Viburnums are an essential plant for the winter garden
Viburnums are an essential shrub for the winter garden, giving much needed scent and flower when there is little else. They are evergreen or deciduous shrubs, with approximately 150 – 175 species, and are native to mountainous regions in South America, the Atlas Mountains and the temperate northern hemisphere. The deciduous species tend to come from cool temperate regions and the evergreens from warmer areas. They are fully hardy and easy to care for, being virtually maintenance free, if they are planted in the correct position. Their fragrant flowers in cream, pink or white appear in clusters over winter and spring. Many of them have poisonous berries, which can be red, blue or black, so bear this in mind if you have small children. They are a good plant to incorporate in a mixed or a wildlife hedge as the birds love the berries.
They need to be pollinated in order to produce berries, so you need 2 plants of the same species. This should not be necessary in an urban garden as it is almost certain that there will be one in someone else’s garden nearby. They look fantastic in a woodland garden planted with hellebores, cyclamen and pink and dark purple tulips.
Viburnum plicatum f. plicatum 'Grandiflora' (Japanese Snowball)
Position
They like a cool root run so avoid a hot dry position. They like moist, well-drained fertile soil and don’t mind if it is in full sun or partial shade. The fragrance is stronger when the temperature is warmer so, if possible, plant where it will receive the afternoon sun when it is in flower. They prefer a neutral pH of 5.6 – 6.6, but will tolerate a more limey soil rather than more acidic. They can be grown in containers but it must be fairly large and they are more labour intensive. They soon exhaust their food supply so must be fed and re-potted regularly. They also tend to have a shorter life-span and suffer more stress which can make them vulnerable to pests and diseases than if they are planted in the ground.
Planting
When planting put a good couple of spades full of peat-free multi-purpose or home-made compost in the planting hole. They dislike heavy clay soil so if possible avoid planting them in this type of soil; if it is unavoidable then improve the soil by adding plenty of horticultural grit and peat-free compost which has a large structure. Adding a little mini-chip bark will also open up the soil structure and improve drainage. Plant to the same depth as the plant is in the pot. Water after planting, then mulch (5cm, 2” thick) with chipped bark, to retain moisture and suppress the weeds.
Aftercare
Water well for the first year after planting. In spring give them a feed of slow-release balanced fertiliser. Renew the mulch every 3 years.
Pruning
They do not need pruning; so just take out any diseased branches or open up the centre to improve airflow in early summer.
Viburnum tinus 'Lisa Rose'
Pests and diseases
Viburnums are generally pest and disease free, trouble usually occurs when the plants are under stress; lack of water, too much water in poorly drained soil or lack of nutrients.
Fungal leaf spot appears as black spots on the leaves. Try and avoid overhead irrigation and improve the air-flow around the plant by pruning out some of the centre of the plant if it becomes congested. Space plants out, don’t plant them too close together and prune out any over-hanging tree branches. Raking up and destroying any infected leaves (do not compost) will minimise chances of it recurring the following year. Spray every 10 – 14 days to keep the fungus in check.
Algal leaf spot occurs in cool damp conditions and appears as pale green spots on the leaves, becoming browner with age. Treat as for fungal leaf spot.
Powdery mildew occurs when conditions are dry, warm and humid and are worse on plants in the shade. It appears as white – light grey patches on the upper side of the leaves. Improve air circulation and spray with a fungicide, avoiding any with a sulphur component as it is detrimental to viburnums. Prune out any heavy infections and rake up and destroy the infected material.
Downy mildew usually occurs in cool warm weather with wet periods. It appears as light green patches on the upper leaf and white – light grey on the lower leaf. Treat as for powdery mildew, making sure you also spray the underside of the leaves.
Die-back and canker are the result of a fungal infection resulting from pruning wounds and injuries to the bark, and is exacerbated by drought stress. The fungus prevents water from travelling up the stem and results in the top of the shrub wilting then turning brown. There is no chemical treatment. Prune the infected branch back to healthy growth. Dispose of the material (do not compost). Make sure you disinfect your pruners.
Aphids are occasionally attracted to the soft new growth resulting in twisted and distorted leaves. Spray with a mixture of washing-up liquid and water, a strong jet of water to dislodge them or a systemic insecticide every 5 – 7 days. If the infestation is light just rub them off between finger and thumb.
Scale insects are flat, brown disc shaped insects. The first sign of an infestation is often the presence of black, sooty fungus which lives on the honey dew secreted by the scale insect. If the sooty fungus is widespread it may be necessary to treat that first, as any spray for the scale insect may not get through to the leaf. Either spray with a fungicide or wash off with a mixture of washing-up liquid and water. Treating the insects may involve pruning and destroying any heavily infected branches, spraying with a systemic insecticide or if the infestation is only light rub off the insects by hand.
Vine weevil beetles produce half-moon shaped cut-outs around the edges of the leaves and lay their eggs at the base of the stem. These eggs become larvae which then migrate into the soil and feed off the plant roots. The larvae are creamy white curled into a C – shape with a brown head. Eventually they will eat sufficient roots to kill the plant. Spray the foliage with a systemic insecticide at 2 – 3 week intervals to kill the adult beetles; also spray around the base of the plant as this is where the adult rests. Drench the soil around the base of the plant to control the larvae.
Viburnum opulus (Guelder Rose)
Recommended varieties
Viburnum opulus (Guelder Rose) – this is the wild, deciduous variety and can grow to 5m (16.5’). It has small white flowers in spring and clusters of red berries in the autumn. The leaves also turn red/pink in the autumn. It is a good tree for a mixed native hedge, giving good autumn colour and an important food source for the birds.
V. opulus ‘Xanthocarpum’ - yellow berried Guelder Rose with creamy white flowers. Leaves turn yellow or pink in autumn.
V. opulus ‘Roseum’ - large, deciduous shrub with creamy white flowers in a snowball shape. In autumn the leaves are a reddish colour but as the shrub is sterile it does not produce any berries.
V. davidii - small, spreading evergreen with white flowers and blue/black berries with a metallic sheen.
V. plicatum f. tormentosum ‘Pink Beauty’ - medium, deciduous shrub with flat creamy white flowers which turn pink as they age. In autumn the foliage turns purplish and it produces red/black berries.
V. plicatum f. tormentosum ‘Mariesii’ (Wedding Cake Tree) - small, deciduous tree with tiered branches. It has lacecap heads of white flowers in spring. It sometimes produces red berries which then turn black.
V. plicatum f. plicatum ‘Grandiflorum’ (Japanese Snowball) - large, deciduous shrub (small tree, 2.5 – 4m; 8’ – 13’) producing large balls of white flowers which turn pink with age. They are sterile so don’t produce any berries. The leaves turn purplish red in autumn.
V. x burkwoodii - loose, evergreen shrub growing to 2.5m (8’) with glossy dark green leaves. In mid to late spring it produces very fragrant white or pale pink flowers.
V. tinus 'Lisa Rose' - medium (2 - 4m, 7' - 13'), evergreen with glossy leaves, pale pink flowers from November to May.
V. tinus ‘Gwenllian’ - medium, evergreen shrub with white flowers in winter emerging from red buds, producing metallic blue berries in autumn.
V. tinus ‘Eve Price’ - medium, evergreen shrub producing starry white flowers in winter from deep pink buds. Berries in autumn are deep metallic blue.
Viburnum tinus 'Eve Price'
V. x bodnantense ‘Dawn’ - large, deciduous, strong growing, upright shrub producing fragrant white and light pink flowers emerging from red buds, from autumn through to spring.
