The Seed is the horticultural magazine of the Nebraska Statewide Arboretum. It is published twice a year for the members of the Arboretum. This issue was written by Karma Larsen. Copyright 2000. For a full version of this publication with visuals, photographs, charts, landscape designs, etc. call 402-472-2971.

The Seed, Spring 2000

Viburnums—A Nebraska Sampler

     The reasons for planting them are as varied as the plants themselves:
Koreanspice viburnum for the strong clovelike scent of its flowers; Mohawk viburnum for abundant red buds opening to white blossoms; blackhaw viburnum for glossy red fall foliage; doublefile viburnum for the strong horizontal tiering of its branches-noticeable year-round but most evident midwinter; allegheny viburnum for large, leathery leaves that may persist through the entire winter.
Most of them do well in shade or sun. They require very little maintenance, aren't particular about their surroundings, are susceptible to few pests, and all of them will offer several seasons of interest, regardless of the reason or season they were planted for.
     In spite of the multi-season appeal all viburnums have, we'll approach them by season, moving from the viburnums most prominent for spring blossoms and fragrance, to those known for their ornamental fruits, to the viburnums with the most colorful fall foliage, on into those with winter interest.
     Koreanspice viburnum (Viburnum carlesii ), probably more than any other member of this group, is known for its fragrance. The strong clovelike fragrance can be noticed several blocks away when its pink buds open to white flowers in late April. It is a rounded shrub with very stiff, upright branches. Besides spring fragrance, summer foliage is soft, very pubescent, and often turns wine red in the fall. It can tolerate full sun or partial shade in well-drained soil. This shrub was selected by the Nebraska Nursery & Landscape Association as the Plant of the Year in 1999. Somewhat susceptible to bacterial leaf spot and powdery mildew, the cultivars 'Cayuga' and "Compactum' are more resistant. 'Cayuga' is slightly more compact (5 x 5'). 'Compactum' grows to 3 x 3' and has very dark green foliage.
     The white flowers of burkwood viburnum (V. x burkwoodii ) are fragrant for a brief but worthwhile 7-10 days in April. The scent has been compared to winter daphne. Planting them in full sun increases flowering for this shrub. Fruits are sparse but may be likewise increased by planting other viburnums of the same species nearby for cross-pollination. It is more tolerant of heat and cold than many of the other fragrant viburnums and its leaves are glossy green.
The cultivar 'Mohawk' is known for several flowering traits: the abundance of inflorescences; their color-dark red buds opening to white flowers with red markings; and, since the buds appear several weeks before the flowers open, its extended period of spring color.
     Fragrant viburnum (V. x carlcephalum) has a wonderful scent and is one of the latest snowball-type viburnums to bloom, flowering in late April to early May. Its cold-tolerance in the northern half of Nebraska may be questionable.
The foliage of Judd viburnum (V. x juddii ) is almost blue-green. Fragrance is similar to that of Koreanspice viburnum and it's more heat-tolerant and less susceptible to bacterial leaf spot than many viburnums.
     Though not as fragrant as the previous viburnums, horticulturist Michael Dirr describes the leaves of Service viburnum (V. utile) as "a genetic gold mine for leaf gloss, color, small stature, heat tolerance."
     European cranberrybush viburnum (V. opulus) has both sterile and fertile flowers in the same inflorescence. The inner ring of sterile flowers has yellow anthers and the outer ring of white flowers is showy; the presence of both blossoms at the same time gives it a "pin-wheel effect." Fruits are bright red and persistent. Leaves may have fall color, but often fall off while still green. It can tolerate wet areas with poor drainage better than most viburnums. There are several good compact cultivars of European cranberrybush viburnum, 'Compactum' which, at 5 x 7', is about half the size; and 'Nanum' growing just 2 x 2.5' in height and width. 'Roseum' is popular in Nebraska, bearing profuse flowers in May.
     Maxwell Arboretum, part of the University of Nebraska-Lincoln Botanical Garden and Arboretum (UNLBGA) has an extensive viburnum collection. In the past, there were several European cranberrybush viburnums in that collection. But curator Jeff Culbertson prefers not to plant this variety and has removed many of the existing ones because of problems with aphids, which can badly deform the foliage mid-season.
     If you're planting viburnums for their fragrance, it's worthwhile to plant them close to the house or on a frequently-used walkway. There are a few viburnums that should not be planted close by; Siebold and Linden viburnums, for example, are two viburnums that are grown in spite of, not because of, their fragrance!
     Sargent viburnum (V. sargentii ) is similar to European cranberrybush.
Though somewhat coarse in appearance, it is more resistant to aphids. The cultivar 'Susquehanna' has a corky trunk and dark green, leathery foliage. It bears lots of flowers and attractive red changing to black fruits, which are favored by birds.
     The fruits of Siebold viburnum (V. sieboldii ) are likewise spectacular, changing from rose to red to black. This is one of the largest viburnums, growing to 20' or higher. It has a rigid growing habit and is recommended for specimen planting. Donald Wyman says "If I were to choose only one viburnum for my garden, I think it would be this because of the splendid long (6") leaves, its very desirable branching habit, which results in rounded masses of foliage interspersed with open areas where lights and shadows add much interest, and its colorful fruits."
     American cranberrybush viburnum (V. trilobum) has large, flat-topped flowers, yellow to reddish purple fall foliage and bright red fruits that may hold from September into February. It is almost indistinguishable from European cranberrybush, but has better fall color and is more resistant to aphids. A dwarf cultivar, 'Compactum', grows to 5 x 5'.
     Nannyberry viburnum (V. lentago), a Nebraska native, is tolerant of almost any conditions; sun or shade, moist or dry soils, planted in a border or as a specimen. The flowers are white with yellow stamens, giving them a creamy appearance. Fruits go through a series of color changes. Green when they first appear in September, they may turn yellow, rose and pink before becoming bluish black. They often persist into December. Fall foliage may be red, but often the leaves fall off while they are still green. Its one weakness is susceptibility to mildew, so it should be planted where there is good air movement.
     The fruits of Arrowwood viburnum (V. dentatum) are also bluish black September through October and are favored by birds. Michael Dirr calls this viburnum "possibly [the] most durable viburnum for midwest…in Nebraska it withstands the high pH, heavy soils and the vagaries of that climate." The dark green leaves are glossy and turn yellow to red in the fall.
     On wayfaringtree (V. lantana) the fruits go from yellow to red to black, and often all three colors will be present at the same time, making it a showy plant in the fall even though its leaves rarely develop good fall color. Planting several varieties in close proximity will increase fruiting for this viburnum. It can also withstand difficult, clayey soils. The cultivar 'Mohican' is slightly smaller, 8.5 x 8.5', than the mature size of 13 x 13' for the species.
     Another viburnum outstanding for its fruits is linden viburnum (V. dilatatum). Drupes are bright, cherry red September through October, sometimes drying and persisting into December when they look like "withered red raisins." Its leaves also hold late and can turn a bronze or burgundy color.
     Mapleleaf viburnum (V. acerifolium) is one of the smaller viburnums,
growing 5 x 3.5'. Fall foliage is beautiful, ranging from pink to orange to purple. Spring flowers are yellowish white and fruits are black, often remaining into the winter. It can grow in almost full shade and, unlike most viburnums, can also tolerate dry conditions.
     Arrowwood viburnum (V. dentatum) can have beautiful glossy red to purple foliage but Dirr warns that "there is great variability within this species; I have seen poor fall colored specimens growing next to brilliant glossy red forms; the differences were not attributable to soils or climate but genetics." Fruits are bluish black and birds like them.
     One of the good viburnums for specimen planting is blackhaw viburnum (V. prunifolium). It looks very much like a hawthorn with its stiff, gray-brown upright branches, and it has good fall color. Flowers are white with yellow stamens and fruits go from pink to bluish black. It is similar to nannyberry viburnum but more resistant to mildew.
     Though its foliage doesn't tend to take on fall color, the dark green,
leathery leaves of lantanaphyllum viburnum, (V. x rhytidophylloides) persist into winter. The cultivar 'Alleghany' has somewhat smaller and even more persistent foliage. Inflorescences are yellowish white and fruits a bright red turning to black. The deeply ridged foliage of 'Willowwood' also may persist into the spring. Its branches have a slightly more arching habit.
     Leatherleaf viburnum (V. rhytidophyllum) is aptly named. Its leaves are sturdy with deep wrinkles, and if planted in a protected micro-climate, can be evergreen even in Nebraska. Flowers are yellowish white in mid-May, fruits red to black and possibly holding into December. This species is tolerant of hot, dry, sunny locations.
     We'll save one of the best for last. Dirr calls doublefile viburnum (V. plicatum) "possibly the most elegant of flowering shrubs." The strongly horizontal, tiered branches are evident even with full foliage. Mid-winter they really stand out. In spring, the pure white flowers are not particularly showy, but since they are borne in layers above the stratified foliage, they accentuate the horizontal habit of the branches. Fruits appear early, going from red to black in July and August, and are quickly devoured by birds.
     It flowers as well in shade as in sun and, since it is not very tolerant of heat and dry soils, should probably be planted as an understory shrub. Hardiness is zone 5 to 8, and it may be more susceptible to winterkill than the other viburnums. UNLBGA has two cultivars of V. plicatum var. tomentosum: 'Mariesii' and 'Shasta,' both of which have the strong tiered effect and abundant flowers lifted above the branches.
     The viburnum collection at UNLBGA, with a combined total of 1,263 viburnums on the two campuses, is probably the largest in the state. It was planted around 1979, curator Jeff Culbertson says. He thinks of viburnums "long-term, like trees. They'll be here a long time. As a group, they're a great plant. They have longevity, beauty, ease of maintenance."
     For the most part, viburnums need pruning only to repair damage, unlike forsythia and lilac which require regular pruning to keep flowering at its maximum. But as viburnums age they may require some pruning to restore the planting and ensure future growth. Most viburnums begin setting buds for the next year sometime in July or early August, so if you are planning to prune them and don't want to cut down on next year's blossoms, Culbertson recommends pruning sometime between May and August.
     Viburnums have a life cycle of at least 25 years and many of the viburnums at the Maxwell Arboretum had grown to a height of about 12' and then stopped putting on new growth, particularly lower growth. Because of that, for the last few years Culbertson has been gradually renovating or rejuvenating the shrubs by removing old wood and allowing new canes to take over, "one of the easiest ways to propagate them." But many of the viburnums will be cut back to 4-6" from the soil to allow for new growth.
     As far as planting, he recommends buying potted shrubs and applying a heavy mulch since they are a forest or edge species…"you can't find them in the Sandhills." He warns that the first year there won't be much growth, but "by the fifth year or so you may have an 8' shrub-they may grow 2' in a year after the first year or so." He believes Nebraska summers are harder on viburnums than the winters, so he recommends planting them in an east-facing site, where they are protected from late day summer sun.
     Because of poor performance, some viburnums are no longer planted at UNLBGA-European cranberrybush, for example, because of the damage aphids do to the foliage. He also avoids Southern blackhaw, which wasn't doing well. Mapleleaf viburnum he sees as marginal in Nebraska, unless they are well-protected and the soil is moist and well-drained. He warns that nannyberry needs good air movement or it will get mildew. Though Culbertson likes nannyberry and has seen some beautiful specimens at the Chicago Botanic Garden, the ones planted at UNLBGA have tended to sucker.
     As far as personal preferences, his favorites are doublefile viburnum for its form and flowers, particularly 'Shasta'. He also likes the flowers of Koreanspice viburnum. For persistent fruit, he recommends American cranberrybush viburnum which seems to be a last choice for birds.
     Gardeners have their own reasons for the selections they make. They
may want color, fragrance, shelter, habitat for birds… And every garden offers its own constraints in terms of shade, soil, air movement, etc. Though this listing is only an outline, here are some of the characteristics and preferences you might want to keep in mind in selecting a viburnum:
♦If the site is in heavy shade, mapleleaf and arrowwood viburnum are good choices.
♦For dry soils, possibilities include nannyberry and mapleleaf viburnums. Arrowwood viburnum can withstand heat better than most varieties.
♦To attract wildlife, the fruits of nannyberry, Koreanspice, arrowwood, Sargent and American cranberrybush viburnum are favored by birds. Any of these shrubs will be useful in a butterfly garden. On the other hand, if deer are a problem in your locale, viburnums are rarely bothered by them.
♦For specimen planting, some of the larger and more interesting ones include: wayfaringtree, nannyberry, doublefile, blackhaw and Siebold viburnums.
♦If the site is wet, European cranberrybush viburnum will do well.
♦For persistent fruit, you might want to try linden and American cranberrybush viburnum.
Michael Dirr says "A garden without a viburnum is akin to life without music and art." No matter why you plant them, viburnums will surprise you by offering something you hadn't expected.