The original Knock Out rose (Rosa hybrid "Radrazz") revolutionized landscape shrub roses by taking low maintenance, disease resistance and near-constant blooming to new levels. Double Knock Out (Rosa hybrid "Radtko"), hardy like its predecessor in U.S. Department of Agriculture plant hardiness zones 5 through 11, offers all those benefits, plus fully double flowers. Understanding the characteristics of the Double Knock Out rose can help maximize your enjoyment of its blooms, whether in your garden or in a vase.
Knock Out debuted in 2000 as an All-American Rose Selection. According to Conard-Pyle Co., which introduced the rose, it became the best-selling new rose of all time, and remains North America's most widely sold rose. Double Knock Out was bred from the same parents as the original. Both were developed specifically for landscape performance rather than as cutting flowers. These roses exhibit shorter stems and plentiful branching for a dense, full, landscape plant, and bear clustered flowers with long-staying bloom power. Double Knock Out can add elegance to a bouquet, but they lack the long, single stems and extended vase life of roses grown especially for that purpose.
Double Knock Out offers fully double blooms. Each pointed bud carries 18 to 24 cherry-red petals that open to blossoms measuring 3 to 3.5 inches across. Stems 8 to 12 inches long bear clusters of one to five flowers, with up to 25 blooms per flowering branch. A vigorous grower, Double Knock Out forms a dense, compact shrub 3 to 4 feet high and wide. Maroon highlights and maroon undersides on the moss-green leaves complement the blooms. In fall, the foliage takes on a deep-purplish cast, and the maroon undertones deepen as well. Double Knock Out flowers continuously from late spring to frost; in warmer winter climates, it will flower all year round.
As a cut flower, Double Knock Out lasts only a few days, but you can take steps to prolong its vase life. Cut your roses in early morning before the heat of the day. Buds that are not fully tight, but not yet open will last the longest. Carry a container with water into the garden, and put the blooms in water immediately when you cut them. Short, full, informal arrangements will work best with these roses. Use the rims of your vase and the foliage of other flowers to provide support and help the stems stay open for water. Floral preservative and a cool spot away from direct sunlight will also extend their beauty.
The care you give your Double Knock Out shrub will keep the supply of flowers coming. Plant it in well-drained soil where it will receive six to eight hours of daily sun and good air movement. The Double Knock Out is extremely disease-resistant, and it adapts to a wide range of soil pH. Water the plant regularly until it's well established. Apply mulch to help conserve soil moisture, always keeping the mulch back from direct contact with the base of the rose. To promote maximum flowering, shear the plant back by two-thirds every spring. Double Knock Out drops its spent flowers, so removing them by hand is not necessary, but doing so can speed the next cycle of flowers.