Summertime care for Knockout roses

Knockout Roses and summertime maintenance.

Over the last few years nothing has affected the color of our landscape like the Knockout rose.  Originally this rose was praised as “maintenance free” (and it is, to a point) but we have learned that there are certain tricks to getting the most out of the plant.  Read on—

Beautiful flowers on a Knockout rose, but the spring flush is starting to fade.

Beautiful flowers on a Knockout rose, but the spring flush is starting to fade.

After over 30 years as a landscaper and plant grower, I have learned that there is no such thing as “no maintenance”, only “low maintenance.” The Knockout rose is definitely in the low maintenance category.  After the first beautiful flush of bloom, the plant begins to fade.  This is because the first blooms have been pollinated and the plant is busy with its inherited job of making seeds.  This shows up as dead blooms and an overall dropping of the early spring petals.

The seed pods develop and the petals fall.

The seed pods develop and the petals fall.

Here’s what is going on.  The flowers have been pollinated and are in the process of making seed pods.  There is a chemical produced in the plant that slows down the next blooms so that the seed pods can mature.  In order to fool the plant that it needs to make more flowers, the seed pods must be removed.  This is called “deadheading.” All serious flower growers know about deadheading and I talked to Judy about her Knockout roses the other day about it.  Judy said that cutting off each spent bloom took a lot of time and trouble.  It started me thinking about the best way to accomplish the job.

My feeling on the deadheading job on the roses (and the way I do it on the job) is to combine the job of deadheading and cosmetic pruning into one operation.  I start by looking down into the plant to isolate the stems which have mostly spent blooms.

Look inside the plant to isolate the stems with spent blooms

Look inside the plant to isolate the stems with spent blooms

In performing my task, I am trying to promote new growth and more flowers.  I want to be careful to leave any new growth which looks like this:

Careful pruning and deadheading will produce new growth like this--with lots of flowers.

Careful pruning and deadheading will produce new growth like this–with lots of flowers.

If I reach inside the plant and cut the stem (directly above a new leaf node) I can not only get the plant deadheaded in less time but also cause the stem to branch out and make even more flowers than before.  You may read about some of the principles of pruning in this article onhow to prune a jade plant.”  The principle is the same. I carefully cut a stem in a manner that performs two tasks.  Here is what I cut.

deadheading and pruning the Knockout rose at the same time.

deadheading and pruning the Knockout rose at the same time.

After this cutting, the old stem will branch out and form new growth which will develop more flowers and will, again, look like this:

New growth on the Knockout rose

New growth on the Knockout rose

The process is really rather simple and you probably won’t mess up.  You can cut the stem short and get more branching at the top of the plant or you may wish to take out a larger cutting which will let more light inside the plant and increase the later flowering even more. You may wish to try deadheading on all of your flowers, especially marigolds and petunias. It does make a difference in the number of flowers you will get.

An application of a high phosphorous plant food or fertilizer will also help the plant to flourish and produce even more flowers.  Maybe use something with an analysis of 15-30-15 or a similar ratio.  Liquid feeds are fine and it doesn’t hurt to pour it all over the leaves as well as around the roots.  The upside for liquid is that it works faster.  The downside is that it doesn’t last as long.

Time release fertilizers such as Shake ‘n Feed or Osmocote will work well and last the entire season.  You need to scratch these into the soil or pour them into a small trench around the plant for full effect.

Time release fertilizers break down slowly and feed for the entire season

Time release fertilizers break down slowly and feed for the entire season

You may wish to read my article on fertilizer here.

Another article on pruning Knockout roses

And an article on pruning crape myrtles is here.

Every now and then you may get fungus on the roses, and sometimes aphids will set in.  I suggest a combination fungicide/insecticide which you can purchase at any good nursery.

Got Questions?  Enter a comment.  I always try to answer.

I try to put up a new article every Sunday. Stay in touch.  Share it with your friends.

If you live in or around the northwest Georgia area and would like to have a consultation on your property with johntheplantman, you may contact John Schulz by email at .  Do not send pictures or attachments as they will be deleted.

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16 Comments (+add yours?)

  1. Jane Schulz
    May 15, 2010 @ 18:56:04

    John, I love my knockout roses and am serious about deadheading. I learned about that from my pansies. I thought it just meant that they “loved to be cut.” Anyway, my knockout roses give and give, as long as you cut them. How easy is that?


  2. Marion McAbee
    May 16, 2010 @ 20:20:41

    John, thanks for the info on pruning. I was already about half way there when I didn’t have the time for deadheading and found it easier to bite further down on the stalk to get more of them at one time. What I was guilty about was actually helping. Thanks, also, for the crepe connection and Bill’s comments on knife handles and walking staffs. Tomorrow, I will check if I have some good straight sections to cut out and maybe try carving some wood spirits for the grandkid’s interest. Up here in North Georgia, we still have our fair amount of “Crepe Murder” going on and it is good to be reminded of the correct method.


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  5. Ronda
    May 09, 2011 @ 13:09:59

    Thank you for this information! I was wondering how come my roses stopped blooming! Now I know and have cut back the old blossoms/seed pods and stems appropriately…


  6. Agatha
    May 24, 2011 @ 07:09:06

    I am a first time gardener and my new knockout rose had a tree branch fall on it. The blooms sputtered and I thought the bush was toast but saw new growth. I am going to carefully deadhead them that save it, thanks for the how-to info.


  7. Mona Pyatt
    Jul 13, 2014 @ 15:03:58

    Thank you so much! This is the best article I have found on Knockout roses! I was doing the right thing, but most articles told me I did not need to deadhead….I want the most out of these rose bushes and now I think I will!


    • John Schulz
      Jul 13, 2014 @ 15:41:24

      Thank you, Mona. It makes me feel good to know I was helpful. I have written a lot of articles on pruning. The “search” block on the blog will direct you. The more you prune the roses the more flowers you will get. They bloom in cycles.


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  14. paula
    Jun 09, 2015 @ 17:16:51

    I’ve been searching for over an hour to find some pertinent info on why my knockouts quit blooming….THANK YOU so much for this article! I actually started to deadhead them, but stopped, thinking I might do damage, but I’m going back out now to get it done! >sidenote: I had been smashing an over ripe banana into the base of my rose bushes during the winter months, and it seemed to really make them happy and lush when they finally came to life this spring. Have you heard of using bananas on roses before?


    • John P.Schulz
      Jun 09, 2015 @ 17:28:14

      Thanks for writing, Paula. I hadn’t actually heard about the bananas but they are a wonderful source of potassium which is the third number in the sequence on the fertilizer bag. 8-10-10, for instance, would signify 8% nitrogen, 10% phosphorous, and 10% potassium.


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