Tree of the month: A rose by any other name

INTEREST in Rosa canina (dog rose) for hedgerow and woodland-margin planting is rising. Dog rose is native, fast-growing and -colonising without being invasive. It is good for biodiversity, including pollinating insects, small mammals and birds.

One might hesitate to call dog rose a tree, and by placing ‘dog’ as a prefix in the name, our ancestors clearly believed it was not even worthy of the title of rose. ‘Dog’ as a prefix in plant names is historically derogatory, implying inferiority (in this case to English garden roses).

However, anyone about to run with the romantic notion that Rosa canina was fundamental to the evolution and development of English garden roses had better think again. In the same way that English apples have their roots in Central Asian wild Malus (apple) species, garden roses have their roots in Middle Eastern roses like the Damask rose (Rosa x damascena), the most fragrant of roses and itself a hybrid of Rosa gallica and Rosa moschata.

Known in William Shakespeare’s time as ‘eglantine’, what dog rose lacked in scent it made up for in blushing beauty. Indeed ‘English rose’ when used to describe a naturally attractive English woman or girl of traditionally fair complexion was almost certainly likening the lady to ‘Rosa canina’. However, caution may be advised, because ‘eglantine’ was also used to describe Rosa rubiginosa (sweet briar).

The name ‘dog’ may well sound disparaging, but Rosa canina has ‘teeth’ in its razor sharp and typically curved thorns, spread along the wayward stems.

Dog rose bursting into bloom in June is a sure sign that summer has well and truly arrived.

NATURAL DISTRIBUTION

Rosa canina is a variable climbing species native to Europe, north-west Africa and western Asia. It is widely distributed throughout the British Isles, though generally more common in southern and central England, Wales and Ireland, albeit less now than before WWII, due the widespread destruction of hedgerows.

It is a deciduous shrub ranging in height from 1 to 5 m, though sometimes scrambling higher into the crowns of taller shrubs and trees which provide support. Stems are erect to arching, 3 to 5 m long, more or less hairless but with vicious thorns. The thorns, which aid the plant’s climbing, are 5 to 6 mm long, flattened with a broad base and generally hooked. Those on the main shoot are often borne in pairs (whorled) and usually sparse, but on branches thorns are smaller and more abundant. Bark is green or red-brown, becoming grey with age. Clearly there is little material for craftsmen to play with, but the old hard wood has been used to make chess pieces.

Leaves are borne alternately on a prickly petiole (leaf stalk) compound pinnate in form with five to seven leaflets, oval to elliptic in shape with pointed tips, rounded bases, and are glandless or with glandular hairs.

Dog rose flowers appear during June and July in clusters of up to four at the ends of the stems and are typically 4 to 6 cm in diameter. Flower stalks are hairless, smooth and 10 to 15 mm long. Five sepals at 10 to 25 mm in length are longer than the receptacle, lance-shaped or pinnately lobed at the top of the floral tube. Some may bend back post flowering and can remain attached to the fruit for some time. Sepals are without hairs or prickles.

Five petals are 12 to 21 mm long and attached to the edge of the floral tube. Petals are most frequently pastel pink but can vary from white to a brighter, darker pink. Yellow-coloured stamens (male parts) are many, of varying length and attached to the edge of the floral tube. Carpels (female reproductive parts) become achenes.

Fleshy fruits, commonly called hips, are dark red to bright orange-red in colour when ripe, egg-shaped to globular, 10 to 26 mm long by 9 to 12 mm in diameter, weighing in at 1.7 to 3.2 g, fleshy when ripe and softening with successive frosts. Rosehips are smooth and shiny and contain around 16 seeds. Sepals are deciduous but often remain attached to the fruit for some time. Rosehips are exceptionally rich in Vitamin C (ascorbic acid). As part of the self-sufficiency programme during WWII, huge volumes were collected in the countryside to make rosehip syrup. Rosa canina was cultivated as a medicinal plant in 12th- and 13th-century Russia.

Seeds are yellowish, many in number, small (up to 6 mm long) and irregularly angled. Dog rose is usually cross-pollinated by insects, but in some cases flowers do self-pollinate. Dog rose seed may germinate at any time of year, though the big flushes naturally occur in spring and autumn, which is the best time to germinate the seed. They contain a chemical compound called alpha pyrone with allelopathic properties, which means it can inhibit germination of other seeds.

Scented flowers of the dog rose are highly attractive to pollinating insects.

NURSERIES AND PLANTING

Dog rose is widely available from nurseries as a relatively cheap, sun-loving shrub for hedgerow and woodland-edge planting. This species will grow virtually anywhere, except in waterlogged ground, and does especially well on chalky soils and near the sea. Dog rose is an ideal plant for generating dense and secure hedgerows up to around 3 m in height and is even better when in a mixed planting with Crataegus (hawthorn). As stand-alone shrubs, dog rose rarely exceeds 1.5 m in height, but when alongside taller-growing shrubs and trees it will scramble up and easily reach 3 m. After 10 years, bushes will typically attain a 1.5 m by 1.5 m size.

Mid October, and already red-ripe, rosehips are beginning to soften up to provide vital winter food supplies for a range of birds and small mammals.

ECOLOGICAL ADVANTAGES

Dog rose provides colour and cheer through the year, with delicate pink/white flowers during early summer and orange-red hips during autumn and winter. Along with common elder blossom, the first flowers of dog rose are the sign of spring graduating into summer.

Dog rose delivers wildlife value, with insects attracted to the flowers and birds feeding on the fleshy hips, as do many small mammals, including bank voles and wood mice. Smaller birds eat the seed inside. Larvae of lepidopteran insects (butterflies and moths), including the common emerald (Hemithea aestivaria) and vapourer or rusty tussock moth (Orgyia antiqua), feed on the foliage.

Rosehips start to colour up in September.

INVASIVE TENDENCIES

Rosa canina can get out of control in parts of the world outside of its native range and distribution.

Early European migrants introduced dog rose into North America where it can now be found growing down the east and west coasts. Dog rose in North America is classed as extremely invasive and, once established, is very difficult to control.