According to horticulture experts at Louisiana State University, Knock Out Rose bushes have been a popular choice with gardeners all over the United States since their introduction to the market in 2000. This repeat bloomer always outperforms traditional roses in the area of disease resistance, requires very little maintenance and provides consistent color from spring until frost.
Choose a location where your Knock Out Rose bush will receive at least six to eight hours of sunlight per day. Dig a hole at least twice as wide and deep as your container, and enrich the soil by adding organic matter, such as shredded leaves, manure or potting soil.
When you place your rose plant in the hole, check to see that the bud union, or the knobby part at the base of the stem, is at the proper level. In hardiness zones 6 to 10, it should be about 1 inch above the soil line. In zones 5 or lower, your Knock Out Rose will benefit from burying the bud union about 1 inch below the soil. Backfill the hole, adding more soil if needed. Water the plant thoroughly, and mulch.
One of the greatest attributes of Knock Out Roses are their natural resistance to disease. Most knockouts don't require any type of spraying or maintenance for the usual rose problems like black spot or powdery mildew.
Deadheading Knock Out Roses is not necessary. Your plant will shed its old blooms and repeat the show every five to six weeks from spring until frost. All that is needed to maintain your rose bush is a yearly pruning in the spring (make sure the last hard frost is behind you) to about one-third or one-half its height. This promotes vigorous growth and blooming. Some pruning may be repeated during the growing season to maintain your rose in the appropriate size for its location.
Pros and Cons
With all the positive characteristics to recommend the Knock Out Rose to gardeners, is has a couple of drawbacks old-fashioned roses don't have. Most Knock Outs don't emit the lush fragrance typical of their older cousins. Instead, they have a much lighter, tea-rose fragrance. Additionally, they don't perform very well as cut flowers.
Knock Out Rose bushes come in standard and "double" varieties. The Double Knock Out has dense, double blooms that more closely resemble old-fashioned roses. There are red, pink and coral selections in the Knock Out family, along with the newest offering, the "Sunny" Knock Out rose. This variety offers yellow blooms against dark-green foliage and a more intense fragrance than other members of the Knock Out breed.