Selecting Viburnums for the Home Garden

It is easy to be smitten by native viburnums, spying one in some botanical garden flowering in late May or early June, their flat-topped clusters of white, cream, or pink florets, their branches lush with greenery; most have toothed leaves, either coarse or fine, their texture glossy or matte. Seductively, berry-like drupes hang from their branches in late summer, first green turning pink to red, then some purple, some black. Each species varies. As fall pushes on, the leaves of viburnum also turn into a kaleidoscope of colors, distinct in the landscape.

Aside from their aesthetic qualities, which can make them the foundation for any pleasing garden, they are also supportive of wildlife. Many native viburnum host the larvae of the spring azure butterfly (Celastrina ladon) and the hummingbird clearwing moth (Hemaris thysbe). Viburnum flowers invite an array of Lepidoptera, along with other pollinators like flies, small bees, and scarab beetles. Drupes, high in lipids, are an important food source for both migrating and wintering birds, including hermit thrushes (Catharus guttatus), northern flickers (Colaptes auratus), cedar waxwings (Bombycilla cedrorum), and eastern bluebirds (Sialia sialis), along with many others. The shrubs also provide habitat and frequently shelter nests.

While they have been heralded as low-maintenance, easy to grow, and adaptable to many environments, my experience has been a little different. Several years ago, as a recently graduated Master Gardener and relatively new to gardening, I attempted to grow a single seedling of Viburnum cassinoides, formerly known as V. nudum var. cassinoides, and called by many common names, including northern wild raisin, possum-haw, and witherod.

The northern wild raisin was a perfectly healthy specimen acquired through the Master Watershed Stewardship Program. Unlike other shrubs I planted around the same time, such as buttonbushes (Cephalanthus occidentalis), a silky dogwood (Cornus amomum), and low-growing sumacs (Rhus aromatica 'Gro-Low'), the viburnum never took hold. It died within two or three years without ever blooming.

I thought I had done my research, apprised of the shrub's ideal growing conditions. I read on the Internet that V. cassinoides likes a wet habitat; full sun to partial shade; slightly acidic, loamy soil with a pH in the vicinity of 6.0; and is adapted to USDA Plant Hardiness Zones 5–9. I tried to evaluate why the shrub died. Did it lack enough light? Was its demise brought on by a particularly cold winter? Did the soil require more amending, or maybe the site, adjacent to a stream bed, needed to be more on the soggy side? I chalked up my setback as a learning experience.

I am currently planning a new garden, a plot of 1,200 square feet, securely fenced from deer, one designed to cater to pollinators and birds. The garden will take the shape of a mini meadow, naturalized with annuals and perennials that can accommodate occasional flooding. A few choice shrubs will be added in. While there is full sun, the soil is sandy and lean. I don't think V. cassinoides will work at this site because it isn't wet enough, but perhaps another native viburnum will.

The Lady Bird Johnson Wildflower Center lists 24 different species and varieties of viburnum growing in North America, most in the eastern United States. While many of these natives are well-known to arboretums and native nurseries, including a number of noteworthy cultivars, availability to the home gardener is mixed. Online nurseries broaden choice, but when it comes to shrubs, I like to inspect the health of the specimen I'm going to plant.

There are many considerations, including size, both height and width. Nannyberry (V. lentago) can reach 12–18 feet with a diameter of 6–12 feet. It can be grown as a bush or pruned into a small tree. Blackhaw (V. prunifolium) is also immense. It is found mostly in the southern half of the state. Both of these are attractive plants and have edible fruit, but they are too large for my space.

Mapleleaf viburnum (V. acerfolium) displays lobed leaves and is much smaller at 3–6 feet. It does well in dry shade. American highbush cranberry (V. opulus var. americanum) is large but not overwhelming, growing to about 13 feet. Its inflorescence is distinctive, having a pleasing lacecap appearance; a sterile ring of larger white petals surrounds a dense umbel. Hobblebush (V. lantanoides) is found in the northern parts of Pennsylvania. It is large and scrappy, preferring moist woods. Drooping branches root into the ground, hence its common name.

Southern arrowwood (V. dentatum) is the most versatile native viburnum I have investigated, averaging between 6 and 10 feet tall. It thrives in moist to average environments and is known for its adaptability to many cultural conditions. With a reputation for being tough, southern arrowwood can often be found in retail nurseries.

One of the trickier aspects of viburnums is understanding their sexual reproduction. Viburnum spp. is generally considered to be self-incompatible. Although they are monoecious, possessing perfect flowers with both male and female parts, in all likelihood, flowers on a singular plant will not develop into fruit, or at least not much fruit. Plants that exhibit self-incompatibility possess a gene that creates a chemical barrier, prohibiting their pollen from fertilizing the ovules. Self-incompatibility is a natural limitation that helps ensure genetic diversity and prevents inbreeding. One plant, under ideal conditions, will produce a spattering of drupes. Some species even seem to be less self-incompatible than others. To produce not just flowers but a reasonable amount of fruit, however, two or more viburnum, usually of the same species, but sometimes even different species, must be grown together in relative proximity. It is also critical that the blooms on these different shrubs occur at the same time or at least overlap. This helps explain why landscapers like to plant Viburnum spp. as hedges or in hedgerows.

There's another caveat. These two or more plants bearing multiple sets of simultaneous blooms cannot be genetically identical. They cannot be clones of one another, which is what occurs when plants are grown asexually in wholesale nurseries from vegetative cuttings taken from the same mother plant. Each shrub must be a discrete, genetically unique individual, typically achieved when a plant is grown from seed (apparently not so easy with viburnum, as its seeds have a complex double-dormancy scheme). Genetic diversity can also be achieved when at least one plant is a different cultivar from another. How then is the feat of selective breeding most easily accomplished? One potentially successful stratagem is to acquire plants from different nurseries. Keep in mind that some garden centers might not be forthcoming or even knowledgeable about these shrubs requiring cross-pollination. When deciding upon which viburnum species to grow, it is helpful to know the provenance of each specimen as well as its bloom times.

Some growers have attempted to tackle the self-incompatibility issue head-on. In 2022, Proven Winners developed Viburnum Glitters & Glows®. Two varieties of arrowwood (V. dentatum var. deamii) plants are sold together in one liner and are able to cross-pollinate each other. That's according to Terri Collins, the Pennsylvania representative for Spring Meadow Nursery in Michigan, a wholesale nursery that specializes in flowering shrubs. I also explored the Proven Winners Internet chat, not with an AI bot, but a real person on the other end of that chat named Cori B. This two shrubs in one liner method is similar to how some dioecious plants are sold together, both a male and a female, like holly, Ilex spp.

Next, I stumbled across the phone number of a nurseryman in Nebraska. For years, Gary Ladman ran a business called Classic Viburnums, specializing in both exotic and native selections. He is now retired but is well-versed on viburnum, both as a horticulturist and a breeder. Ladman is known for having produced a natural cross between V. prunifolium x V. rufidulum, resulting in ‘Prairie Classic'. One exemplar stands on the campus of the University of Nebraska-Lincoln.

We talked for an hour, mostly about two charts he emailed to me: an inter-species pollination chart, designating which viburnum shrubs are compatible with each other, developed through years of research at both Harvard and Yale Universities; and a bloom chart he had configured based on his own studied observations of many species and cultivars, from bloom to petal fall. If I were concerned about my sandy soil lacking fertility, he recommended using an acidic fertilizer designed for rhododendrons and azaleas. "Viburnums are adaptable," he said. "They won't croak on you." I didn't mention my experience with V. cassinoides. If it was fruit for birds I desired, he claimed from his own experience that arrowwood was the most prodigious.

There's still so much I need to learn about viburnums, like their growth rate, or how and when to prune them, if ever, given they grow on old wood. Then there is the issue of pests. One in particular, the invasive and highly destructive viburnum leaf beetle (Pyrrthalta viburni) favors V. dentatum. It has been identified in many Pennsylvania counties.

Despite their seductive powers and the value to wildlife that viburnums offer, I'm still not sure they are the best fit for my new garden. I might plant a safer bet, like shadbush (Amelanchier canadensis) and a cultivar of red chokeberry (Aronia arbutifolia 'Brilliantissima'). These are lovely small trees, more tailored to my attempt at landscape restoration. I will plan another adventure to utilize native viburnums.