Knockout® roses, developed by a landscape architect from Milwaukee by the name of William “Bill” Radler, were introduced in 2000, and have continued to be popular with professionals and home gardeners. A hybrid of the Carefree Beauty and Razzle Dazzle seedlings, the first Knockout® rose introduced on the market was the Rosa ‘radrazz”. Since that time, there are over seven varieties available. It is rumored that Radler is cultivating several more to be introduced in the near future.
Knockout® roses require a minimum of six to eight hours of exposure to sunlight daily as well as well-drained soil with a pH between 6.0 and 6.5 to grow to their documented heights of 3 to 5 feet. Prized for their minimal need for human intervention to bloom and flourish, the Knockout® rose is known to be drought tolerant, self-cleaning, and resistant to black spot and powdery mildew. However; there have been reports that the rose has developed a vulnerability to the Rose Rosetta Disease (RDD).
The typical manifestations of RDD include a red pigmentation of the underside of leaf veins followed by sharply increased growth of vegetative shoots also colored red. Transmitted by an eriophyid mite there is no known remedy for the disease other than to remove the infected plant material in its entirety.