If you live in a growing zone where the ground freezes, you'll need to cover your Knock Out roses (Rosa 'Radrazz') with protective materials to get them ready for winter. Knock Out roses, including other varieties such as Double Knock Out (Rosa hybrida 'Radtko'), are hardy in United States Department of Agriculture plant hardiness zones 5 to 9. In those warmer zones where the ground doesn't freeze, you might find that the bushes are some of the most carefree plants you have because they won't require deadheading or much special winter care.
Water in Late Fall
The time to start thinking about the winterizing process is long before winter actually arrives. As the temperatures start to drop in the autumn, but before the first hard freeze -- which will be at different times, depending on your growing zone -- give your roses a good, deep watering. Knock Out roses need about 1 inch per week on a regular basis. Moist soil will help protect the plant's roots from damage. Also stop feeding the plants additional nitrogen as the days get cooler.
Tie Canes Together
Knock Out roses can grow as high as 5 to 8 feet tall, possibly putting them in danger of breakage from the weight of winter snow -- but since they're an "own root" species that grow from their own roots, they're vigorous plants that will survive the onslaught. Fall pruning is not recommended, suggests University of Illinois Extension Master Gardener Judy Penticoff on the Rockford Register Star website.
For bush or shrub-type roses -- including Knock Outs -- the Ohio State University Extension recommends loosely tying the canes together near their tops with string, taking care not to bend the canes.
Add Protective Layers
If you live in USDA zone 5 or lower, take additional steps to protect your Knock Out roses. As a general rule, roses need additional protection from the winter cold when the temperatures drop to 20 degrees Fahrenheit for a few days on end, suggests Colorado State University Extension. After tying the canes together, place 8 to 10 inches of garden soil around the bottom of the shrub, or use other types of mulch. Leaves, shredded newspaper, pine needles or other organic matter are all suitable choices. To further protect your roses, cover the entire shrub with burlap material, or purchase winterizing cylinders from a garden supply store. Pile mulch around the shrub, cover with the cone, and then place a heavy rock or brick on top to keep the cylinder from blowing away in the winter winds.
Care for Knock Outs in Warmer Climates
Knock Out roses were designed to be winter-hardy and low-maintenance, so in warm growing zones without a hard frost and plant dieback, you may be tempted to simply leave them to do their thing. But low-maintenance doesn't mean no-maintenance, reminds University of Florida master gardener Paula Wetherby of the Florida Times-Union. In warm climates, you still need to plant your Knock Out roses in an area that gets good soil drainage and air flow and at least four to six hours of sunlight. Wherever you live, your "winterizing" tasks will also include pruning your Knock Out roses in late winter, before new growth appears. Using pruning tools that you've wiped down with a solution of 1 part bleach to 2 parts water, cut the shrub back to half its height and width, making cuts at a 45-degree angle just above a bud nodule.