Pruning your Knock Out roses

Story and Photos by Bob Westerfield

If you have had any interest in flowering ornamental plants over the last decade, you are surely familiar with Knock Out roses. They came onto the scene in a big way, promising to be prolific bloomers, virtually disease free, and above all, low maintenance. For the most part, they have delivered. Anyone who has ever grown an original hybrid tea rose knows what a burden they can be to keep alive and healthy. Knock Out roses are light years ahead of the hybrid teas in terms of withstanding the pressures of disease and insects. The newest arrival on the scene is the Double Knock Out rose. Its double bloom more closely mimics the flower of a hybrid tea rose and they are touted as being even more maintenance-free and durable. Even though they are “low maintenance,” Knock Out and Double Knock Out roses benefit from a good pruning once in a while.

This picture shows how to go inside the plant and thin out some of the excessive branches.

Whether you have a Knock Out or Double Knock Out, the pruning method is virtually the same. The good news is that I have seen both these plants butchered by poor pruning techniques and they have come right out of it. Try doing that to a hybrid tea rose and it is liable to become extinct very quickly. 

The first statement I would like to make is that I have grown Knock Out roses for many years and on occasion have left them unpruned for the entire year – they still bloomed and performed flawlessly. The downside of not pruning is that both Knock Out and Double Knock Out roses are aggressive growers and will push out new growth perhaps beyond expectations. Many folks plant these roses too close together or next to a walkway only to find that they can reach a mature size of 4-6 feet in height and spread. This can certainly happen if left unchecked and unpruned. Pruning not only keeps these plants inbounds, it also provides a health benefit to the plant.

Damaged or older stems should always be pruned back to just above a fresh bud.

The ideal time to prune Knock Out and Double Knock Out roses is in the early spring, just prior to new growth. The good news is that if you miss this window of opportunity, these roses are very forgiving, even when pruned basically any time of the year. 

This hardy ornamental branches rapidly, so the first order of business is to don on some leather gloves and go inside the plant to remove some of the adventitious roots. I highly recommend using a quality pair of bypass pruners that are sharpened to a razor’s edge. Avoid using the anvil-type pruners that crush the stems rather than making a clean cut. A good pair of clippers will run you $40-60, but will last a lifetime if properly cared for.

Diseased or damaged leaves or limbs can be pruned out any time of the year.

After removing several interior branches and branches that cross over each other, consider cutting the main trunks back by at least one-third. The time of the year will dictate how aggressively you should prune your roses. If you catch the roses in early spring, prior to the flush, you can literally prune them back like hybrid tea roses if you prefer. This is one way to get an overgrown bush back down to size. 

Be sure to make angled cuts just above a bud. This results in the fastest recovery and creates a surge of regrowth in the spring. Any time you make a pruning cut, be sure to do it just above a bud or branch to prevent leaving a dead stump on the plant. It is also important to select a bud to steer the direction of the plant’s growth. If you select a bud on the outside of the plant and cut just above it, most of the regrowth will shoot to the outside. Conversely, if you select an inside bud and cut above it, the growth will direct toward the center of the plant.

Deadheading may result in larger blooms, but is not really necessary with Knock Out roses. They will bloom regardless.

This is also a good time to eliminate any weak or older canes, allowing a few new ones to take charge. As the season progresses, you can still prune your roses by removing some of the interior branching we mentioned earlier. Any cuts you make after the spring flush will eliminate some blooms, but there will still be flowering during the season. Roses bloom on new wood so they will recover from the pruning and continue to provide a show. 

Whether or not you deadhead your roses as they are blooming has always been a topic of debate. If they were hybrid tea roses, I would definitely suggest you remove the spent blooms as soon as possible. Because of the prolific blooming ability of these Knock Out and Double Knock Out roses, I simply do not have the time to keep up with the deadheading. These plants knock off old buds and continue to bloom throughout the growing season whether you deadhead them or not. Would your blooms be larger if you deadheaded them? Possibly, but you better be prepared to be out there on a daily basis – these things bloom like there’s no tomorrow. 

While Knock Out and Double Knock Out roses are very low maintenance and relatively trouble-free, they are still roses and can have issues. In general terms, be sure to plant them in an area that receives full sunlight and in well-drained soil. These roses enjoy a little fertilizer as they began to flush in the spring and then a few more split applications during the growing season. Like all roses, they prefer a slightly acidic soil. Soil testing can help you determine the exact nutritional needs of your plant.

Shown here is a recently pruned Knock Out rose that has flourished into a more manageable size. Knock Outs can be pruned aggressively like hybrid tea roses, or lightly like floribundas.

While disease and insect resistant, they are not 100 percent immune. Keep an eye on your plants for bugs such as aphids and spider mites. Disease problems can include black spot and certain viruses. Good care and prevention are the best methods for controlling these. 

While Knock Out and Double Knock Out roses are not exactly problem-free silk flowers, they are pretty darn close. In a world that loves roses, they are one of the greatest “inventions” since the automobile. With a little care and proper pruning, you can keep these beautiful plants blooming in your landscape.

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