Cornus are the dogwoods, some of which are grown primarily for their coloured, some for their ornamental and some for their , or the showy, petal-like bracts that surround the true flowers. Since these different effects entail different treatment in the garden the need to be treated separately.
The dogwoods with colouredor variegated leaves all thrive in most soils and places, including those that are very wet. The best bark effects are produced by all stems back to within a few inches of the base in early spring and the same treatment can be given to the foliage varieties or they can simply be thinned out a little, some of the older stems being removed where overcrowded. Cornus alba sibirica, the Westonbirt dogwood, has crimson stems and C. stolonifera flaviramea has greenish-yellow stems. C. alba elegantissima has white-variegated leaves and C. alba spaethii, yellow-variegated leaves.
The best dogwood to grow for true flowers is Cornus mas, the Cornelian cherry, a tall, loosely branched shrub with clusters of small yellow flowers in February, but more spectacular are the bract-bearing kinds such as C. kousa with big white bracts in June, and C. florida rubra with pink bracts in May. Both make big bushes or small, widely branched trees and do best in good, loamy soil, preferably moderately acid and without lime or chalk. They need no.
Those members of this genus which reach the proportion of small or medium-sized trees are most desirable and ornamental, contributing both striking floral and autumn-colouring effects. The flowers are conspicuous by reason of white or coloured bracts or modified leaves which surround the true flower clusters. The cornels or dogwoods will grow on most soils but several species make poor growth in shallow chalky conditions.
Cornus capitata (Benthamia fragifera) is an evergreen Himalayan species making a small bushy tree often wider than high. Its leaves are up to 5 in. long, grey green and downy making a pleasing background for the mid-summer ‘flowers’ which comprise four to six large pale yellow bracts surrounding the remaining flower parts. Equally conspicuous in the autumn are the large, strawberry-shaped, crimson fruits. Regrettably this handsome tree is only successful in the mildest coastal districts of south and west England and similar climates.
A fine and architecturally significant Japanese species, C. contraversa eventually makes a medium-sized tree with tiers of horizontal branches. These are arrayed at mid-summer with clusters of cream-coloured bracts. On most soils the leaves turn purple in the autumn.
The flowering dogwood, C. florickz, form a small tree, often with a widespreading head conspicuous in late spring when it displays masses of white petal-like bracts. This is also one of the trees responsible for the spectacular fall colour of the eastern U.S.A. Where it is native. After a hot summer, the leaves colour well in the British Isles but it is generally less happy here thriving best in east or south-east England in sites free from spring or early autumn frosts. This species is rather intolerant of chalk soils. There are a number of varieties selected on account of the exceptional colour of their flower bracts. The variety rubra is rose red; Cherokee Chief is a deeper rose red, an American selection, and White Cloud, another American selected form, has brilliant white bracts freely borne.
C. kousa chinensis is a geographical form of the Japanese C. kousa and a most beautiful hardy small flowering tree. It produces its large long-lasting white bracts at mid-summer followed by round red edible fruits. The leaves, also larger than in the type, colour well for a long period in autumn. It is less successful on chalky soils.
The Pacific dogwood, C. nuttallii, is the doyen of the cornels, a native of western North America where it attains a height of 50 ft. or more. The large white bracts open in late spring. Regrettably it tends to be short lived in Great Britain but it is often seen as an upright shrubby small tree spectacular in flower from the ground to its summit. It is not suitable for chalk soils.
C. alba (syn. C. tatarica), red-barked dogwood, is a fully hardy shrub, 3-4 m tall, which flowers from April-May/June. It has erect, reddish-brown shoots, broad, elliptical, green leaves, bluish-green on the underside, creamy-white flowers up to 3.5 cm across, and white or bluish-white fruits; ‘Elegantissima’ (syn. Argenteomarginata) has deep red shoots and pale green leaves with a creamy margin; ‘Sibirica’, up to 1.5 m tall, is smaller and has bright red stems.
C. alternifolia grows vigorously in stages and flowers from May-June. It has brownish-red stems, spreading leaves, clusters of small, white flowers and dark blue fruits; ‘Argentea’ has white, variegated leaves.
C. canadensis, creeping dogwood, is suitable for ground-cover, 10-20 cm tall and flowers from June-July. It has creeping stems, erect stalks, rosettes of shiny green leaves, green flowerheads with white bracts, and compact, orangey-red clusters of edible berries. It tolerates shade and slightly acid soil.
C. contraversa is a winter-hardy tree, 3-10 m tall, with an erect trunk and layered branches. It flowers from June-July, has slightly pendent, greyish-brown branches, spreading, oval, dark green leaves up to 12 cm long, creamy clusters of flowers and dark blue fruits (occasionally); ‘Variegata’ has green leaves with a broad, white edge; suitable as a specimen tree.
C. florida, flowering dogwood, 4-5 (-10) m tall, 2-4 m broad. It flowers in May, just before the leaves come out, and has reddish-brown branches, elliptical to oval leaves which turn orange to purplish-red in autumn, yellow flowers surrounded by four white bracts, up to 10 cm long, and compact clusters of red berries; ‘Rubra’ has pink-coloured bracts; suitable for acid soil.
C. kousa is 4-6 m tall and approximately 3 m broad. It is a spreading tree or shrub which flowers in May-June and has oval, shiny, dark green leaves, greyish-green on the underside, turning scarlet in autumn, large, creamy-white, red-tipped bracts, and red, strawberry-like fruits. Not suitable in clay soil; beautiful as a specimen plant.