Cornus

These plants provide colourful structure in winter and flowers in summer, says Miranda Kimberley.

Cornus alba 'Elegantissima' AGM - image: Floramedia
Cornus alba 'Elegantissima' AGM - image: Floramedia

There are a few plants that help us through the winter gloom and Cornus is one of them. With their vibrantly coloured stems they provide fantastic structure in winter gardens and also contrast with early bulbs, especially the pure white of snowdrops. Later in the year, the flowering dogwoods provide earlysummer interest with their large white bracts.

It is a large and varied genus, made up of 65 species of mainly deciduous shrubs and small trees. C. alba, C. sericea and C. sanguinea produce varieties of dogwoods with stems that range in colour from yellow to red and even black-purple. They also have brilliant autumn foliage and bear handsome fruits.

C. florida, C. kousa and C. nuttallii are the flowering dogwoods, producing incredible large white or pink bracts in early summer. They also provide excellent autumn colour. Other ornamentals in the genus include C. mas, the Cornelian cherry that produces small, brightyellow flowers along its bare branches in the spring.

Several species are grown for the tiered effect their branches produce, earning them the name "wedding cake trees". The most popular varieties are C. controversa 'Variegata' Award of Garden Merit (AGM) and the smaller C. alternifolia 'Argentea' AGM. Both have lovely delicate foliage with green centres and white or cream margins.

Cornus can be planted in a sunny position or in partial shade, but full sun gives the winter stems the best colour. The shrubby dogwoods including C. alba, C. sericea, C. sanguinea, C. controversa, C. alternifolia and C. mas are tolerant of a range of soil conditions.

The first three species, grown for their stem colour and their cultivars, can tolerate moist soil while the flowering dogwoods prefer a well drained, fertile, neutral to acid soil.

Most Cornus species can cope with temperatures down to -10 degsC and even -25 degsC, although a few including C. capitata cannot tolerate below -5 degsC so should not be risked in colder areas of the UK.

Plants grafted onto C. kousa var. chinensis AGM are said to be the most suited to our climate, being hardy and vigorous. C. florida and C. nuttallii tolerate low temperatures but need long, hot summers to flower well.

Cornus can be quite slow growing when young but their growth rate picks up. The coloured-stem dogwoods are best left to establish for a few years before the annual coppice, when plants are cut back to 5cm in spring to produce the new bright stem colour - this can be too much of a shock for young plants.

The flowering dogwoods need little pruning other than clearing a short trunk in the autumn or spring when young.

Cornus does not suffer from many pests and diseases, but Cornus anthracnose or honey fungus could be a problem. Anthracnose shows up as spots on the leaves in late spring. Affected branches should be pruned out and burnt.

What the specialists say

- Karan Junker, co-owner, Junker's Nursery, Somerset

"Cornus is an incredibly varied genus. Lots of people are familiar with those grown for winter stem colour, but the flowering dogwoods - for example, C. kousa - that have gorgeous showy bracts from mid-spring through the summer are less well known. Further diversity is found with species that flower on bare wood in February, such as C. mas as well as tiny ground cover plants such as C. canadensis.

"We grow a huge range of flowering dogwoods, but the cultivars of C. kousa are best adapted to the British climate. I particularly like C. kousa var. chinensis 'Wisley Queen' although the hybrid C. 'Norman Hadden' is beautiful too.

"I recommend always choosing a named cultivar. This will guarantee the plant's characteristics will have been selected for a particular reason. This is particularly important with species like C. kousa - a grafted named cultivar will flower much earlier in its life and usually be far more spectacular than a random seed-grown plant."

- Steve Dance, office manager, Burncoose Nurseries, Cornwall

"Cornus is a wonderful group of plants, offering a range of specimens with beautiful flowers from spring to summer, as well as the vibrant coloured-stemmed varieties that can be used to lift the winter gloom.

"My favorite is C. 'Eddie's White Wonder' AGM. It can be virtually guaranteed to put on a brilliant display of flowers and good autumn colour. My tips for cultivation are to give the plants plenty of well-rotted compost or manure. They also do best sheltered from cold winds."

In practice

- Jonathan Webster, curator, RHS Garden Rosemoor, Devon

"We have two main types of Cornus in our collection. First are the flowering dogwoods such as C. kousa from Japan. These are shrubs of various sizes and shapes and some form reasonable sized trees. They are free from pests and diseases because they come from a climate similar to ours. They have many good attributes throughout the year, from stunning flowers during the early summer followed by strawberry-like fruit to dazzling autumn colour.

"The stem dogwoods are grown for their colourful winter and spring displays. These are mainly C. alba and C. sericea cultivars, which we use in various situations around our water features and in our themed winter garden. A tip is to let them establish for a couple of years before you start your annual coppice. This gives the plant time to establish. The annual cutback helps you to maintain the vivid and strong stem colours.

"Both groups of plants like our acid loam soil, which as you would expect is not short of moisture. We plant them around the garden but the kousas are better in a woodland situation and the stem dogwoods traditionally look great around water.

"Establishment with us is not a problem. Some people suggest not planting the kousas in midwinter if they are grafted forms because failure can occur."

Species and varieties

Dogwoods with colourful stems

- C. alba 'Aurea' AGM (H4) has red stems and bears greenish-yellow leaves that turn a golden colour in the autumn.

- C. alba 'Elegantissima' AGM (H4)features variegated leaves with an olive-green centre and creamy margins. The leaves drop in late autumn to show off the red stems.

- C. alba 'Kesselringii' has brownish-black stems and green foliage that turns a deep violet in autumn.

- C. alba 'Sibirica' AGM (H4) has flame-coloured foliage in autumn and bright-red stems that stand out in the winter. Height and spread: 3m.

- C. alba 'Spaethii' AGM (H4) is grown for its brilliant red winter stems and foliage that is pale-green edged with broad, irregular yellow margins. Also bears creamy-white flowers from May to June. Height: 2.4m. Spread: 3m.

- C. sanguinea 'Midwinter Fire' has young stems that are a brilliant orange-yellow from autumn through to spring, with red tints on the sunnier sides of the stems. The stems turn a yellow-green when the new leaves appear. They are bright-green, turning a brilliant yellow in autumn.

- C. sericea 'Flaveiramea' AGM (H4) (syn. C. stolonifera 'Flaviramea') produces yellow-green stems in winter. It also bears clusters of white flowers in May and June and oval, dark-green leaves that redden in autumn. Height: 1m. Spread: 1.5m.

Flowering dogwoods

- C. alternifolia 'Argentea' AGM (H4) becomes a large shrub or small tree with a handsome tiered shape at maturity, earning it the common name the variegated American wedding cake tree. Its cream and green leaves give it a graceful look and in summer it bears clusters of white flowers. A slow-growing plant, so buy a mature one to get the effect quicker. Height: 3m. Spread: 2.5m.

- C. controversa 'Variegata' AGM (H4) is a small tree with green and cream variegated leaves and distinct tiers of branches once established, leading to it being known as the wedding cake tree. It is a larger tree and has larger leaves than C. alternifolia 'Argentea' AGM (H4). Height: 10m. Spread: 6m.

- C. 'Eddie's White Wonder' AGM (H4) is a popular cultivar that reliably produces attractive large white flower bracts in late spring. The ovate leaves turn red and purple in autumn. Height: 4-8m. Spread: 2.5-4m.

- C. florida is a small tree or spreading shrub with white bracts from the eastern USA. This species flowers between C. nuttallii and C. kousa. It can be susceptible to anthracnose so go for grafted options or disease-resistant varieties such as the 'Cherokee' group. Height: 10m.

- C. kousa is a broadly conical, deciduous tree that produces white bracts and large, wavy-margined, dark-green leaves that turn a deep crimson-purple in autumn. The flowers are followed by strawberry-like fleshy red fruits. Many popular varieties have been bred form this species, including 'China Girl' and 'Miss Satomi' AGM (H4).

- C. kousa var. chinensis AGM (H4) is a stunning large shrub or small tree. It differs from the species in that is has smooth margined leaves and large tapered bracts that open creamy-white, turn white and end red-pink. The foliage turns red and orange in the autumn. Height: 8m. Spread: 5m.

- C. mas or the Cornelian cherry is deciduous shrub or small tree with a spreading habit. In early spring it produces small bright-yellow flowers along the naked stems. The foliage turns reddish-purple in autumn and it bears bright-red, cherry-like edible fruits. Height and spread: 5m.

- C. nuttallii can reach 30m in its native western America but UK cultivars are more likely to reach only 5m. Produces excellent hybrids with C. florida, with spectacular flower bracts that are greeny-white to cream, sometimes developing a pink flush.

Thank you to Floramedia, which supplied the images for this article from its photo library

www.floramedia-picture-library.com


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