Initial Recommendations from the Maine and Vermont Field Trials
Roses in northern New England face many challenges, including long, cold winters that often kill hybrid roses. Shrub roses offer an excellent alternative to hybrid teas, grandifloras and floribundas. But which ones are reliably hardy?
In 1997, we initiated field trials to address the question of shrub rose hardiness at two sites: the University of Vermont's Horticulture Research Center, South Burlington VT (USDA Hardiness Zone 4B), and the University of Maine's sustainable agriculture research facility, Rogers Farm, Stillwater ME (USDA Hardiness Zone 5A).
We obtained roses from commercial sources, planting one plant each of many species and cultivars, with considerable overlap of cultivars at the two sites. We add more roses each spring, and the plantings now contain over 130 cultivars at each site. At both sites, roses are spring-planted, mulched, fertilized, and watered as needed. At the Stillwater ME site, roses are top-mulched with 12" sifted compost in November of their first season, but not winter-mulched in subsequent years.
Each year in early summer, all roses at each site are rated for winter survival, on a scale from 1 (dead) to 5 (excellent growth). A rose rated "5" for several years would perform well in a low maintenance landscape. A rose rated "3" for several years would be appropriate for a northern New England landscape where spring pruning is an accepted labor practice.
Based on 3 years of hardiness ratings at each site (1998-2000 in Burlington VT and 1999-2001 in Stillwater ME), we've selected shrub roses that seem to perform well in northern New England conditions. These have been updated with average survival rates measured through 2005.
Shrub Roses for Northern New England:
Alba Roses: free-branching shrub roses with relatively few thorns; semi-double to double, highly fragrant flowers in clusters of 5-7 in June; flowers produced on shoots from second year wood.
ˇ Rosa 'Alba Maxima' also called 'The Jacobite Rose' (3.9)
ˇ Rosa 'Félicité Parmentier' (3.8)
ˇ Rosa 'Königen von Dänemark' (3.9)
Gallica Roses: dense, free-branching, and generally prickly; single to fully double roses, most of them scented, from spring to early summer; pink, red or maroon flowers produced on shoots from second-year wood.
ˇ Rosa 'Rosa Mundi' (3.5)
ˇ Rosa 'Charles de Mills' (3.8)
Explorer Roses: modern roses developed by Agriculture Canada based on the hardiness of Rosa kordesii.
ˇ Rosa 'John Davis' (3.8)
ˇ Rosa 'John Cabot' (3.8)
Moss Roses: lax, thorny shrubs; white, pink or red flowers in clusters of 3 or more; generally fragrant and semi-to fully double.
ˇ Rosa 'Henry Martin' (3.6)
Shrub Roses: rather artificial group of roses that don't easily fit into other categories; most flower in early summer; wide range of traits, including hardiness.
ˇ Rosa 'Prairie Dawn' (3.4)
Species Roses: naturally occurring roses with little or no improvement from breeding efforts.
ˇ Rosa eglanteria 'Magnifica' (4.5)
ˇ Rosa acicularis (4.5)