This month's meeting of the Golden Spades covered a topic that Homestead Education Coordinator Gene Sumi gets questions about all the time, he says, so often that he decided they needed their own meeting to answer all the questions.  So here goes.

How Knockout Roses Came to Be

Knockouts are the pride and joy of the rose-lover who bred them and put them on the market, after which event they were soon chosen as an All-American Rose Selection and became one of the most popular plants in the U.S.  That breeder is William Radner, whose fascination with roses began when he was just 9 years old.  He bought his first rose for just 49 cents and joined the local rose society when he was a teenager.  So he loved roses but had a complaint - they required too much work.  They weren't cold-enough enough for his Wisconsin garden, so required winter protection, a chore he didn't love.  Not to mention that they got fungal disease and had to be sprayed every two weeks! 

So Radner started his life-long quest to, in his words, "breed the maintenance out of roses" so they'd be easier for the gardener AND better for the environment, since a disease-resistant plant could be pesticide-free. 

Above, William Radner and Knockouts growing at the Morris Arboretum

Above, William Radner and Knockouts growing at the Morris Arboretum

The first Knockouts were a semi-double red, though now they come in a variety of colors and with either single or double flowers.  Unlike the long-stemmed hybrid tea roses grown for cut flowers, Knockouts are shrubby in form, with flowers in large clusters.  They're easier to incorporate into borders and can be used on their own in even the most difficult spot - like the median strip along 16th Street in Washington, D.C., where they're known to thrive.

Knockouts famously bloom throughout the season, right up until December in our typical year.   Customers often ask Gene about the extra height they notice on the Knockouts in  their garden - over 5 feet tall, more than the 4 feet indicated on the label.  His answer is that with the right soil, fertilizer and a bit more sun, don't be surprised to find them hitting the 5-foot mark.

Disease-Free? Mostly

In order to select for roses that could resist fungal diseases like blackspot, Radner collected diseased petals from roses, sprayed them on the varieties he was trying out, waited two weeks and kept only the healthy-looking ones.  Since most roses are blackspot-magnets, few passed this test.  The result was a rose that is largely safe from fungal disease, though not entirely, depending on the weather.

Asked what to do if you DO have roses with blackspot, Gene recommends spraying with copper, Daconil or a contact pesticide every two weeks - that's the traditional treatment - or for the low-maintenance gardener, spraying every six weeks with the new systemic fungicides with Tebuconazole from Bayer or Bonide, both of which work quite well.

But there are other rose diseases, and 2011 and 2012 saw an unusual amount of Rose Rosette Disease here in the East, occurring on not all roses but seemingly haphazardly, on some.  The only "remedy" is to get rid of the plant in its entirety, then wait two years before growing another rose in that spot.  Even some examples of the super-tough 'New Dawn' climbing rose fell victim to this destructive disease in the last two years.  And even a few Knockouts.  

Asked about Japanese beetles, Gene recommends just not worrying about them.  They're only here about five weeks.


Knocks bloom in cycles, a succession of five throughout the season here in Maryland.  After each bloom they rest and shore their resources to bloom again and that's when they benefit from a good feeding - just after they bloom.  Gene told us that like blooming annuals, roses are almost impossible to overfeed, especially with a good organic fertilizer like Rosetone.  

Another good fertilizer for roses is Osmocote, which can be sprinkled on top of soil and lasts for months.  It makes nutrients available when the plants need those nutrients - cool!

Begin feeding after the leaves have appeared (not now but in March) with a slow-release fertilizer; it'll be there when the plant needs it in April.  If you prefer a water-soluble fertilizer like Miracle-Gro, wait until the plant has gone through a full bloom cycle before applying.  And stop fertilizing by the end of July or early August when the plants are preparing to go into dormancy, so not a good time to push them to produce new growth.  

One Golden Spades member told us he uses Bayer First Advance for the first feeding of the year, then Osmocote just once per season.  

Knockouts at the Morris Arboretum

Knockouts at the Morris Arboretum

Soil Test Tip

If you haven't had the soil around your Knockouts tested now's a good time to get that done.  Gene likes the University of Delaware test, which can be found here online. 


While not requiring pruning to shrive, Knockouts can be pruned and respond quite well to it.  You can give them a light pruning with hedge shears or hand pruners to a height of three feet after any of the blooms fade, or one heavier pruning to a shorter height just once a year, in March, as the leaves are bursting out.

BUT don't prune at all the first year your Knockouts are in your garden.  Start pruning in their second season.

The dreaded "3 Ds" from pruning basics can be removed at any time - that means branches that are dead, damaged, or dysfunctional.  Dysfunctional means it's growing in a bad spot or in the wrong direction, maybe toward the inside of the plant, or it causes two branches to rub against each other.  Click here for more pruning help from Star Roses and Plants.

Knockout Roses in downtown Annapolis

 Knockouts in downtown Annapolis


Knockouts don't really need deadheading (removal of faded flowers) at all because they self-clean, dropping their faded flowers to the ground.  Still, one member reported that he's getting more bloom cycles from his Knockouts, thanks to deadheading.  And this is the same member who'd carefully studied how the plants responded to fertilizers of various types at various times, so I might just follow his advice.  Can't hurt!

Knockouts may not be maintenance-free (what IS?) but they're truly easy and with the great choice of colors available now, what's not to love?  Below are some Knockouts I noticed surrounding on the South Lawn of the White House, blooming like crazy in mid-October.

Knockout Roses at the White House

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