consume native and exotic species of viburnum in natural and managed landscapes. Although they show a preference for species with little hair (pubescence) on the foliage, they severely damage many of the approximately 150 known species of viburnum. Dr. Paul Weston of Cornell University categorized commonly grown viburnums into highly susceptible (first to be attacked; generally destroyed within 3 years), susceptible (eventually destroyed), moderately susceptible (usually not destroyed), and resistant species (little or no feeding damage). Both arrowwood and possumhaw are highly susceptible; mapleleaf is susceptible; nannyberry and blackhaw are moderately susceptible. Most species in all groups suffer more feeding damage when grown in the shade. Refer to Dr. Weston’s list for information on other viburnums.

Although it does not appear that this pest is currently damaging viburnums in the Piedmont area, we should be aware of possible danger in the future. It’s noteworthy that climate change and its effect on moderating winter temperatures could affect the spread.

For readers who live in areas where the viburnum leaf beetle is a problem, please see the Cornell University  site for recommendations on control. There is also encouraging news from the New York State Integrated Pest Management Program about a decline in the population of the beetles in Upstate New York.

SOURCES

Virginia Tech Dendrology, https://dendro.cnre.vt.edu/dendrology/syllabus/factsheet.cfm?ID=91

*Charlottesville Area Tree Stewards, https://charlottesvilleareatreestewards.org/learn-about-trees/identify-trees/

*Source also includes Common Native Shrubs and Woody Vines of Virginia: Identification Guide Virginia Department of Forestry Paperback 2016

Inflorescences: How Flowers Are Arranged on the Stem, The Seed Site, http://theseedsite.co.uk/inflorescences.html

“Plants That Attract Butterflies,” The Morton Arboretum, https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/plants-attract-butterflies

Butterflies and Moths of North America, https://www.butterfliesandmoths.org/species/Celastrina-ladon

“The Joy of Butterfly Host Plants,” Lewis Ginter Botanical Garden, https://www.lewisginter.org/butterfly-host-plants/

“Plant of the Month – Revisiting Viburnum,” Weeder’s Digest, November, 2005,
whatcom.wsu.edu › documents › newsletter

“Q. Which garden shrubs are dioecious, necessitating planting both a male and a female plant in order to
get fruit?” NYBG, http://libanswers.nybg.org/faq/222836

“Plant Guide: Sun to Part Sun – Wet to Moist Soil,” PennState Extension, https://extension.psu.edu/plant-guide-sun-to-part-sun-wet-to-moist-soil

“Plant Guide: Sun to Part Sun – Dry to Moist Soil,” PennState Extension, https://extension.psu.edu/plant-guide-sun-to-part-sun-dry-to-moist-soil

“Classic Viburnums – A Plant for All Seasons,” http://www.classicviburnums.com/index.cfm/fuseaction/home.showpage/pageID/23/index.htm

Viburnums, Missouri Botanical Garden, https://www.missouribotanicalgarden.org/gardens-gardening/our-garden/notable-plant-collections/viburnums.aspx

Viburnum Nudum, North Carolina Extension Gardener Plant Toolbox, NC State Extension, https://plants.ces.ncsu.edu/plants/viburnum-nudum/

“Native Viburnums and Cross-Pollination, What the Nursery Isn’t Telling You,” EcogBlog with Kim Eierman, https://www.ecobeneficial.com/2018/12/native-viburnums-and-cross-pollination-what-the-nursery-isnt-telling-you/

“Possumhaw – April 2016 Wildflower of the Month,” John Clayton Chapter, Virginia Native Plant Society, https://vnps.org/johnclayton/2016/03/23/possumhaw-april-2016-wildflower-of-the-month/

SelecTree: Tree Detail, Urban Forests Ecosystems Institute, California Polytechnic Institute, https://selectree.calpoly.edu/tree-detail/viburnum-lentago

Exotic Pest Threats, Viburnum Leaf Beetle, University of Maryland Extension,
https://www.extension.umd.edu › sites › files › _docs › programs › ipmnet

Viburnum Leaf Beetle – Susceptibility to Infestation, Cornell University, Dr. Paul Weston, http://www.hort.cornell.edu/vlb/suscept.html

Featured Creatures–Viburnum Leaf Beetle, University of Florida, http://entnemdept.ufl.edu/creatures/orn/beetles/viburnum_leaf_beetle.htm

“Managing Viburnum Leaf Beetles,” Cornell University, Department of Horticulture, http://www.hort.cornell.edu/vlb/manage.html

Feature Photo: V. nudum (Possumhaw) by JB Johnny, own work.