Knock Out roses are disease-resistant, long-blooming landscape shrub roses.
Roses are not only beautiful landscape shrubs, but also useful for cosmetics, cooking and healing. Yet many classic varieties are notoriously prone to disease, requiring time-consuming care regimens. Researchers at Texas A&M University recently reported on a three-year trial of 116 different rose cultivars grown with minimal care in hot, humid north-central Texas—where black spot and other rose diseases are rampant.
The researchers evaluated the most highly recommended roses (based on input from rose enthusiasts and nursery professionals), from antique and old garden roses to the newest shrub roses in the most challenging conditions: no fertilizer, pesticides, deadheading or pruning, and minimal watering. The roses were subjected to alkaline, clay soil, heat, drought and high humidity. Cultivars were later evaluated for overall performance, bloom coverage and vigor.
Of the 116 cultivars tested, the top five overall performers were (in order) Knock Out (RADrazz), Caldwell Pink, Sea Foam, Perle d’Or and The Fairy. The worst were Trumpeter (MACtrum), Westerland (KORlawe), Marechal Niel, Paul Neyron and Baronne Prevost. Of the eight classes evaluated, Polyantha roses fared the best, with the highest overall survival rate, best vigor and most blooms. Hybrid tea roses performed the worst.
Although roses can perform differently in various regions and conditions, this long-term study supports other trial results in which Knock Out roses have performed well. Knock Out roses are disease-resistant, long-blooming landscape shrub roses hardy to Zone 5; they are widely available at retail garden centers.
For more information, see HortTechnology July-September 2008
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