Most taxonomists place viburnums in the Adoxaceae family, but others place them in the Caprifoliaceae of Viburnaceae families. Species are found in semi-tropical to cold-temperate climates in most parts of the world. Cool temperate species are usually deciduous while those found in warmer regions are evergreen. Small white or cream to pink flowers with five petals each are borne in spring in dense clusters with forms ranging from a rounded snowball shape to a flat form that may closely resemble the blossom of a lacecap hydrangea. Plant in the genus range from 2 to 30 feet tall, and growth habits are varied. Fruit is a spherical, oval, or somewhat flattened drupe that may be red, yellow, orange, pink, purple, blue, or black. Foliage textures may be velvety smooth, bold and rough-veined, or glossy and leathery. In some types attractive fall color is an extra bonus.
Growing conditions: Viburnums as a species are tolerant of many different growing conditions, but almost all of them grow well in moderately fertile, well-drained soil in full sun to partial shade. The species is exceptionally resistant to damage from insects and adapts well to a wide range of climates. For best fruit set, plant in groups of three to ensure cross pollination. Do your best to get viburnums that have some genetic variations and are not clones (vegetatively propagated plants from the same parent), as these result in the best flowering and fruit production.
Species: About 115 species and interspecific hybrids are recognized by most taxonomists. Some frequently grown selections are:
V. acerifolium (mapleleaf viburnum) produces flat-topped clusters of yellowish-white flowers followed by black fruit. Plants grow 3 to 6 feet tall and 3 to 4 feet wide and form loose, open colonies. This deciduous shrub is adapted to shade and dry soil and is hardy in Zones 3-8.
V. carlesii (Korean Spice viburnum) bears very fragrant hemispherical to spherical clusters of pink-tinged flowers in spring. Densely pubescent (hairy) dull gray-green to blue-green leaves with whitish undersides may turn bronzy in fall. Maturing to about 8 feet tall and wide, this shrub is dependably hardy in Zones 4-7.
V. cassinoides (Witherod viburnum or swamp blackhaw) sports creamy white, flat-topped clusters of flowers 2 to 5 inches wide. Fruit starts out green and turns to pink and then red to blue and finally black. It is particularly showy when all colors are present at one time. Expect swamp blackhaw to grow anywhere from 5 to 12 feet tall and wide and to be a useful, dependable shrub for gardeners in Zones 5-8.
V. dentatum (arrowwood viburnum) has creamy white lacecap flower clusters about 3 inches wide in spring. Unfortunately, they are unpleasantly scented. Fruit is a deep porcelain-blue to blue-purple color. This deciduous native tree grows 6 to 12 feet tall and wide in Zones 2-8.
V. ×juddii (Judd viburnum) surprises the gardener when white, fragrant semisnowball-shaped clusters of flowers open from crimson buds. Red fruit ripens to black. This deciduous shrub with wide, rounded habit grows anywhere from 1 to 10 feet tall and wide and is hardy in Zones 4-8.
V. opulus (European cranberrybush viburnum) has white flowers borne in lacecap type inflorescences with outer rings of showy sterile flowers and inner rings of fertile, inconspicuous flowers. Bright red fruit persists into winter and dries up like a raisin. This upright, spreading shrub, growing 8 to 12 feet tall and 10 to 15 feet wide, is invasive in Pennsylvania, Indiana, and Wisconsin. ‘Roseum' is the European snowball or Guelder-rose. All are hardy from Zones 3-8.
V. plicatum ‘Tomentosum' (doublefile viburnun) is at least a three-season favorite of many gardeners. White flower clusters bloom in spring followed by red fruit in mid-summer, and in fall the leaves turn an attractive red color. ‘Tomentosum Mariesi' has more compact form and bears larger flower clusters. The horizontal, spreading shape of the species topping out at 8 to 10 feet makes an attractive presentation in the garden. Grow it in gardens in Zones 5-9
V. tinus (laurestinus) has attractive, pink buds that open to form white clusters of flowers 2 to 4 inches wide followed by ovoid, metallic blue fruits that mature to black. Glossy green leaves are attractive, and gardeners near bodies of salt water find it useful for its moderate salt tolerance. Plants grow 6 to 12 feet tall and 5 to 10 feet wide and are hardy in Zones 7-10.
V. trilobum (American cranberry bush) is a deciduous, rounded shrub growing about 15 feet tall. Clusters of white flowers resembling lace-cap hydrangeas bloom in spring and are followed by red, edible fruits. Maple-like, dark green leaves turn shades of yellow, red, and purple in fall. ‘Wentworth' is an improved selection that fruits heavier than the species. American cranberry bush is hardy in Zones 2-7.
Showing Viburnum in Flower Shows
In Standard Flower Shows, viburnum can be exhibited as container-grown plants or as cut branches in the Arboreal Section. If you would like to exhibit a specimen in the next flower show, be aware that flower show judges will look for certain criteria. A high-scoring specimen will exhibit certain characteristics as outlined below.
- Branch exhibits are symmetrical or balanced in form with internodes closely or regularly spaced along the stem.
- Colors are bright and clear, and the plant is well hydrated and of firm substance.
- Texture varies according to type and may be smooth and glossy or dull and leathery, but should be consistent throughout the specimen.
- Berries, if present, are round, clustered at tips of branches, and may be variously colored depending on species. Whatever their color, berries should be full and plump.
- Flower clusters should be at their prime with about three-fourths open flowers and the remainder in buds and partially opened flowers.
- Flower clusters form at the tips of branches, and judges know that the form is dependent on species. They may be densely placed, small flowers, rounded clusters of showy flowers, or lacecap types with a combination of small center flowers surrounded with an outer circle of showy, infertile flowers.
- Branch should be well clothed with foliage, mature, and fully developed with no voids along the stem.
Faults for which judges will deduct points
- A branch that is asymmetrical, unbalanced, or has some leaves missing or gaps along the stem will be penalized as will branches with long internodes that indicate insufficient light.
- Dull colors, yellowing leaves, or brown edges on leaves are evidence of poor growing conditions or aging.
- Flowers that are wilting, losing substance, translucent around edges and overly mature with shedding petals deserve deductions.
- Of course, judges check for holes in leaves that are evidence of insect or mechanical damage or spots which evidence disease or cultural deficiencies.
The bottom line is, viburnums are attractive, useful shrubs in landscapes. If you just happen find a branch that is particularly beautiful when flower show time rolls around, consider cutting it and exhibiting it so that other gardeners in your area can be made aware of its beauty and usefulness in the landscape. Flower shows, after all, are educational events aimed at exhibiting plants and flowers that grow in gardens in the area. Take advantage or this regional resource.
(Mouse over pictures for identification and image credits. Thumbnail is Viburnum odoratissimum.)