Viburnums - some native shrubs worth knowing
I have a great liking for Vibernum plants. I even named my company after them. In my view, these shrubs are not planted enough in Manitoba gardens. When the native species have sufficient space and a few hours of summer sun daily, they are a real plus in the landscape.
The viburnums are members of the honeysuckle family (called Caprifoliaceae), which also includes the elderberry (Sambucus), snowberry (Symphoricarpos), bush honeysuckle (Diervilla) and twinflower (Linnaea).
Manitoba’s four native viburnum species have superb fall colours in most years, and all produce berries that many bird species eagerly devour. One European species, the European snowball viburnum, is also planted in urban gardens here. Here is a brief look at the appearance and growing habits of these species.
Nannyberry (Viburnum lentago)
I think of nannyberry in its native aspen parkland habitat as the king of woody shrubs. Often, rather than a shrub, it is a small tree growing up to nine metres (30 feet) high. The natural range of nannyberries can extend as far north as Hudson’s Bay, covering most areas of Manitoba and reaching eastward to the eastern part of Quebec, south to Georgia and west to Colorado.
Only nannyberry, of the native Manitoba viburnums, has a flower bud at the tip of many of its twigs. The bud, lilac-pink in colour, produces white flower clusters or umbels in the spring. The base of the bud is globe-like and tapers to a long point, the most distinguishing feature of the plant in winter. Songbirds find its bluish black berries very attractive, but then they are attracted to the fruit of all viburnums. Nannyberry plants are often stripped of their fruit well before the end of winter.
To most humans, both the fruit and flowers of the nannyberry have an unpleasant smell, but I don’t feel that way. Nannyberries will grow almost anywhere including shade, but they take on their best form in full sunlight. Their fall leaf colours can be a vibrant purple-red.
Downy arrowwood (V. rafinesquianum)
This is the Manitoba native arrowwood and should not be confused with the southern arrowwood (V. dentatum) which is native to Minnesota and other areas south of Manitoba. The two species are so similar in appearance that they are hard to separate. Downy arrowwood leaves have a fuzzy texture underneath and a distinctive shape: they look like arrowheads. They have broad evenly spaced ‘teeth’ along their leaf margins.
First Nations peoples used the straight hard stems of the plant for the shafts of their arrows. The flowers and fruit are similar to those of the nannyberry. The two species grow in similar woodland edge and woodland opening locations, but downy arrowwood can tolerate more shade and it grows into very dense thickets at times.
It is, in fact, very difficult to find the native arrowwood and dentatum arrowwood isoften sold, in error, as a native species in tree nurseries and garden centres here.
A mass planting of downy arrowwood in a corner of the garden can give your yard tremendous visual appeal as well as attracting many species of birds.
Highbush cranberry (V. trilobum or V. opulus var. americanum)
This native Manitoba shrub likes to grow in open, wooded, somewhat poorly drained locations. The shrub can become very wide, often three metres or more, and reach about the same height. It is not as dense growing as the nannyberry and downy arrowwood: its branching habit is loosely organized and quite open.
Some years the highbush cranberry can produce prolific amounts of bright red berries. These berries are a great favourite of birds, and I must admit I dote on the ripe, somewhat astringent, berries as well. Some people become quite sick when they eat too many.
Like the nannyberry and downy arrowwood, the highbush cranberry thrives in prairie urban gardens in summer if there is some sun during the day. All viburnums grow better if they are not exposed to strong northerly winds during the winter.
Several varieties of highbush cranberry are sold in garden centres in Manitoba. It can be very difficult to distinguish between these varieties unless the flowers are visible and mature. ‘Garry Pink’, a Manitoba variety commonly sold here, makes a wonderful specimen planting with its dense leafy texture and prolific red berries. In cool wet weather the flower is pink and in dry weather it is white.
Low bush cranberry or squashberry (V. edule)
This is a common, straggly shrub found in rich, moist woodlands around the province. In fact, it grows across most regions of Canada and through Alaska. Because its habitat is shade, the plant rarely produces many flowers or fruit. Its red berrieslook like a smaller version of the highbush cranberry. It is not suitable for most urban gardens.
European snowball viburnum or 'Guelder Rose' (V. opulus ‘Roseum’)
This shrub is common around southern Manitoba but it is rare to find a great looking specimen. The best specimens have white flower balls about eight centimetres in diameter. The twigs and stems have a tendency to tip kill or die back from frost in winter. The shrubs require protection from north and northwest winds. They are not truly hardy for most Manitoba locations. The flowers are sterile and therefore do not produce fruit.
Alone among the viburnums growing in Manitoba, this species is widely infested with aphids and leaf curling mites, giving the leaves a very ragged appearance. The pests can usually be kept under control through the use of dormant oil sprays and by watering the underside of the leaves weekly with the jet setting of a hose.
I would appreciate hearing from anyone who believes they have a superb specimen of the plant.
For the interested reader, I can recommend Michael Dirr’s new book, Viburnums. It is published by Timber Press Ltd, in Portland, Ore. The book is very technical, especially in dealing with the breeding and propagation of viburnums, but Dirr peppers his writings with a number of interesting and amusing anecdotes. The photograph illustrations are outstanding.
Mike Allen is a consulting urban forester, certified ISA arborist and owner of Viburnum Tree Experts in Winnipeg.