Knockout Roses – What You Need To Know About Them
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.
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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?
@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
When do I prune my KNOCK OUT ROSES?
@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.
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
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.
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.
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.
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?
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.
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
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.
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!
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.
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.
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.
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.
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.
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.
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.
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!
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.