Knockout Roses – What You Need To Know About Them

knockout-roses

Knockout Roses seem to have taken the rose growing world by storm as one of the easiest, trouble-free rose plants to grow. Apparently this AARS award winning rose is the most widely sold rose in North America due to its hardiness and versatility.

This rose was hybridised by Willian Radler and introduced to the world in 1999. It’s a floribunda rose that grows to about 4ft tall (1.2m) and as wide, forming a small compact bushy plant.

Flowers are semi-double and loosely formed, cherry-red fading to pink as it ages. Many clusters of flowers are borne on the plant which have very little fragrance. If they’re not regularly dead-headed they will set hips in shades of orange.

Knockout Roses are a very versatile. They can be planted in rows as a border or hedge, where they look terrific en masse. They are also compact enough to be grown in containers on patios and decks where their non-stop blooming can be shown off to advantage. You can also buy them in tree form as a standard rose.

They are supposedly shade tolerant, resistant to black spot, mildew and rust. Though a lot of this depends on them being planted correctly and having their cultural requirements met - there are cases where this rose does get disease problems but it is less prevalent to disease than some of its fussier counterparts.

Knockout Roses are said to be “self-cleaning” meaning they don’t need deadheading, but to promote continuous flowering I would recommend lightly deadheading this rose bush during the growing season, with the emphasis on “lightly” as the flowers bloom on new wood. If you don’t deadhead, the rosehips use up a lot of the rose’s energy (forming new seeds within the hips) instead of the plant’s energy being used to form flowers.

They are supposed to be hardy down to USDA zone 5, however the occassional loss does occurr in this zone over the winter so I’d be inclined to cover them during that season to prevent any losses occurring with your knockout roses.

50 Comments so far

  1. Christine Kirk on May 26th, 2010

    We had professional landscaping done at our home last year. Four knockout roses were planted as part of this landscaping. We have tried repeatedly to contact our landscaper, without any results. The rose leaves are covered with small holes and most of the leaves are dying. These are not aphids, as I know what they look like and we have no evidence on the leaves. The blooms are not affected, but are becoming very sparse. Any suggestion as to what may be causing this and is there any treatment?

  2. admin on May 26th, 2010

    @Christine
    It’s hard to diagnose the problem without a picture of it but it could be some kind of leaf spot fungus that is causing the leaves to get small holes in them so you might want to try using a general fungicide on both the tops and underside of the leaves. Is there any discoloration around the small holes? Anthracnose can cause leaves to get a shot-hole appearance to them but this fungal disease starts with small purple/black circular spots appearing before the centre of the spots dry and fall out, and you haven’t mentioned if the holes have a purple edge to them. The leaves also tend to go yellow so are any of the leaves yellowing? Are the leaves skeletonized (rose chafers or Japanese beetle) or are they definite holes? The leaf cutting beetle chews neat circular pieces from the edges of the leaf but not in the middle. It sounds more like a fungus to me than an insect causing the damage, so I would try spraying with a fungicide. Ask at your local nursery for a reputable one and always follow the safety and usage directions on the pack

  3. Betty Reed on June 22nd, 2010

    When do I prune my KNOCK OUT ROSES?

  4. admin on June 22nd, 2010

    @Betty
    It depends where you live. In Australia – in warm climates like Sydney – prune in mid winter. In the colder climates of Australia, prune after the last frosts.
    In warm US climates like Florida and Arizona prune in late fall or early winter. In moderate US climates early spring is the best time to prune, and in the colder northern climates of the US where roses have to be covered over winter, it’s best to prune them after the hard freezes are over or when the Forsythia starts to bloom.
    The above give a general idea, but to be absolutely sure of the best time to prune in your particular area, I’d visit or phone your local plant nursery and ask the horticulturalist there; that way you’ll know you’re pruning them at the perfect time for your area and can get them off to a good start.

  5. Gail Sklodowska on October 20th, 2010

    Thanks for the helpful website. I purchased 3 Double Knockout Roses (Resa Radtke) for my patio and absolutely loved them. Since these are in containers and I live in Zone 5, I would like to try to overwinter them. The tag notes they are hardy to Zone 4 so I have the choice of planting them in the ground at a friends or placing them in a garage. Could you provide your advice? I have read that I should wait till the plants are dormant. How do I know when that is.

    Thank you,
    Gail

  6. admin on October 20th, 2010

    Hi Gail
    I’m glad you have found the website helpful. Seeing your roses are already in containers I think it would be a lot easier to just leave them in these and put them in the garage or basement when the outside temperature gets into the mid teens in November. Your roses will become dormant around November, so put them indoors then. Then when spring arrives put them back outside again, but wait til the frosts are finished.

  7. Lisa Schilling on April 16th, 2011

    I live in Birminham AL. and the roses i have look similar to these, but are white in color. I have never taken care of roses before and am curious if the are a variation of the knock out roses.

  8. admin on April 17th, 2011

    Hi Lisa
    your white roses, though they may look similar, wouldn’t be knockout roses, as there are no true white ‘knockout’ roses on the market as yet.

  9. Tamara on April 30th, 2011

    Just planted some double knock out roses a couple of days ago. The soil I planted in was kind of clay like so I mixed with miraclegrow potting soil. I watered the roses once the day I planted and two days later which was this morning. This afternoon two of them look like they are dying. wilting branches…a couple of dry flowers and some powdery leaves. Any idea what I’m doing wrong? Did I over water?

  10. admin on May 20th, 2011

    Hi Tamara
    it sounds like your roses have got powdery mildew on them since you mention that they have powdery leaves. Powdery mildew while not fatal to your roses, will attack new and old growth including new developing shoots and buds, leaves and flowers and causes distorted growth that is covered in a white/grey powder-like substance. Spraying with a fungicide should help to control it. Also make sure your roses are planted in an area that gets plenty of sun and has good air circulation (don’t plant too closely to other plants). It doesn’t sound like you overwatered them but to be sure you don’t, always check the soil first by poking a finger down to your knuckle – if the soil is moist then don’t water. This disease is more prevalent at the beginning of Spring when temperatures are starting to warm up. In the heat of summer it never seems to be a problem.

  11. Linda on June 21st, 2011

    I am from WV and my 2nd year knockout roses were beautiful until a few weeks ago. Once bush is completely brown (dead) and the leaves have tiny holes in them. Now some of the leaves are turning yellow and have a few black spots on them. Help! I don’t want to loose them. Thank you

  12. admin on June 23rd, 2011

    Hi LInda
    sorry to hear about your roses. The tiny holes could be caused from anthracnose, a fungal disease where purple or brown fungal spots develop on leaves then dry out creating holes in the leaves; use a fungicide to control this. They could also be caused by japanese beetle – look for any evidence of these and spray plant with a systemic pesticide if evident. The black spots sound like the fungal disease black spot; spray with a fungicide to manage this.
    When you say one of the plants is dead/completely brown; these diseases should not kill a plant outright and it seems unusual that one would die and others arent dead so I’d do a little more investigating. Have a dig around the soil; is it draining OK/getting enough water down to the roots? You haven’t used any herbicide around that plant? anything else different on that plant compared to the others? Good luck.

  13. Kris on July 6th, 2011

    I planted a knockout rose early last fall. It bloomed wonderfully before going dormant in about November. This spring landscapers pruned it and it started to grow lush green leaves and bloomed for one cycle in May. Since that time, it will not bloom again, it is not forming any blooming buds at all. Several of the leaves and branches have turned purple and the buds form only more leaves (purple also). There are still some green leaves. Any idea what is causing this and how I can correct it? Thank you!

  14. admin on July 7th, 2011

    Hi Kris
    The purple leaves could be caused by a couple of different things; sometimes new leaf growth can be a reddy purple color, though the leaves should turn green as they grow larger and mature. If this is not happening, then it could be the fungal disease downy mildew. Downy mildew can cause purple streaking on the stems, and purple angular areas on the leaves and buds. It can be bought on by moist humid weather, coolish nights and warm/hot days. If it is downy mildew, you will need to spray a fungicide to try and control it. Ask at your local garden centre for one they recommend.

  15. Mary on July 28th, 2011

    I’m sorry if I am beating a dead horse, but I have three Knock-out Roses that I bought and set out a few months ago. I have fertilized them with fertilizer specifically for roses and was careful with amounts. They have been watered regularly. Two of them are beautiful, prolific bloomers. The middle one, however, has fewer blooms and its leaves are covered with ragged-edged holes. It looks like something is eating its way all the way around some of the leaves. On others, it eats from the edge toward the center. On still others, the holes may be only in the centers. They are all very ragged, though, wherever they are. I have not found any insects or worms on the plant. Can I treat it or should I dig it up and replace it. Whatever it is, I don’t want it to spread to the other two.

    We did have a long period of drought and now we are having an unusual rainy period with lots of flash flooding. The bed is raised and well drained, but still they have been getting a lot of rain. I live in south Mississippi.

  16. admin on July 29th, 2011

    Hi Mary
    it sounds like you’re doing everything right for your roses however something is definitely eating your rose leaves so you may want to use a systemic pesticide designed specifically for rose pests on the plant before the pest starts on the other roses next to it. It’s no point getting a contact spray seeing you can’t see any evidence of the insect on the leaf and you need to spray the insect itself for contact pesticides to be effective. A systemic pesticide will kill the pest when it chews on the leaves. Ask at your local hardware store or nursery for the best one to use and follow the directions on the pack.

  17. Ginny Lee on August 1st, 2011

    This spring I bought a yellow knockout rose and planted it between two climbing yellow roses. All are fed the Bayer rose food. The knock-out suffers yellow leaves with black spots. Years ago I learned to pick the damaged leaves off so they would not contaminate the soil and the other bushes. The food and tender care is not enough. The climbers continue to do well. What next? Thanks.

  18. admin on August 1st, 2011

    Hi Ginny
    You’re doing the right thing picking off the damaged leaves; also pick up any that fall on the ground. First off, how close have you planted the yellow knockout to the climbing roses? In hot and humid climates roses need good air circlation and should not be planted too close together, so make sure there is plenty of air circulation between your roses. The next line of defense against black spot is to use a fungicide to try and control it. Unfortunateley growing roses in areas of heat and high humidity does make them more prevalent to fungal diseases and the need for fungicides. Use one designed specifically for black spot/rose fungal diseases and follow the recommended dosage rates and spray frequency on the label. Using lucerne as a mulch also helps to stop any black spot spores being splashed onto the lower branches when it rains, and some rose growers swear that there’s something in the lucerne that helps reduce the incidence of black spot on their roses.

  19. Joyce on September 14th, 2011

    Two of my double knock out roses I am told have a fungas. The roses have shriveled up leaves and flowers that seem that have a very curly appearance. Also, the stems have an unusual amount of thorns on them. I was told by a friend that this is a fungas and I should be cautios not to prune the other roses with the same shears as it will spread the fungas. Is there a product I can apply to the affected roses, or do they have to be dug up and replaced?
    Thank you.

  20. admin on October 5th, 2011

    Hi Joyce
    It sounds like your knock out roses have definitely got a problem. Have a good look at the problem ones to see if you can see any sign of a pest that is causing the problems; if there is no evidence of a pest then it’s probably a fungal disease. Before digging up the roses, try spraying them with a fungicide that is made for roses and follow the directions on the label re dosage rates and frequency of spraying. If after a few weeks the roses don’t respond favorably, then you may have to dig them out. Your friend is right re not using the same pruners on the other roses, as disease can be spread to your other roses. I always wipe the blades of my pruners with a cloth dipped in methylated spirits before pruning or deadheading the next rose so any pathogens that may be on one plant aren’t transferred over to the next.

  21. Paula on October 15th, 2011

    Hi, I recently purchased and planted two Blushing Knock Out roses. I live in SE Michigan and the nursery told me to plant them right away, which I did this week. So far, they look great. Here’s my question: I ordered one more which is not scheduled to ship until Nov. 9 and am wondering if I should also plant that one or keep it inside until spring? Also, should I cover the other 2 for the winter (I put a lot of mulch at the bases)? Thanks in advance!

  22. admin on October 16th, 2011

    Hi Paula
    I’ve given a more in depth answer to your questions here winterizing knock out roses, but in short I wouldn’t plant the one you just ordered; just keep it in the garage until spring, and yes, I would cover the ones in the ground for the winter.

  23. Joanna on March 6th, 2012

    My knockout rose has been damaged by my neighbor’s tree removal service. Basically a couple branches have broken, one near the base, and it has come up slightly from the ground. I pushed it back in. It is brand new and only been in the ground a few weeks. Should I just trim the branches and hope for the best?

  24. admin on March 6th, 2012

    Hi Joanna
    Your knock out rose should be fine. Cut below the damaged stems (to the next bud or leaf junction) with a pair of sharp pruners, leaving a nice clean cut. It wouldn’t hurt to give it a drink of liquid seaweed (just mix some up in a watering can at half the recommended strength) to give it a boost and help get it over any shock.

  25. Kelly on April 4th, 2012

    I just purchased three knockout roses. I have a very large pot that I would love to be filled with these roses. All three plants fit in this pot with several inches around each plant. I am anxious to have the pot filled with roses even though it is recommended to plant the roses a few feet apart. Would it be okay to plant all three in this pot? Or do they grow and expand quickly if I just planted one? I live in central Texas. Thanks!

  26. admin on April 4th, 2012

    Hi Kelly
    Knockout roses can spread 3 foot in diameter so you can’t put them all in the same pot; just one would go in the pot. You’ll have to exercise some patience and wait for it to bush out, which could take a few months, but it will be worth the wait.

  27. DANNY PENNELL on April 5th, 2012

    Your info. is very helpful. I live near Richmond,VA and this year we are having an infestation of “inch worms”. They are eating my knockout roses.The leaves and the stems. What can I put on and around the plants to get rid of them and to keep more inch worms from getting on them?

    Thanks.

  28. admin on April 5th, 2012

    Hi Danny
    You can either pick them off daily and squish them or put them in a bucket of soapy water if you want to go with an organic solution or you can go to your local garden centre and buy a systemic pesticide to spray on them; systemics are absorbed into the plant itself so that when the inch worm chews the leaves they die. Follow the spraying schedule recommended on the label of the product.

  29. nancy huyser on April 19th, 2012

    I purchased 3 knockout roses last year. We had an exceptionally warm March. I pruned them back and they looked great. April we had 3 nights of below 32 temperatures. They looked wilted. I trimmed the wilted leaves and small stems. Now they look wilted again. Did I kill them or will they come back. Thanks

  30. admin on April 19th, 2012

    Hi Nancy
    The only way you’ll find that out is if they don’t put on new growth in the coming weeks; then you can assume they are dead. Don’t do any more pruning of the stems for the time being; just pick off any wilted leaves, water them regularly (but take care not to over-water them).

    Definitely don’t fertilize them but do give them a weekly dose of liquid seaweed made up at half strength after one of their regular waterings. Liquid seaweed is a great tonic for plants under stress so use that and monitor them over the coming weeks. Hopefully they will respond with new bud and shoot initiation. Once they seem to get going again, cut off any dead looking growth from the top of the stems down to just above any new buds or shoots. Good luck with them and let me know how you go.

  31. S Mathieson on April 20th, 2012

    These roses are beautiful to look at but no one has commented on whether they have a fragrance.

  32. admin on April 20th, 2012

    Hi S
    In the article above, third paragraph down, fragrance is touched on: “Many clusters of flowers are borne on the plant which have very little fragrance.”

  33. Ashley on April 21st, 2012

    I planted my double knockout rose bush 2 days ago and the leaves are drooping and so are the rose buds. I have clay soil so I dug the hole and planted my rose bush and filled the hole back up with garden soil and “black cow” (brand name) manure. Did I do something wrong. I have watered everyday also

  34. admin on April 21st, 2012

    Hi Ashley
    I’ve answered your question in more detail here.

  35. Thomas on May 4th, 2012

    Hi,

    I purchased knockout roses about two weeks ago. I haven’t planted them yet, they are sitting on my patio (1st week shade/ 2nd week full sun). I’m not sure what happened but they looked very healthy when I purchased them. They were starting to bud during first week but over the weekend I noticed that the buds are dying and the leaves are also withered and dying. I was watering them once a week and it also rained a few days last week. I have since removed the dead leaves, etc. I also checked the soil and I noticed that is was semi-dry. Since I noticed the withering/dead leaves, for the past two days I’ve been watering them every other day but I’m afraid of overwatering. After watering, I check the soil and its semi-moist but the next day it feels somewhat dry again. Maybe I’m watering too little? Is there anything I can do to help them recover? Thanks!

  36. admin on May 4th, 2012

    Hi Thomas, the reply I gave was a bit too lengthy to put here in the comments section, so you’ll find it here.

  37. Kevin Harrold on May 11th, 2012

    I have 7 double knockout roses that are 3 years old (red) that are appearing to revert to a “wild rose” with single 1 1/2 in. size blooms. Some/many of the blooms have white streaks (almost verigated) on them. The leaves even don’t appear “normal” they appear smaller (like a wild rose). This seems to be the case with 2 to three of the seven. Could the low temputures we saw this spring have caused this (Muncie area, Indiana)? Any ideas? We have always loved these roses and hate to see them go! I can send pictures if needed. Someone help…my roses are mutating!

  38. admin on May 12th, 2012

    Hi Kevin
    The knockout roses you planted must have been grafted for them to have reverted back to the rootstock. What can happen in cold climates is that a freeze can kill the canes that have grown from the bud union (the knobbly bit towards the base of the main stem that your knock out rose stems grow from).

    When this happens the rootstock takes over and come spring the new growth comes from the rootstock (usually rosa multiflora – that has been used as the base on which the buds of a knock out rose have been grafted). That is what you are seeing now.

    A way to prevent this from happening in the future is to winterize your knockout roses which I have written about here so that a freeze doesn’t kill off any of the stems that have grown from the bud union.

  39. Patty Foggin on May 19th, 2012

    I have beautiful Knockout Roses. They are two years old. They are planted twenty feet apart. I lost one last year and in the same spot this year I lost the second. Now this summer the other group is showing the same signs. Dense formation of prickles on the canes and stems. Canes and leaves are deep red and purple in color. Is there any way to save the rest? The tea roses in the same bed are not affected. Thanks so much!

  40. admin on May 19th, 2012

    Hi Patty I’ve answered your question here and also added a photo to explain what causes this phenomena

  41. Nancy on June 11th, 2012

    Hi,My knock out roses have holes in the leaves and small rust spots. I took to the garden center and they gave me a spray to kill the insect that was doing the damage. Should I pick off the damage leaves? Will they grow back? Thanks

  42. admin on June 12th, 2012

    Hi Nancy
    It’s up to you. You can pull the most damaged looking ones off if you like, but don’t pull them all off as the rose plant needs leaves on it for photosynthesis to occur; esp at this time of year in the northern hemisphere when the plant is growing.

  43. BERNIE ECKBERG on June 25th, 2012

    I have noticed that one of my knockout rose bush continues to send up huge shoots with no roses on it. I clip it off a few weeks ago, and noticed that there were several more shoots with no roses forming. What gives?

  44. admin on June 26th, 2012

    Hi Bernie
    It sounds like your knockout rose is sending out “suckers” from the root stock. The way you can tell for sure is to check the point from which the sucker is growing. If it is from below the bud union (the knobbly bit where the canes originate from) then it is coming from the rootstock of the plant and is definitely a sucker and needs to be removed from the point at which it’s growing. To make sure it doesn’t grow back you need to grab the sucker at the base and pull it away from where it’s joined to the plant. You don’t want to cut if off as that will just encourage the shoot to keep growing.

    Just be sure it’s not a basal shoot. You can tell a basal shoot by looking to see where it is growing from. If it’s is growing from the bud union itself where the rest of the canes are growing from, then it is a basal shoot and part of the grafted knockout rose. You want those to remain on the bush to form part of the framework of the bush which will produce future knockout rose blooms.

  45. JENNY on July 9th, 2012

    i’ve had double knockout rosesin my flower bed for 3 years now. i have one issue- the stems are growing way too thick and the leaves are a burgundy color also the blooms are very compact. i have pruned them after every growing season , i think i cut them back too far. can i fix this issue

  46. admin on July 10th, 2012

    Hi Jenny
    According to the developers of the knock out rose series it is safe to prune them down to about 12 – 18 inches. That shouldn’t make the canes grow too thick but you could try experimenting and not pruning them down as low to see if it makes a difference to the thickness of the stems. Please let me know if it does make a difference. The new growth on knock out roses always seems to be burgundy before the leaf matures a bit more and greens up. You can see a pic of burgundy colored new leaf growth here.

    I’m not sure what could be causing the compact blooms; are you regularly fertilizing them with a good quality fertilier every 6 weeks during the growing season as well as watering regularly during the hot summer months? Giving the knock out rose enough water and fertilizer should result in abundant flowers with normal blooms.

  47. Lori on August 23rd, 2012

    HELP! Live in Mississippi on the Gulf Coast and planted lots of knock out roses in the front of the house in the spring, 3 of them hasve lost all their leaves and have no flowers. Any suggestions?!

    Lori

  48. admin on August 25th, 2012

    Hi Lori
    Have you been giving them enough water through the hot summer? Depending on the soil type your roses are planted in, they may need watering on a daily basis in extremely hot weather. Does the water drain effectively? Have a thorough look over the plants for any sign of pest or disease to see if that could be causing the leaves to fall off the knock out roses. Diseases like black spot (whcih can cause leaf yellowing and leaf fall) are prevalent in hot humid climates and even though knockouts are marketed as disease resistent, they can still succumb to this disease when the conditions (like heat &humidity) are present.

  49. virginia on September 13th, 2012

    i have not read any comments on watering. ilive in ga. knockout roses wereplanted facing the west.wsome of the leaves are turning yellow and some have black spots.please respond to watering and the problem re:possible fungus,

  50. admin on September 14th, 2012

    Hi Virginia
    Watering is dependant on the climate of your area and the season. It’s hard to give a blanket reply to watering as different gardens have different microclimates within a garden itself, so the best way to tell when your knock out roses need watering is to stick your finger in the soil they’re growing in and if it’s on the dry side, water them. In summer you should do this every couple of days, until you get to the point of knowing how often to water them. The same goes for the cooler seasons; check the soil every few days until you get a knowledge of your gardens particular watering requirements. A good deep soak is preferable to a quick watering.

    If your roses have black spots on them, it’s probably the fungus called blackspot. You can read more about it here.

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