The original Knock Out rose (Rosa "Radrazz") was bred by Bill Radler in 2000 and has since become the best-selling rose in the United States, according to Conard-Pyle, the company that introduced the rose. Although Knock Out roses are less fragrant than other roses, they are disease-resistant, drought tolerant when established, and hardy to U.S. Department of Agriculture plant hardiness zones 5 through 9. Knock Out roses are fast growers that require minimal care.
Description of Knock Out Roses
Knock Out roses are classified as shrub roses. Typically, Knock Outs grow 3 to 4 feet in height and width, but they can reach 6 feet tall and wide if not trimmed. The original Knock Out rose (Rosa "Radrazz") has single-petaled, cherry-red flowers. Many varietals have been introduced since the creation of the Knock Out with bloom colors from pink to yellow. The Double Knock Out (Rosa "Radtko") has full double flowers that closely resemble classic roses.
Roses should receive at least six to eight hours of sun each day. Although Knock Out roses are resistant to powdery mildew and black spot, they do best with good air circulation. Plant them with at least 1 foot of space between their mature size. Knock Out roses do best with well-drained soil with a pH between 6.0 and 6.5 and a thin layer of mulch -- about 3 inches -- that retains water. Water regularly while the roses become established, after which they don't require much care.
After the rose is established, Knock Outs can grow 2 to 3 feet in one spring growing season. Depending on which season you plant, the height of your 1-gallon plant at purchase and the establishment of the roots, it may take one to two years to reach full mature height.
In early spring, use lopping shears or hedge trimmers to cut back the Knock Out rose by two-thirds of the plant size. The plant will regrow to 3 to 4 feet by the end of the growing season. Knock Out roses are self-cleaning, so there's no need to deadhead spent blossoms.
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