Knock Out rose trees originated in 2000 when rose breeder Bill Radler engineered a rose designed to be both self cleaning and disease resistant. All types of Knock Out rose automatically remove spent flowers, reducing the need for gardeners to trim dead roses or deadhead. These low-maintenance roses need only light pruning unless gardeners want to keep them below their maximum size of 3 to 4 feet in height and width.
Check your Knock Out rose tree, looking for dead or damaged canes. While this rose bush should not get diseased canes, rose branches can break under the load of winter snow or ice; periodically canes die as they age. Damaged canes appear bent; dead ones turn light tan in color and feel hollow.
Clip off damaged, broken or dead canes at their base to clean up your Knock Out Rose.
Prune the entire Knock Out rose tree back by one-third to one-half. Use hedge clippers to trim back the rose tree. Clipping back your Knock Out rose controls the plant's size and promotes the growth of new flowering wood. Knock Out rose manufacturer Conard Pyle notes that this may leave rose trees only 12 to 18 inches above the ground, but this is fine. The rose will regrow and thrive.