Viburnum

In many gardens, shrubs serve as the key element in structure and permanence. While evergreen species are often considered superior in these roles, many deciduous shrubs can be just as valuable. Viburnum species, a group of more than 150 evergreen, semi-evergreen and deciduous woody plants from the Adoxaceae family, easily contribute to garden structure with their interesting foliage, seasonal flowers, colorful fruits or berries, and, in many cases, stunning fall color that can be one of the highlights of the late-season landscape. 

Native mostly to Northern temperate zones, some viburnums also hail from South America and Southeast Asia. Various species are frequently planted in Mediterranean areas such as Sonoma County, but they are not drought tolerant and require adequate moisture during our hot, dry summers.

Viburnums are not fussy. They can be grown in just about any location be it sun or part shade; however, sun is preferable for flower and seed production. Most prefer moderately fertile and moist, well-drained soil.

Leaf texture varies from species to species; some are soft and toothed while others are leathery and glossy with smooth margins. They can have lacecap, domed, or snowball-shaped flower clusters, creamy white to pink-flushed. Some varieties need another viburnum pollinator close by to produce a good showing of berries that may be dark red to blue to black, all appealing to wildlife. 

Many viburnums grow to about 4-6 feet in height with about a 4-foot spread, although some, such as V. sargentii and V. opulus, can reach nearly 20 feet or the height of a small tree. A few dwarf varieties such V. opulus ‘Nanum’ are less than 3 feet.

Viburnums do not require regular pruning. However, it is wise to cut back vigorous shoots for preferred balance and shape in early- to mid-summer. Do not deadhead or the plant will not produce its charming berries.  

Viburnum tinus ‘Spring Bouquet’ is aptly named, as its blooms are most abundant in late winter and early spring. They begin as pale pink buds that open into tight, 2-4 in. clusters of tiny, fragrant white flowers. Small lavender-to-deep-purple berries accompany the flowers which bloom periodically throughout the year. It is this succession of buds, blooms and berries that is so attractive to birds, bees and butterflies. Thus, if the viburnums are threatened by an infestation of aphids, to which they are often prone, the birds can be of help in removing them. However, if all does not go accordingly to Nature’s plan, spray the pests with a strong stream of water or give them a dose of Neem oil. It also bears mentioning that this viburnum species is deer resistant.  

Because of its dense foliage compared to other viburnums, Viburnum tinus—or laurustinus as it is often called—makes an excellent hedge, foundation planting or even a single specimen. Note that ‘Spring Bouquet’ is a lower-growing cultivar of the plain species, V. tinus, that grows much taller to 10 ft. or more.

Long-blooming Viburnum plicatum var. tomentosum ‘Summer Snowflake’ or doublefile viburnum has a mature height and width of 4-8 ft. tall and wide. The 1½-to 2-in. lacecap clusters of white flowers are perched along the shrub’s horizontally tiered branches from June through September. Berries age from red to black; foliage changes from deep orange to burgundy red in autumn.

Other cultivars of doublefile Viburnum plicatum var. tomentosum that are truly show-stoppers with their graceful, outstretched spread of horizontal branches include ‘Mariesii’, a deciduous shrub with a moderate growth rate, green oval leaves that turn red in the fall and large flat-headed white flowers; and ‘Shasta’, with abundant, large, white, lacecap flowers, bright red fruit and maroon foliage in the fall. Both of these cultivars, however, have shorter bloom periods and are twice the size of ‘Summer Snowflake.’

Viburnum macrocephalum (syn. V. m. ‘Sterile’), Chinese snowball, is evergreen or semi-evergreen with clusters of large snowball-shaped flowers in spring, lime green initially before turning pure white. This shrub likes sun to partial shade, well-drained soil and grows eventually to 12 ft. or more.

Viburnum carlesii, Korean spicebush, is deciduous and grows to 4-6 ft. high and wide. Snowball-like clusters of waxy flowers emerge pink, then gradually fade to white. Korean spicebush is noted for a heady, intoxicating fragrance, hence the common name. In late summer to fall, the red berries turn black. V. carlesii is tolerant of adverse conditions and is generally trouble-free.

Viburnum x burkwoodii is a hybrid between V. carlesii and V. utile. Often semi-evergreen in cooler microclimates of Sonoma County, it matures at about 6-8 ft. tall by 4-6 ft. across. Red or pink buds open to highly fragrant white flowers tinged with pink in mid-spring. Clusters of berries change from green to red to black by early autumn. Fall color varies from brilliant red to dull burgundy. Burkwood viburnum likes full sun to partial shade and prefers moist, well-drained, slightly acidic soils, but it is quite adaptable to poor soils and does withstand low water in a shaded site. 

Viburnum davidii is one of the few smaller evergreen viburnums, 3-4ft. high and wide at maturity. Its 4-6 in. deep green leaves curve downwards to reveal handsome etched veins. Foliage nearly covers all stems to impart a mounding effect. Bluish black fruits follow spring flower clusters. This species enjoys morning sun only and will burn in hot afternoon conditions.

January 2020