For every gardener who's ever pampered a hybrid tea rose (Rosa spp.), only to gather a rose or two before the plant succumbed to black spot or some other malady, Knock Out roses (Rosa "Radrazz" Knock Out) might seem heaven-sent. But these sturdy roses are not entirely maintenance-free. Like other roses, they benefit from enlightened pruning. In the Knock Outs' case, pruning is best accomplished in early spring.
The Knock Out Idea
Kock Out roses are a group of shrub rose varieties developed by Milwaukee rosarian William Radler, beginning with “Radrazz” in 2000. Knock Outs are exceptionally hardy, thriving in U.S. Department of Agriculture plant hardiness zones 5 through 9. In zones 5 and 6, they can be cut down to the soil and regrow in time to burst into bloom with other roses that require winter protection. They are self-cleaning, so they re-bloom freely without deadheading and summer pruning.
In milder climates, spring pruning keeps Knock Outs from growing beyond their typical 4-foot height and width and becoming leggy. In colder zones, spring pruning trims back winter-killed wood and starts new growth in the right direction.
Knock Outs are resistant to many rose maladies, including black spot, a common fungal disease -- but resistance is not the same as immunity. Like other roses, Knock Outs need at least 6 to 8 hours of sun, good air circulation and an inch of water a week, including rain.
To keep Knock Out shrub roses tidy, you need a sharp pair of hand shears for small branches and loppers for branches 1/2-inch thick and larger. Older gardeners or those with physical limitations can accomplish most cuts with a sharp, long-handled lopper.
Keep tools clean and rust-free for their own good and disinfect cutting surfaces while pruning roses. Dipping cutting surfaces in a full-strength household cleaner or wiping with rubbing alcohol disinfects against viruses.
Long sleeves and rose gloves that cover wrists protect against scrapes from thorns.
The Kindest Cuts
Early spring pruning revitalizes Knock Outs and encourages growth. Cut each branch back as much as two-thirds of its length. In USDA zones 5 and 6, shrubs can be cut back to 6 to 12 inches tall. Make cuts just above growth nodes -- the thickened places where leaves and branches start -- and choose nodes that point outward to keep the interior of the shrub open for light and air circulation. Always cut on an angle away from the growing side of the node so moisture drains off the cut surface and away from growing surfaces.
Plan your pruning for very early spring -- before shrubs begin actively growing. In USDA zone 9 gardens, where pruning is a matter of shaping rather than renovating, prune Knock Outs in December and early January. Plan USDA zone 5 pruning for late winter in early February. In other zones, aim for very early spring when daytime temperatures stay above freezing, but before growth begins.
If you have not cut your Knock Outs back each year, take several of the oldest, woody branches each year to renew the plant on a more gradual basis.
Clean out dead or damaged wood anytime of year.
- Missouri Botanical Garden: Rosa “Redrazz” Knock Out
- Missouri Botanical Garden: Rosa “Radyod” Blushing Knockout
- Washington State University Puyallup Research Center: Sterilized Pruning Tools: Nuisance or Necessity
- North Carolina State University Cooperative Extension Service: Pruning Knockout Roses
- Louisiana State University Agricultural Center: Knock Out Roses Do Require Pruning
- Oklahoma State UniversityExtension Tulsa Master Gardeners: Knockout Roses
- Photo Credit boonsom/iStock/Getty Images
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