Roses are prized for their season-long color, especially with the advent of easy-care varieties such as Knockout, which provide flowers from May through November. Every year the Johnson County Extension office receives a number of questions about fall care.
The most common is about pruning. Fall pruning is not recommended. Roses are best pruned in late winter or early spring, just before new growth appears. Fall pruning can increase the risk of winter injury, because the cut stem does not have time to properly seal.
Knockout roses, however, can grow bigger than expected. It is not uncommon to find them 5 feet high and wide. People often plant them along a walk or driveway and then the bush grows too large, reaching out and grabbing passersby or scratching vehicles.
If canes pose a hazard, cut them back to 18 to 24 inches to eliminate the problem. Then make your final cut next year, removing the winter dieback and shaping the bush.
Winter mulching of roses was recommended for a number of years, but modern easy-care roses seldom need additional winter protection. Older rose varieties, many of which were grafted hybrid teas, require the winter covering to protect the union between the rootstock and named variety. If the grafted variety dies over the winter, then the plant will be lost.
A winter mulch layer should consist of a 6 to 8 inch mound of soil over the center of the plant. This layer of garden soil protects the tender graft from the fluctuating temperatures and extreme winter cold.
Modern easy-care roses are grown on their own roots, so if the plant does died down to the ground, the plant should send up new shoots from the base. As a result, mulching for the winter is no longer needed, though it won’t harm the plant.
Easy-care roses such as the common variety Knockout should be thought of as a shrub. Shrubs are not pruned in the fall and rarely need mulch. Shrubs need adequate soil moisture for winter survival. These plants are very adaptable in our climate.
Enjoy the last of the season’s flowers and let nature take its course. But be ready to prune come spring for another season of color.
Dennis Patton is a horticulture agent with the Kansas State University Research and Extension. To get your gardening questions answered on The Star’s KC Gardens blog by university extension experts, go to KCGardens.KansasCity.com.