Response of Selected Landscape Roses to Low-input Cultural Practices, High Disease Pressure, and Severe Heat and Drought Conditions

The major purpose of this five-year Earth-Kind^® research study was to document the responses of 100 cultivars of landscape roses to low-input cultural practices and heavy black spot disease pressure, followed by severe heat and drought conditions.  Cultivars, over half of which are winter hardy to at least Zone 5, were chosen based on their reputations of being strong performers in low maintenance landscapes and represent a range of floral characteristics, release dates, and plant habits. Planted in moderately alkaline, calcareous clay soils in a public park in Farmers Branch, Texas, a suburb of Dallas, these roses received no soil amendments, no fertilizer, no pesticides of any kind, no removal of spent blooms, and almost no pruning.  A three-inch-thick mulch of raw wood chips mixed with tree leaves was applied to the soil surface and maintained at this thickness throughout the study.  During the fourth year of the study, the plants were subjected to an 89.3% reduction in supplemental irrigation during the worst drought in this area in the past 75 years.  Landscape performance, including disease tolerance, was exceptional for approximately 20% of the cultivars.  Many of the cultivars have equaled or exceeded the mature height and width dimensions listed in reference sources. Some cultivars were resistant to black spot, whereas other cultivars were heavily infected with this disease. Only a few cultivars displayed significant levels of powdery mildew, Alternaria petal blight, or Cercospora leaf spot. Reaction to severe, prolonged heat (up to 110 °F) and drought conditions (12 month duration) were mixed: approximately 10% of the cultivars were severely impacted, 50% of the cultivars showed significant drought stress, and the remaining 40% exhibited only minor symptoms of foliar drought stress.  The plants received supplemental irrigation only three times during this very stressful 12-month period.  Results of this study identified multiple rose cultivars suitable for growing in low-input landscapes consistent with the Earth-Kind management strategy.