Pruning ‘Knock Out’ Rose — When, Why, and How

March 26, 2015 | By | Comments (40)
'Knock Out' rose

‘Pink Knock Out’ rose. Photo: Steve Bender

Faithful reader Mandi Villa writes, “I love my ‘Knock Out’ rose, but it’s getting too big. Can I prune it without killing it?”

Yes, Mandi, you can. In fact, you can do almost anything to a ‘Knock Out’ rose without killing it short of rocketing it into the sun. But if you want it to follow the pruning with scores of blooms on a tidy plant, you must follow Grumpy’s rules on when, why, and how to do it.

When To Prune
‘Knock Out’ (red, pink, double, etc.) blooms on new growth. This means that you can prune it almost anytime you want without ruining the season’s bloom. If you prune now, you’ll remove some flower buds and delay flowering, but you’ll get lots of blooms in a couple of weeks. During the growing season, ‘Knock Out’ typically explodes in bloom for a few weeks, goes into a resting phase, and then explodes in bloom again. A resting phase is a good time to prune. About the only time not to prune is late summer and early fall, as this might encourage late growth that wouldn’t harden off in time for winter. In the North, winter is not a good time to prune, but winter is just fine in the South.

Why To Prune
Although ‘Knock Out’ is marketed as a compact shrub, over time it gets pretty big. A neighbor of mine has a ‘Knock Out’ hedge that’s six feet tall. So periodic pruning is necessary to keep it manageable. ‘Knock Out’ also tends to produce a lot of fruit, called “rose hips,” that inhibit future flowering. Trimming these off brings it back into bloom.

How To Prune
First, put on some heavy leather gloves. Grumpy only knows of one thing possessing more vicious weapons than the thorns of ‘Knock Out’ rose.



And that would be Wolverine.

Now that you have gloves on, let’s proceed. Use a good pair of hand pruners to shorten small branches a half-inch thick or less and loppers for thicker ones. Cut back to a leaf or an outward-facing bud. Remove dead, crowded, or crossing branches to open up the plant’s center. Cut back aggressively if you want, but not down to the graft union. That’s the knob at the base where the roots and stems meet.

What’s In A Name?
A while back, Grumpy received a nasty letter from lawyers representing the outfit-that-shall-remain-nameless that patented this plant. This notice informed me that I had willfully misspelled the name ‘Knockout’ instead of the correct way, ‘Knock Out,’ and demanded immediate remediation. You can see why spelling it the former way could cause an asteroid to slightly alter its orbit, smack into the Earth, and extinguish all life.

Here’s the ironic part. The official registered name for this cultivar of rose isn’t ‘Knock Out.’ That’s the marketing name. The cultivar’s true name is ‘Radrazz.’ Therefore, I suggest all of you ask only for ‘Radrazz’ rose when you visit your garden center.

Wouldn’t that be fun? I imagine the exchange would go something like this.

You: “Do you have any ‘Radrazz’ roses?”

Salesperson: “What?”

You: “‘Radrazz’ roses. They bloom all summer.”

Salesperson: “I got some red, red roses. Got some pink, pink roses and white, white roses too.”

You: “No, ‘Radrazz’ roses.”

Salesperson: “Red raspberry roses?”

You: “No, I mean the roses that everyone in America is required by law to plant by the dozens in their yards every year.”

Salesperson: “Oh! I bet you mean ‘Knockout’ roses.”

You: “How dare you spell that wrong! I heard you! You pronounced it as one word. It’s two. ‘Knock Out.’ My lawyers will be sending you a letter!”

Salesperson: “If you don’t haul your fat behind off of my property right now, “knockout” will refer to your state of consciousness.”




  1. Jian duszka

    Bought 4 last year…cut them down to about 8 ” and they are behaving very well, not very thorny at all, i selected each one with that in mind, there were some that were really nasty. Buds already, cant wait. Did find rosette disease in the wild bushes on our property, we have cut as many as we could down to the ground, and will continue to mow them to ver. Sprayed them with roundup also. We will see what we will see.

    May 21, 2017 at 8:20 pm
  2. Stacie Johnson

    That’s insane! I bet you couldn’t even believe they would send something like that!

    May 21, 2017 at 9:26 am
  3. Nola

    I loved this!! Thank you for the great info and the laugh!

    May 13, 2017 at 2:44 pm
  4. Marta Duke

    I can’t wait to ask for “RADRAZZ” rose
    bushes at all my favorite garden centers!!!
    Your welcome…lol…

    April 24, 2017 at 5:33 pm
  5. Mary bordelon

    Thank you for the help and thanks for the laugh 😀😀

    April 24, 2017 at 12:22 pm
  6. Raye

    I so appreciate the info in pruning my knock out roses … and I especially appreciate the belly laugh I got on “what’s in a name!” Thank you for the info and the laugh! For someone with s name like Grumpy, you sure have a sense of humor!

    April 10, 2017 at 9:29 am
  7. Margaret Queen

    where are the answers to above questions?

    March 1, 2017 at 2:00 pm
  8. Christina Dykins

    Where can I find answers to the questions on your page please?

    January 22, 2017 at 10:26 am
  9. Christine R. W. Jennings

    I so enjoy reading your internet “column” on “The Daily South” part of “Southern Living”. Good advice and great laughs, too. Christine

    November 3, 2016 at 1:26 pm
  10. Lester

    Re: Leather gloves… Get a pair of welders gloves and you can survive most any rose bush, even Knock Out roses. Harbor Freight usually has 3 pairs of welders gloves for $10.

    November 1, 2016 at 10:19 pm
  11. Kathy Palmer

    My landscapers mistakenly trimmed my “mature” Knock Out roses all the way back to about 12-18 inches! Will they survive the winter and bloom again? I know spring is the time for a hard prune so I am so worried! We’ve already had one hard frost so know more are coming soon! What do you think???

    October 28, 2016 at 11:54 pm
  12. Howard Morgan

    I had Knock out roses that came down with Rose Rosette disease. Took them all out but 3 in the back yard. I cut them all the way back to the root stem. They came back the next year with no sign of Rose Rosette disease. That was 4 seasons ago. Still hearty and disease free.

    October 17, 2016 at 10:02 pm
  13. Theresa Carver Hudson

    Spray Garlic Barrier on them early in the season. Do it once a month after that. Bugs hate it and the roses and the leaves stay healthy! Garlic Barrier is a natural organic pesticide you can buy on line.

    October 6, 2016 at 11:04 pm
  14. Evie Fletcher

    Hahaha Thanks Grumpy. I live in North Carolina close to the Coast. So I should wait until late fall to prune my 3 plants whose name we shall not be spoken? 😂

    September 27, 2016 at 1:50 pm
  15. Kate

    Where are all the answers to the posts?

    September 25, 2016 at 8:35 pm
  16. Lillian Whitworth

    I thought when I purchased Knockout roses they would be disease free. Not so ! I have several that have a different looking branch and have been told that you must completely remove that rose and never plant one in that spot again. What is causing this problem?

    August 28, 2016 at 1:04 pm
  17. Trish

    Thanks for the info on pruning. My “whatever”(lol) rose bush has gotten quite tall and the bottom part got the dreaded black spot. So it looks, we’ll wrong. It’s currently in the resting phase. So I’ll cut it back quite alot. Again thaks for your info.

    July 18, 2016 at 6:09 pm
  18. Joan hughes

    Just purchased 4 knock out double reds for front landscaping. Directions say cutback every spring. Also says 3-4 ft high and wide. Please tell me they didn’t lie to me and I am going to be able to keep them 3-4 ft. The color is fantastic and a pleasing form. There are not a lot of thorns. I think I love them maybe, perhaps,might, hope . They are in the worlds worst soil, a misnomer, concretish clay, but I have back filled with garden soil. What I need to know is how short must I cut them back in the spring

    June 1, 2016 at 5:10 pm
  19. E.R. CORMIER


    June 1, 2016 at 12:12 pm
  20. Pat Whitworth

    I got 2 knockout rose bushes from a neighbor who had dug them up from his yard. I planted them even though they were not looking so good.. They are rather large so I cut them back but I think I need to cut them further back. The problem is that there are no buds to cut back to. Many of the stems are still green. Is it possible to save these bushes? How and where should I prune them?irish

    May 21, 2016 at 3:56 pm
  21. Theresa A

    Hello, i just planted two rose trees, i was told they are knockout roses. They are about three ft high with tons of blooms. I want them to get bigger and spread out. The problem is all the branches are twig size and im not sure how far back to trim to encourage faster growth. Anyone have advice? Should i trim or let branches grow?

    April 10, 2016 at 9:52 am
  22. Theresa A

    That was ama zing..

    April 10, 2016 at 9:46 am
  23. Steve Duff

    Pruning….say what!!! I try to ‘kill’ my Knock Out’s without success. They are sitting to close to my fence. I whack them all the way down and they continue to bloom and produce each year. They are indestructible. I just cut them way back because I need to have some fence repaired and they were in the way. We’ll see if I’ve done it this year. (Apr ’16 – St Louis area)

    April 7, 2016 at 10:54 am
  24. Marie

    I live in Florida SW. My knock outs look pathetic. Sparce blooms and very leggy. What can I do?

    March 5, 2016 at 8:55 am
  25. Brenda Blount

    God I’m so glad I found this site.
    I just trimmed 6ft. Knockout’s down to about 4ft tall.
    So now I’m stressing about do I need to put rose food on them or what? I think you’ve answered most of my questions. Thank you!

    March 4, 2016 at 2:00 pm
  26. Renee

    Can I prun my knock out roses now ?

    February 20, 2016 at 7:22 am
  27. Jackie

    Last year, my Knock Out rosebushes had bugs on them eating the leaves…so I sprinkled sevin dust on them. The bugs came back, though. What can you do…? They even ate the flowers.

    February 10, 2016 at 5:24 pm
  28. Daria McGeehan

    You must have a different plant or mine just hates me. We bought one as a trial and after 4 3 years the darn thing is not much bigger than when I bought it. Few blooms. My husband (he controls the yard) claims he is following care instructions to the letter, but I am not impressed. I want to try the heirloom varieties.

    February 8, 2016 at 1:36 pm
  29. Kristy

    Glad I ran up on this article! and BTW…I admire your sense of humor and style of writing! My knock out roses are two seasons old, and right now are about 5 ft tall! I was unsure about pruning, so I went to the Internet for answers and here I am! Hopefully my yard will have more beautiful Radrazz roses in the future!
    Thanks for the info!😃

    December 6, 2015 at 9:40 am
  30. Wheezy

    On Aug 29, Judy wrote about the large size of her plant. I’m no expert but my experience is that if you are willing to prune, and prune often and occasionally prune hard, you can keep your bush whatever size you want it to be.You aren’t going to kill your rosebush. Stuff wants to live.

    The Knock Out in the yard of my new place is tall and straggly. It needs pruning, and it needs more sun. It’s now December. The bush has dropped its leaves. I’ve got a nice new sharp pair of hand clippers and I’m going to cut the whole thing back to about 8 inches. Then I’m going to dig it up and move it to a sunnier location.

    By mid-summer I have no doubt it will be 4 ft high. If I want to change its size or shape, I will prune it. In the fall, if I want to change its size or shape, I will prune it. This isn’t rocket science. You can do it!

    December 5, 2015 at 10:42 am
  31. Hildie

    Loved your article w/your ‘zing’ sense of humor. Great dig. They deserved that.
    So I’ve always cut back to the first five leaf branch. You say cut back to an outward-facing bud. Not sure what that means.
    Also my grandmother always told me you can trim back roses 2/3 down in the Spring or Fall. She lived in Austria and had the most beautiful roses. Does/can this not apply to Radrazz? I live in VA and the weather is very similar to my grandmothers area.

    September 20, 2015 at 6:47 am
  32. lynn

    I had a friend ask my opinion of “Drop Dead” roses…”You know, the ones that say the bloom all summer?” OOOH, Knockout roses! Well, they are gorgeous!

    September 14, 2015 at 11:08 am
  33. Judy

    Living in the South “Knock Out” roses crêpe myrtles and Azalea bushes are very popular.
    I have huge knock out roses in my back yard for privacy around wood fence (fence beginning to gap).
    My question is this and more importantly when I
    Pruned them back I send hedge clippers⁉️⁉️😁
    When they started to grow back OMG hey grew
    Monstrous size stems in big clump size that were so heavy I had to literally cut off! It looked like a wedding bouquet.
    It’s now the end of August I’m just getting back in town and I know they r at least 7ft. Tall I’m 4″11
    Please tell me what to do!!! I need help!!!!!
    Thanks anybody And everybody 😂

    August 29, 2015 at 3:47 am
  34. A Better Rose Than Knock Out | Southern Living Blog

    […] Pruning ‘Knock Out’ Rose — When, Why, and How […]

    July 30, 2015 at 10:00 am
  35. Lori

    My Knock Out came down with a nasty case of Rose Rosette disease, and I yanked it out of the flower bed faster than a bored attorney can send a hateful letter. I have read several places where the red ones are susceptible to this disease, but then, I read something else that says they are not, and they are the best thing since sliced bread. Well, sliced bread or not, I will not have one. It is tragic too because they do bloom nicely and are easily maintained.

    March 30, 2015 at 3:44 pm
  36. Dea

    I haven’t tried the Knock Out (notice that I spelled it right! No need for lawyers here!) rose yet. I love antiques and have a couple of Dame de Coeur and an Earth Kind called Belinda’s Dream. Both of those have thorns on them that not only will go right through leather gloves, but will actually ambush you and ravage anything within striking distance. But they do produce some gorgeous flowers, and they’re not very susceptible to disease or bugs either. BTW, I was always told that roses should be pruned on Valentine’s Day, and have always used that as a guide.

    March 27, 2015 at 9:44 pm
  37. Margaret

    And here I thought it was my not being attentive enough to my Joseph’s Coat. It certainly does attract black spot

    March 27, 2015 at 3:38 pm
  38. Carolyn

    Steve, as a fan and old proofreader, I think you mean “A resting phase is a good time to PRUNE,” not “A resting phase is a good time to bloom,” as the article says.

    March 27, 2015 at 10:53 am
  39. Teeta Sawyer-Simmons

    Thank you, mine are huge and I thought they would have stayed small. Mine are about 7 foot, not kidding. Trimmed one last year and you aren’t lying about their nasty thorns!

    March 26, 2015 at 7:44 pm
  40. Kathleen

    Knock Out’s a great rose, but like other overused plants, it’s become a cliche’ fixture in every yard. But that’s better than seeing no roses at all.
    I struggle to grow “Joseph’s Coat” which is beautiful & NOT a cliche’ rose, but it’s not overused for a reason. It’s a natural magnet for blackspot here.

    March 26, 2015 at 10:24 am

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