Landscape roses (Rosa sp.) are popular flowering shrubs. Consumers are less willing or able to maintain landscape beds than in years past and require plants that are not only attractive, but well-adapted to regional climatic conditions, soil types, and disease and pest pressures. Marketing and distribution of rose cultivars occurs on a national level; therefore, it is difficult for U.S. consumers in the U.S. Department of Agriculture (USDA) Plant Hardiness Zones 3 to 5 to identify welladapted, cold-hardy cultivars. Identifying suitable cultivars that have strong genetic resistance to pests and disease and that will tolerate temperature extremes without winter protection in the USDA Plant Hardiness Zones 3 to 5 is of tremendous value to consumers and retailers in northern states. Twenty landscape rose cultivars, primarily developed in north-central North America, were evaluated at five locations in the United States (three in the north-central United States, one in the central United States, and one in the south-central United States) using the lowinput, multiyear Earth-Kind® methodology. Six roses had ≥75% plant survival at the end of the study and were in the top 50% of performers for overall mean horticultural rating at each of the three north-central U.S. sites: ‘Lena’, ‘Frontenac’, ‘Ole’, ‘Polar Joy’, ‘Sunrise Sunset’, and ‘Sven’. Five of these six roses met the same criteria at the central United States (exception ‘Lena’) and the south-central United States (exception ‘Polar Joy’) sites. Cultivar, rating time, and their interaction were highly significant, and block effects were not significant for horticultural rating for all single-site analyses of variance. Significant positive correlations were found between sites for flower number, flower diameter, and overall horticultural rating. Significant negative correlations were found between flower number and diameter within each site and also between black spot (Diplocarpon rosae) lesion size from a previous study and overall horticultural rating for three of the five sites. Cane survival ratings were not significantly correlated with overall horticultural rating, suggesting some cultivars can experience severe winter cane dieback, yet recover and perform well. Data from this study benefit multiple stakeholders, including nurseries, landscapers, and consumers, with evidence-based regional cultivar recommendations and breeders desiring to identify regionally adapted parents.
Bibliographical noteFunding Information:
We thank the many generous volunteers (e.g., Master Gardeners and rose society members) that helped make this research possible. There were three additional trial sites in Bellevue, NE (led by Kathleen Cue, Anita Eckley, and Joanne Langabee), Fort Collins, CO (led by Tamla Blunt), and Crookston, MN (led by Eric Castle) that were planted and established, but unfortunately lost due to flooding or wildlife before complete sets of data were collected. We wish to acknowledge Linda Farris for plot maintenance and all data collection at the Haysville, KS location. In addition, we acknowledge and thank: Bailey Nurseries Inc., Bergeson Nursery, Star® Roses and Plants, Greenheart Farms, Inc., Holland’s Landscaping and Garden Center, and Sam Kedem Nursery & Garden for their generous donations of roses for this trial; Christian A. Thill and Jeffrey Gillman at the University of Minnesota for use of facilities to hold plant material until distribution; and Arunendu Chatterjee for his assistance with statistical analyses. We also thank: the city of Moorhead, MN, for supplying land, compost, and mulch for the trials and preparing the land for planting, the Northwest Regional Sustainable Development Partnership for a grant to support the Moorhead, MN site, the University of Minnesota Outreach, Research, and Education Park for land for the trial and site preparation, The Mulch Store for their donation of compost at the Rosemount, MN site, and the Greater Milwaukee Rose Society for the financial support that covered the publication costs of this research.
- Black spot
- Cane survival
- Rosa hybrida
- Shrub roses