Plants - Roses

Secrets of super-hardy roses

How can you tell if a rose will prove hardy in your garden?

There is considerable mystery in growing roses, perhaps nowhere more so than in Canada. Which plants will survive winter in our lowest hardiness zones? Sometimes roses I expect to be rock hardy in my moderate Zone 6 garden—as was the case with the sturdy shrub roses ‘Westerland' and ‘Lady Penzance'—turn up badly injured or dead in spring. Yet my supposedly less cold-reliable floribundas, ‘Nearly Wild' and ‘Sue Ryder', shrug off the worst winter conditions and are studded with red leaf buds every April. Although hope springs eternal in this gardener, clearly more specific factors such as my garden's microclimate and environmental circumstances are at work.

Most rose plants reach their established size by the fourth season after planting (and six to seven years after seedling germination), when they have grown a full scaffold of canes and are ready for prolific blossom production. Read it and weep, for how many beautiful roses have succumbed to winter injury in less time, and before we ever witnessed their full capability? The secret to those that survive lies in plant selection and breeding, and the accumulation of genetic cold-hardiness traits from their ancestors.

This makes a case for researching a rose's bloodline before going shopping. Selecting roses along bloodlines involves as much sleuthing through old records as charting your own family tree, but it leads to insight as to which roses have the cold-hardy genes to better withstand winter and come up full of buds in spring.

Among the hardiest European wild species are Rosa x alba, R. eglanteria, R. foetida, R. gallica, R. pim-pinellifolia (syn. R. spinosissima) and R. kordesii, contributing their genes to such charming roses as the early-blooming ‘Harison's Yellow' (also known as Yellow Rose of Texas, with R. foetida genes) and the Hybrid Spinosissima ‘Stanwell Perpetual', which carries fruit-scented blooms to the end of autumn (both hardy to Zone 3). The superior Asian species R. rugosa, from northern China and Japan, was introduced to Europe and North America in the 1860s and quickly influenced breeding programs, marking the beginning of modern rose cultivars.

R. rugosa brought a stronger cold-resistant gene to rose breeding, with many of its hybrids hardy to Zone 2, and was soon matched by the North American wild species R. acicularis and R. arkansana. These three key species, along with the European wild roses already in use, greatly influenced the breeding work of Wilhelm Kordes in Germany and Griffith J. Buck in Iowa (which has a climate similar to the Prairies) as well as the development of the Explorer and Parkland series of hardy shrub roses in Canada.

Tough old dears
Eighteenth-century European rose breeders began blending wild species and more tender roses in the development of classic antique cultivars with cold hardiness, many of which are still loved today. These include the white ‘Boule de Neige' and pale pink ‘Louise Odier' (Bourbon); red-striped pink Rosa mundi and deep pink apothecary's rose (Gallica); white-edged pink ‘Hebe's Lip' and medium pink ‘Ispahan' (Damask); white-eyed, deep pink ‘Mozart' and buff to apricot yellow ‘Buff Beauty' (Hybrid Musk); and multicoloured white, pink and red ‘Striped Moss' and velvety scarlet ‘Etna' (Moss). All are hardy to Zone 5.

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