Knock Out roses first appeared on the market in 2000, after being named an All America Rose Selection. These hardy, heat-tolerant shrubs are the most widely sold rose in North America, according to Conard-Pyle Co. Single Knock Outs come in red, pink, coral, white and yellow, but doubles come only in red and pink, as of 2010. Knock Out roses bloom continuously until the first hard frost, and they thrive in USDA zones 5 to 10.
The 'Radtko' Knock Out rose has cherry-red double blooms with 18 to 25 petals each. The blooms are 3 to 3 1/2 inches in diameter, with a slightly spicy, tea-rose fragrance. Each cluster has up to five flowers, with as many as 25 blooms per branch. The plant is compact, growing as a mounded shrub 3 to 4 feet high and wide. Its foliage is deep moss green with a maroon underside.
The 'Radtkopink' Knock Out rose comes with bubble-gum pink double blooms. The blooms have 18 to 24 petals, and they grow 3 to 3 1/2 inches in diameter. Their scent is a slightly spicy tea rose. Each cluster has up to five flowers, with as many as 25 blooms per branch. The compact, mounded shrub grows to 3 or 4 feet high and wide, and it has deep green foliage that turns deep purple in the fall.
Growing Knock Out roses is extremely easy. The blooms do not require deadheading in order for the shrub to flower again. Fertilization can be done once a month, but is not necessary. Pruning involves only shaping the bushes to the size you prefer and removing dead or diseased wood. Knock Out roses should not be allowed to dry out between waterings. All varieties are resistant to common rose diseases.