Viburnums: a must-have shrub for every garden, for every season

24. May 2021 by Isabelle Van Groeningen
Categories: About gardening, english, Spring | Tags: , | Leave a comment

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Viburnum plicatum 'Kilimanjaro' © Isabelle Van Groeningen

Flagge Deutschland für deutsche Übersetzung – auf Deutsch lesen – At long last spring is really on the way. This year it has been unusually slow to get going due to the low temperatures. The three days of warm weather have finally pushed the vegetation into growth. Perennials have shot up in the border, trees and shrubs have come into leaf and wherever you look, you see leaf- and flower buds about to open. The early-flowering evergreen shrub Pieris has had a remarkably long season this year with the elegantly displayed little bell-shaped flowers, and are now embarking on the production of  their colourful new leaf shoots. The crab apples are finally flowering. Our Malus ‘Evereste’ is three to four weeks later than usual. Rhododendrons are also coming into flower. The earlier large hybrids such as the pure white ‘Cunningham’s White’ is looking splendid right now, whilst many others are still tight in bud, waiting for their time later this month.

Viburnum © Isabelle Van Groeningen

Diversity of the genus Viburnum

Viburnums are gearing up for their moment of glory on the flowering stage. They contain some of our most attractive and valuable garden shrubs that can provide colour, structure and scent almost all year round. Of all plant genera, together with Cornus, Hydrangea, Prunus and Rhododendron, is  this definitely one of the most diverse and valuable plant groups for our gardens. Of over 200 different species, there are over 80 in cultivation. They are so varied, of distinctive habit and character, different flowering periods and different types of flower, that I would not be surprised if botanists decide to split them into different, new genera. There are several evergreen and semi-evergreen species, though some of these may suffer frost damage during severe winters.

Different types of flower

The flowers are mostly white, sometimes shaded pink. Some are a perfect rounded ball shape, resembling a classic hydrangea. Others, look more like lacecaps flowers, with a centre of small, insignificant fertile flowers, surrounded by a collar of rounded petals, that are flat and shaped like a saucer. Others consist of clusters of small, more tubular flowers. Many are strongly, deliciously scented.

Attractive fruits

Numerous species and cultivars will produce an attractive display of berries in the autumn. These range from round, bright red or yellow berries (Viburunum opulus) to shiny black (V. tinus) or shiny blue (Viburnum davidii). In most cases they will produce a better crop of berries if you plan several together, as they benefit from cross-pollination. V. davidii is dioecious, meaning the plants carry either male or female flowers, like in the common holly. One needs to have at least one male plant to ensure the female flowers can be pollinated and set seed.

Evergreen species and autumn colour

Most of the deciduous varieties have valuable autumn colour, ranging from shades of yellow and orange to dark red. The intensity will depend on how much sunshine the plant is exposed to. There are a number of good evergreen species, though some are less hardy than others. Viburnum rhytidophyllum is known to be robust, and has interestingly textured foliage, which is tinged coppery brown. Their drooping habit give an overall sad appearance I find. Most successful I have seen them planted as a multi-stemmed specimen, pruned into a domed cloud-shape. Viburnum tinus makes a dense, dark green early-flowering shrub, which can also be pruned to form a hedge. Beware, as they may suffer in harsh winters. Reaching 60-70cm, V. davidii is a useful low-growing plant, that lends itself well to edging paths and shrub borders, with handsomely textured foliage. Early-season clusters of white flowers emerging from red buds are followed by attractive metallic-blue fruits on female plants. V. x hillieri ‘Winton’ has interesting red leafstalks, a flurry of small white flowers and fruits turning red to black. It will grow about 2m tall.

Viburnum x hillieri © Isabelle Van Groeningen
Viburnum x hillieri

Excellent autumn colour, combined with attractive berries ranging from pink to blue to black, is to be found in the north-American species V. nudum. With a similar size as the above species, it is a useful shrub, particularly for moist shade on acid soils. Two interesting selections are V. nudum ‘Pink Beauty’ with pink flowers, and the white-flowered ‘Brandy Wine’.

Viburnum 'Eskimo' © Isabelle Van Groeningen
Viburnum ‘Eskimo’

The award-winning hybrid ‘Eskimo’ has large white rounded heads of small,  fragrant flowers that create a spectacular display in Mai.  It is semi-evergreen, much depending on the winter climate reaching 2m by 2m.

Early flowering Viburnum

One of the most valuable winter flowering shrubs is Viburnum x bodnantense. Most widely grown are the varieties ‘Dawn’ and ‘Charles Lamont’. The first is has small clusters of highly fragrant tubular flowers. The pink buds, that open to almost white flowers, whereas ‘Charles Lamont’ flowers darker and is more vigorous reaching 3 meters or more in height. All have an upright growing habit, sending up strong shoots from the base.

Over the years they will start arching over. I find this habit very convenient, as one can plant numerous other shade-loving plants underneath. They flower between November and early April, possibly losing their first set of flowers in the frost, but keeping a second set that will open up towards the end of winter. In mild winters, they flower non-stop. In early spring, Viburnum carlesii  comes into flower with its cushions of highly scented almost white flowers. This species can reach three to four meters but is slow growing, though the variety ‘Aurora’ has more vigour growing to 1,5-1,8 meters, with buds a lovely dark red colour. Crosses such as Viburnum x burkwoodii and V. x carlcephalon have resulted in easier, more vigorous plants, reaching about 2 meters, but have less strongly scented flowers and a looser habit. V. x burkwoodii ‘Anne Russel’ is a useful, compact small shrub of about 1,5 meters.  They all have a long flowering period into early summer. 

Particularly valuable early summer to summer flowering shrubs:

Viburnum opulus (Gewöhnlicher Schneeball)

Viburnum opulus frucht © Isabelle Van Groeningen
Viburnum opulus Frucht

This shrub has a wide distribution. Distinctive types occur throughout most of Europe into Asia, Parts of eastern China and Japan, and parts of the USA. In Europe it is the from V. opulus ssp. opulus, often found growing in hedgerows. It can grow up to 6 m, has flat disc-like flowers and very decorative bright red berries that will last long into winter, before they are eaten by birds. Several cultivars make excellent garden plants: V. opulus ‘Compactum’ has all the above assets, but will only grow up to about 2m tall and wide, flowers profusely and carries a good crop of fruit, making it ideal for smaller gardens. V. opulus ‘Roseum’ produces attractive round flowerheads with only sterile flowers which are very popular in the cut flower trade. We have a long love affair with shrub: we have been planting it in our gardens as early as the 16th century. V. opulus ‘Xanthocarpum’ is similar to the wild species, except that it fruits stay yellow.

Viburnum plicatum

Viburnum plicatum 'Watanabe' © Isabelle Van Groeningen
Viburnum plicatum ‘Watanabe’

This highly decorative shrub is native to China, Japan, Korea and Taiwan. Like V. opulus, it has the highly decorative lacecap-like flowers, where the fertile, insignificant flowers are surrounded by a collar of “pretty” petals that serve to attract insects. In Autumn their fruits will develop from red, to blue to near black. These are classified as Viburnum plicatum ssp. tomentosum.  

Viburnum plicatum 'Rotundifolium' © Isabelle Van Groeningen
Viburnum plicatum ‘Rotundifolium’

Like in the above species, there are a few selections with purely sterile flowers, that make round ball-shaped flowerheads. These are classified as Viburnum plicatum ssp. plicatum. ‘Grandiflorum’ will reach up to 3 meters. There is also ‘Newport’, ‘Sterilum’ and ‘Rotundifolium’ with similar flowers. ‘Popcorn’ is a great favourite as it is very floriferous, almost completely covering the 2,5m tall and wide shrub with white round flowers.  This selection is said to be particularly drought tolerant.

Best known, and an absolute garden-classic  in the lacecap type V. plicatum ssp. tomentosum is the impressive ‘Mariesii’, which produces horizontal branches, topped  in early summer with rows of white flowering discs. Its effect is just mesmerizing. This is definitely my all-time favourite shrub as it has a very elegant, impressive habit, but only if you have sufficient space for it to allow it to develop its natural habit without being impeded by neighbours. It was introduced from Japan in 1879. I once saw a very old one in a Cotswold garden, that was almost 4meters tall, and probably 5-6m wide. It was most impressive, but at the end of its life. Upon my next visit it had sadly gone. Slightly compacter, but at least as beautiful is ‘Rowallane’. This one has given rise to anther valuable variety ‘Dart’s Red Robin’ which is particularly richly fruiting. Some have particularly long flowering seasons, continuing their display well into summer: ‘Summer Snowflake’, ‘Watanabe’ and ‘Kilimanjaro’. These are also compacter in habit, making them suitable for smaller gardens. They do have the horizontally spreading branches, but they just do not reach out as far, and are therefore not quite as elegant. Another one is ‘Pink Beauty’ whose white flowers fade to pink. ‘Molly Schroeder’ has a gentle hue of pink throughout its flowering time and will also do well into late summer. Both of these will only grow to about 2-2,5 meter in height, and about 2 meters wide.

Other lacecap producing species are V. sargentii ‘Onondago’ which has attractively reddish bronze-coloured emerging foliage and makes a very manageable ca. 2 meter tall garden shrub.

Care

Viburnum is on the whole an easy shrub to grow. They tend to be unfussy about the type of soil they grow in. Most prefer a slightly alkaline soil, but perform equally well in a lower pH  and tend to prefer growing in sun or partial shade. They will be happiest, planted with a good helping of compost or leafmould that helps to retain moisture in the soil, but they dislike wet feet. During periods of excessive drought it is advisable to keep an eye out, they may need an occasional soaking. Especially when the plants are still relatively young. They do not require pruning, and are nicest when left to develop their natural, beautiful shape.

Viburnum plicatum 'Dart's red Robin' © Isabelle Van Groeningen
Viburnum plicatum ‘Dart’s red Robin’

It is hard to know which ones to choose. Ideally I would like to grow all of them, but for that I would need an arboretum.  A Viburnum x bodantense ‘Dawn’ is indispensable for winter, followed by one the earlies such as  Viburnum carlesii  ‘Aurora’. Without one of the beautiful horizontally growing lacecaps like  V. plicatum ssp. tomentosum ‘Rowallane’ or ‘Molly Schroeder’ and ‘Summer Snowflake’  I cannot live. Though I’m sure I will find space in my next, larger garden for on or two of the sterile forms, such as ‘Popcorn’, even though these forms make no contribution to wildlife. For autumn show I will add V. nudum ‘Pink Beauty’ with its glorious autumn colour and wonderful berries. It does not have to be an arboretum, but it will have to be a garden large enough to have all of those… I’d better start looking.

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