The most common Double Knock Out rose colors are pink and red. These were the only two colors available as of 2010. The Radtko Knock Out rose is a double cherry-red variety with blooms that are up to 3.5 inches in diameter and the Radtkopink Knock Out rose is approximately the same size and has bright pink flowers.
Though they have additional petals, Double Knock Out roses have a more limited spectrum of colors than that of the Single Knock Out varieties. Single Knock Out roses are available in red, pink, coral, white and yellow. Both types of roses are vigorous bloomers, putting on blooms until the first hard frost. They are hardy in U.S. Department of Agriculture zones 5 to 10.
Knock Out and Double Knock Out roses are shrub roses that grow from 3 to 4 feet tall and wide. They are self-cleaning roses that do not require deadheading to bloom every 5 to 6 weeks. However, occasional deadheading can increase bloom production and the overall growth of the plant. The rose benefits from monthly fertilization, though it is not necessary. Removal of dead or diseased wood may be done at any time. Knock Out roses are resistant to most diseases.