UACES Facebook Knockout Roses

Knockout Roses


July / Aug 2016


Many of my roses from Knock-outs to hybrid teas have been diagnosed with rose rosette disease.  I first noticed that some of my roses in the front yard looked kind of odd--there were strange branches shooting out which had a very pink stem with a lot of thorns.  The cluster of roses formed in a tight ball at the top. I thought that the Knock-outs were resistant to all diseases.  What should I do now, remove all my roses?


To my knowledge, no roses are totally resistant to rose rosette.  Some are more susceptible than others, but they can all get it.  The disease is a virus, and there are no sprays or cures for viruses.  It is usually spread from insect feeding, particularly a mite. We have been seeing more cases of rose rosette in recent years, but that could be attributed to the fact that because of the carefree roses like Knockouts and Drift roses, more roses are planted in our landscapes.  It could be a combination of things.   Drier years tend to give us a larger mite population and we had an extremely mild winter. Secondly, there are a lot of roses in our landscapes.  The success of the Knock-outs as long season, almost bullet-proof plants, has led to a lot of these planted in our landscapes.  As with any disease, you have to have a susceptible host, the right environment and the introduction of a pathogen.  If you have a lot of host plants, when a disease hits, it can multiply.  You are correct in that there is no cure.  I am not sure you need to remove all roses from your landscape, just those affected.  Proper pruning of roses in late February and spraying to control mites can also help. 

June 11, 2016

QuestionMy aunts knockout roses have diseased looking leaves, can't find specific online match. Can I send you photos for a diagnosis?



If you have plants which seem to be diseased, take a sample in to your local county extension office.  The best days of the week to take in samples are Monday and Tuesday so that the samples can get to the lab quickly without lingering in the mail over a hot weekend.  If the local agent can’t identify the problem, they will send it to our disease diagnostic lab in Fayetteville.  Once the plant pathologist has determined the problem, you will get an email with a diagnosis and control method.  This is currently a free service. 

(November 2012)

QuestionI rooted a cutting from a knockout rose this year and planted it in a pot on my patio. It has bloomed all summer, can I safely move it now to a flower bed on the west side of my house, and expect it to live through the winter. I live in Little Rock.

AnswerYes, plant it in the ground, mulch it and water if dry and it should do well. Wait to prune it back in late February. Even though we don’t prune Knock out roses as severely as hybrid tea roses, they do need to be pruned by at least 1/3 – ½ every year before growth kicks back in.

(September 2012)

QuestionMy Knock out rose bushes have only bloomed once so far this season. Can you please advise me what the problem is?

AnswerThe intense summer we had has impacted many flowering plants. Whether it is roses, crape myrtles and even some annuals, they slowed down or stopped blooming just to stay alive. Now that we have gotten some rain, the temperatures are cooling off, hopefully they will rebound and bloom through fall.

(August 2012)

QuestionOur knock-out roses have had the wind knocked out of their beauty by this year's drought. We have a dozen plants along the fence line that receive full sun from 8am to 6:00pm! They were planted May, 2011 and we babied them through the hot summer last year and won that war. We use a soaker hose rather than above ground watering. Where do I go from here to try and save them from further drought damage? You can see the yellowed/scorched leaves, the bare canes!! Can they be pruned now? Can they be revived at all?

AnswerThis question and answer are similar to the butterfly question above. Knock out roses should be pruned by at least 1/3 every year in late February. Right now, a light corrective pruning can give them the chance to produce foliage instead of flowers and get a bit more attractive. Once the cooler weather kicks in with some rain, they should begin to bloom again. For now it is a temporary fix, but by next Feb, you can do more severe pruning. Fertilize them lightly now as well and they should begin to bounce back. All the watering we have done this season has also leached out the nutrition of our soil and roses can take one last application of fertilizer now.

(Aug. 2012)

QuestionMy knockout roses are staying alive, with a little watering, despite the punishing summer. They would probably look better if I deadheaded them aggressively, as well as maybe blooming more later. Or should I leave them in place to produce hips for wild animal/bird food. Should I deadhead my other roses, the climbers and the shrubs and teas? I usually leave them pretty much alone, but they are pretty neglected concerning feeding and pruning.

AnswerMany rosarians do a little corrective pruning, both deadheading and thinning a bit of the rose plants in the heat of summer. This lets the plant conserve some of its resources, gives it a fuller foliaged plant and allows for better blooming when the temperature eventually breaks in the fall. Keep in mind that when a plant is blooming, its main resources go to the flowers. Some of our roses can get a little leggy by late summer, and could use a little more fullness of foliage. Don’t get carried away and do extensive pruning, but a little corrective pruning may be just what the doctor ordered. Continue to water and if it isn’t too awfully hot, give them a light dose of fertilizer as well. Knockout roses usually don’t form rose hips, since they are “self-cleaning” which means they don’t set seeds, but try to continually bloom. The only roses I would not prune are the climbers, especially those that only bloom in the spring, as you could interfere with flower set.

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