Benefits & Disadvantages of Knockout Roses

Characteristics

• "Knock Out" roses are both cold tolerant and heat tolerant, thriving in U.S. Department of Agriculture plant hardiness zones 5 though 9. They bloom almost continuously, with a fresh flush of flowers every six weeks, from late spring until the first hard frost. In some climates, they are in bloom for nine months out of the year. The bushes are compact, growing 4 feet tall and wide.

Culture

• Plant "Knock Out" roses where they will receive full or part sun. Unlike most roses, they do well in part-sun locations and will bloom in as little as three hours of direct sunlight per day. They prefer rich, well-drained, slightly acidic soil with plenty of compost mixed in. Water weekly, in the morning, soaking the root ball. Avoid overhead watering, which promotes fungal diseases. Mulch in spring with rich compost to help keep moisture levels even in summer. After each bloom cycle, feed with a fertilizer labeled for roses. Formulas vary, but, in general, rose fertilizers provide a larger amount of nitrogen and phosphorus than potassium. The Portland (Oregon) Rose Society, which makes its own custom blend, offers a 15-10-10 formulation. The society recommends applying it in early spring at a rate of 1/2-cup per established plant, spread out in a 10- to 14-inch area, and repeated at six to eight week intervals. In cold-winter areas, mulch in late fall to protect the crowns. Prune all the canes to 18 inches tall in late winter.

Disease Resistance

• Roses are susceptible to a wide range of plant diseases. "Knock Out," however, is resistant to the common rose diseases of rust, powdery mildew and black spot. Often, it does not need the regular, preventive sprays of fungicide that are necessary for most roses. Good cultural practices, such as providing plenty of air circulation around the plant and feeding, watering and mulching help prevent disease, too. At the first sign of trouble, remove and discard any affected leaves or stems and clean up any fallen plant parts.

Flower Color and Form

• There are seven varieties of "Knock Out" roses. All have single blooms except “Double Knock Out” and “Pink Double Knock Out.” The flowers are all shades of pink or pinkish red, except for “Sunny Knock Out,” which is pale yellow. The flowers of "Knock Out "roses are about 3 inches in diameter, and they are followed in late summer by red-orange hips. They bloom in clusters all over the plant.

Other Features

• The flowers of "Knock Out" roses are mildly fragrant and the foliage has burgundy tones. In fall, the foliage color deepens to red-purple. "Knock Out" is a self-cleaning rose, which means the gardener doesn’t need to deadhead the flowers; they drop by themselves.

Disadvantages

• If you want a traditional tea rose with large, sculpted flowers and deep fragrance, "Knock Out" will disappoint you. "Knock Out" is a landscape rose bush with simple flowers and a light fragrance. It is not a good choice for cutting. Its colors are limited to pink, pinkish red and yellow, so it doesn’t offer the wide range or colors available in other types of roses.