Pruning promotes strong growth and flowering. It also helps keep Knock Out roses a manageable size as in ideal conditions they can easily grow 6 ft high and 6 feet wide or more.
Knock Out roses, like other everblooming roses should be pruned two times a year. Best time to prune in the spring is at the end of the dormant season. This can vary depending on your climate. It is recommended that spring pruning reduce the height of the bush by one-half to one-third, or one to two feet shorter than you want them to be in the summer.
During the summer flowers can be deadheaded if desired, but pruning is discouraged as the heat stresses the roses.
The second major pruning should take place in fall. This is not as severe as the first pruning and plants are generally cut back to about one-third of their height. It is recommended that plants be fertilized after this pruning.
When pruning, remove dead or damaged branches and branches that rub against larger branches as these all make the roses more susceptible to diseases. Old unproductive growth and branches that cross through the rose plant’s center can be removed as well to open up the center of the bush. Cuts should be made a quarter inch above a leaf bud and angled at the same angle as the bud. To avoid spreading diseases, it is a good idea to wipe off pruning tools with rubbing alcohol between plants.
Winter care for Knock Out roses depends greatly on climate. If you live in USDA zones 5 through 11, the only thing you need to do is place a thick layer of mulch around the base of your rose after the ground freezes. If you live in a colder climate you’ll want to cover the base of the rose with about 12 inches of soil with additional straw or leaves for insulation (or use a Styrofoam rose cone with soil mounded around the outer edge). This protection should remain in place until the buds break open in spring.
Rose Gardening Made Easy – How to Prune Knockout Roses
Rose Gardening Made Easy – When to Prune Knockout Roses
LSU Ag Center – Knock Out roses do require pruning
Grow Exquisite Roses – How Important is Deadheading Knockout Roses?
Clemson Ask A Master Gardener – Pruning Knockout Roses, When and How
P. Allen Smith – Knock Out Rose Winter Care