Native Viburnums: Form and Function in the Landscape
In a finely-timed spring ritual, a vibrant host of warblers, tanagers and other songbirds have ridden the wave of emerging caterpillars northward to arrive--much to our delight-- in our local woods, fields and yards.
Yet as Doug Tallamy, author of Bringing Nature Home and The Living Landscape has so succinctly put it: we feed the birds in winter, but starve them in spring and summer. We put out seeds and suet, but we may not be providing them with what 96% of songbird species need to migrate or raise the next generation: caterpillars. Even those we think of as seed-eaters—chickadees, for example, or cardinals—feed their young almost exclusively on caterpillars.
Azalea sphinx caterpillar on blackhaw viburnum.
Successful leaf-munching entails adapting to the defensive chemicals created by plants—and readapting once the plants have responded in turn by tweaking those chemical defenses. This ancient process of coevolution between plant and caterpillar accounts for the limited range of food or “host” plants available to a caterpillar species, even within its native ecosystem. Nonnative plants that have not been a part of this adaptation process rarely participate in the propagation of native moths or butterflies. Among shrubs, for instance, the Asian Budleia, or butterfly bush, may provide nectar for adult lepidoptera, but offers exactly nothing to their larvae. This is the crux of the reason for including a variety of native plants in our gardens and landscapes.
Happily, there are plenty of shrubs indigenous to Indiana that provide not only leafy food for caterpillars, but nectar for pollinators, protective cover for wildlife, nesting sites for birds, and fruits that are relished by gamebirds, songbirds and mammals. Native shrubs in the genus Viburnum are among the most valuable for the amount of wildlife they support.
Viburnums are host plants for many caterpillars: spring azure and Baltimore checkerspot butterflies; the rose hook-tip moth (which eats only viburnum); two large pollinator moths, the hummingbird clearwing and azalea sphinx; and numerous little moths with appellations such as common pug, horrid zale, intractable Quaker-- ones we consider nuisances around the porch light in their adult forms, but which as larvae are the mainstay of bird diets in spring and summer.
Human aesthetics need not be sacrificed to function here--all our native viburnums feature conspicuous, frothy heads of white flowers in April or May. Their leaves come in a variety of attractive forms, and in autumn take on brilliant reddish hues, contrasting in most species with blue-black fruits. Nine viburnum species occur in Indiana, with the following four found in many counties throughout the state.
Southern arrowwood is adaptable to most soil types and a range of light conditions. Its coarsely serrate, deeply veined leaves make the shrub attractive even when not in full flower. An upright shrub that suckers freely from the base, its dense, “limby” structure makes it ideal for nesting birds, and the fruits are savored by wildlife.
Blackhaw is tolerant of many soil types and grows in both sun and shade. The leaves of this robust viburnum are notable for their bright red petioles and vivid fall color. This tall, handsome shrub is fast-growing and may sucker widely to form large thickets, so give it lots of room.
Nannyberry (above) is another tall, suckering viburnum. Its charming name comes from the resemblance of the bluish black fruits to goat droppings, i.e. nannyberries. This viburnum will adapt to upland sites, but is a good choice for poorly drained or wet areas, and can be grown in either shade or sun. It may be susceptible to mildew if not given adequate air circulation.
Mapleleaf viburnum is a lower-growing shrub that spreads slowly to form clonal thickets. Often found on wooded ridgetops, it tolerates dry shade, but adapts to a variety of soil and sun exposures. Its striking maple-like leaves are as downy-soft to the touch as a kitten’s ear; autumn tints range from apricot to rose. Its growth form makes it a good shrub for wildlife cover and nesting birds.
Of my viburnums, deer seem to browse arrowwood the most heavily. They also sampled nannyberry leaves when the shrubs were young, but there’s been nary a cervine nibble on the blackhaw. That’s just in my garden, however, and is in no way a guarantee of what deer may find palatable in the shrubbery next door! A new threat to be aware of is the European viburnum beetle, which can defoliate and kill native viburnums (remember the coevolution lesson above—our viburnums lack a chemical defense against these recently introduced insect larvae).
Carolina Chickadees feed their nestlings almost exclusively on caterpillars
and other insect larvae.
A sweet cacophony of bird song outside provides my soundtrack as I write this. It reminds me that even the tiny chickadees require over 9,000 caterpillars to raise a single brood, and that a native viburnum in the landscape greatly enhances their chances for success.