A knockout rose grows to about 4 feet high, and it blooms for most of the spring and summer months. Knockouts grow fast and are tolerant of most types of soil. The natural shape of a knockout rose is circular, but they tolerate pruning well, allowing you to achieve a fuller shape while increasing their vitality.
Knockout Rose Soil
Before pruning a plant, make sure it is planted in fertile soil. The soil quality affects how quickly the plant can put on new growth after trimming, or whether the plant can survive the grooming at all. For best results, treat your rose every 2 to 4 months with cotton seed meal, an organic fertilizer that contains most of the nutrients required for plants.
Prune for Health
Ideal plant health requires pruning to remove dead and damaged leaves and limbs. When dead or damaged leaves and limbs are left on the plant, they continue to draw nutrients away from the plant, and serve as a beacon to insects and plant disease. When pruning, use the 1/3 rule, which says you can cut back up to one third of the total growth on the plant without causing it serious damage. This is especially true with knockouts, which are already resistant to shock.
TIP: Our expert gardening advisor Susan Patterson recommends, "Clean pruning tools with hydrogen peroxide before using."
Prune for Shape
Because of the natural shape of a knockout rose, pruning for shape is a fairly simple job. Just follow the curve of the bush, trimming errant branches. You can remove buds that are past their bloom, but it is not necessary with this plant as the old blooms will fall off on their own.
TIP: Susan suggests, "To prevent borer damage you can seal the cuts made during pruning with some white glue."
How to Prune
When pruning for shape or health, cut branches at a 45-degree angle. Cut to remove straggly or damaged leaves and stems. When cutting back healthy limbs or branches, save the pieces you remove, they can be rooted in potting soil, and produce new roses. Always make your cuts above the leaf branches, to reduce the risk of plant disease and infection. If there are broken branches, trim them behind the break, at the nearest leaf or branch branch.
TIP: Susan adds, "Always use sharp pruners for any rose trimming."
When to Prune
In warm regions, pruning for health and shape is best done before new growth begins in the spring. Light pruning is ok any time during the growing season. For those in the subtropical zones of USDA zones 9 through 11, roses may be pruned at any time.
Care and Feeding
Knockout roses are not demanding. As long as the soil contains sufficient nutrients and is soft enough for the roots to grow, these bushes tend to do very well. Fertilize the soil with compost, and make sure that your plants are getting at least 8 hours of sunlight per day. Fertilize about a week before spring pruning, to make sure that the plants have the available resources to handle the shock of the trim.
photo (c) Eagerwatchdog, 2010 davesgarden.com/members/eagerwatchdog