Knock Out rose bushes, hybrid shrub roses first bred by William Radler in 2000 and sold by the Conard-Pyle Co., have become one of the best-selling roses of all time. They require minimal care, tolerate drought and heat, and resist pests and diseases. In 2000 and 2007, the Knock Out rose won the All-American Rose Selection Award. These roses produce a multitude of cream, pink or red blossoms nearly year round in warm climates. Hardy in zones 5 through 9 in the United States, Knock Out rose bushes thrive with little maintenance once established.
Plant Knock Out rose bushes during mid-spring in a location that receives at least six to eight hours of sunlight each day and consists of well-drained, moist, fertile soil for maximum growth. Space Knock Out rose bushes 3 to 5 feet apart to accommodate their full spread.
Spread a 3-inch layer of organic mulch such as shredded cedar over the ground surrounding the plant in late spring to help stunt weeds and retain moisture through the hot summer months. Begin the mulch about 3 inches from the plant's base to minimize disease vulnerability.
Water Knock Out rose bushes once every seven days during the first season of growth to help them become established. Decrease the watering frequency thereafter to once every two weeks. Increase watering again to once per week when temperatures rise above 90 degrees F, as the plants require more water during extreme heat.
Feed the shrubs once per year during spring, just after new growth begins, using a balanced 10-10-10 NPK fertilizer to provide proper nutrition for root and flower development. Apply at the rate described by the manufacturer for the best results. Knock Out roses are not heavy feeders, but blooming increases with annual fertilizing.
Prune the rose bushes once every three years during early spring, immediately after the threat of winter weather has passed. Use hedge clippers to remove all damaged, dead or diseased limbs and cut back any excessively long or untidy growth. Conrad-Pyle recommends cutting them back yearly to about 18 inches for maximum performance.