Double knockout roses are a hybrid shrub rose that grows 3 feet tall and equally as wide. It produces double pink blossoms starting in July and has recurrent blooms until frosted in October. It likes moist, well-drained soil and is an extremely hardy rose bush. It was bred to be disease-resistant and tolerant of light shade. It does require four hours of sunlight a day to thrive. It does not require heavy duty maintenance. Double knockout roses are self-cleaning and do not need to be deadheaded to continue blooming throughout the growing season.
Water the soil directly with a soaker or drip hose. This keeps the foliage and blossoms dry which prevents disease. Double knockout roses do best with uniform soil moisture. It takes about 1 inch of water each week to grow a healthy rose bush. During hot temperatures, the rose bush will need to be watered more frequently than during cooler weather.
Spread 2 to 3 inches of mulch around the base of the rose bush. Use long-lasting mulch like wood chips, straw or dry grass clippings. Decorative mulch like shredded hardwood bark or cocoa bean hulls can be used as well. This helps to retain soil moisture, keeps soil temperatures constant and reduces weed growth.
Feed your double knockout rose bushes with a general-purpose fertilizer like 10-10-10 or 12-12-12 when the leaves begin to show in the spring. Spread 1/2 to 1 cup of fertilizer around each bush. Start at 6 inches from the crown of the bush and go out to 18 inches. Work the fertilizer into the top inch of the soil and water thoroughly. Feed your roses again in mid-June and then in mid-July.
Encourage your double knockout rose bush to go into a dormant state in the fall. Stop deadheading and cutting flowers after October 1. Allow your rose bush to form hips. Once the ground freezes, remove foliage and other debris from around the plant. Mound 12 to 24 inches of straw over the rose bush.
Remove the winter mulch from around the rose bush in the spring after the danger of winter freezing has passed. Prune a third of the oldest canes to the soil line every three years. This keeps the rose bush open and encourages new cane production.