Rosa ‘Knock Out’
While David Austin may have set the standard for modern rose growers, Knock Out roses totally changed the landscape.
Those of you who remember gardens in the ‘80s know that roses had fallen out of favor. People saw them (justifiably, sometimes) as fussy, difficult, and ridiculously tender.
You’d be most likely to find them in your grandma’s garden, and unless she was a talented or dedicated gardener, the shrubs were usually covered in aphids and powdery mildew.
Most of them bloomed once for a short time and then needed deadheading to return the next year. Until they came back, you had a fairly boring plant that didn’t add much to the yard.
Then, along came Knock Outs. Suddenly, people who couldn’t grow a rose to save their life could have big, beautiful plants that bloomed all summer long and needed hardly any maintenance.
It’s hard to overstate how much of an impact this line of cultivars has had on the modern rose market.
If you are looking to grow one in your yard or you’re just curious about where they came from and what sets them apart, this guide has you covered.
Where Did Knockouts Come From?
Many of the roses we know and love today were bred by horticulturalists or scientists. However, some of the most successful breeds of all time were bred by a hobbyist with no technical training.
Will Radler fell in love with roses while reading a Jackson & Perkins catalog in the 1950s.
At just nine years old, he was cognizant of the fact that while his grandpa had the catalog, he didn’t grow roses in his own garden.
Radler convinced his family to buy him a rose plant, but he quickly discovered that he was the only one his age who seemed to share his passion.
At the time, these plants were considered fussy and old-fashioned, but Radler didn’t give up on them just because his friends and family didn’t share his interest.
He maintained his interest through college and beyond, when he worked at the Milwaukee County Parks Department. In 1974, he started his rose breeding adventures in his basement.
After over a decade of work, Radler finally unlocked the code to commercial success with “89-20.1,” which turned out to be a hardy, long-blooming, disease-resistant shrub with pinkish-red blossoms. He eventually named it “Radrazz.”
Star Roses and Plants in Philadelphia took a chance on the new creation and started selling it in 2000. Right away, it was a massive success with gardeners.
Since it was introduced commercially, nearly a billion of the shrubs have been sold in stores across the country, including big box retailers like Lowe’s and Home Depot, and many other colors, along with one miniature, have been introduced.
Both Radler and Buck felt that if a plant is too difficult to grow, people simply won’t grow it anymore, and they used this as a guiding principle.
Buck made some cultivars that were just as hardy and resistant to pests, but Radler found the magic combination that made even the most stubborn growers change their minds.
Today, he continues his efforts, trying to bring new options like spotted and purple roses to the market, two features that have eluded breeders.
The Benefits and Drawbacks
Knockouts can grow in places where most people would never have dreamed of planting a rose in the past.
If you suggested planting an Old World cultivar in a parking strip 50 years ago, you would have been laughed out of the room. But parking strips and other arid areas are no challenge for the Knock Outs.
Gardeners wouldn’t have dreamed of putting roses in parks and commercial raised planters back in the day either, but now they’re a common sight at shopping malls and in schoolyards.
They’re simply low-maintenance, disease-, and drought-resistant enough that you can place them where other types would falter.
If you’ve always wanted a rose bush but you’ve hesitated because you’ve heard they’re fussy, this series of cultivars may convert you.
On top of their toughness, they’re self-cleaning—which means you don’t need to deadhead them—and they bloom all season long. They also don’t require any complex pruning and need far less fertilizer than some other types.
All that said, some purists feel Knock Outs aren’t worthy of the name Rosa. They argue that roses should be a bit fussy, and that’s what sets them apart from other flowers.
“Real” roses, they say, have a pleasing fragrance, long stems, and breathtaking blossoms. These flowers have little, if any, fragrance, short stems, and are admittedly simple.
While critics say Knock Outs don’t have any scent, they do actually produce an extremely subtle, sweet fragrance. While it isn’t characteristically rose-scented, it’s certainly pleasant, if a bit mild.
The success of Knock Outs has also made it difficult for people who want something old-fashioned to locate a classic cultivar, since many big box stores and nurseries prefer to keep these hardy best-sellers in stock.
Additionally, these roses tend to dominate gardens across North America. Not only do these two facts mean we are losing plants that have been around for decades, but a lack of biodiversity is never a good thing.
Meet the Family: Cultivars to Select
The Knock Out family is constantly growing. As of today, these are the cultivars that are available commercially:
You have one guess to figure out what makes this particular plant stand out. Did you say that it might have red flowers? You got it!
‘Radrazz’ is the original and features cherry-reddish to hot pink petals on single blossoms. This plant can grow up to four feet tall and wide and is hardy down to Zone 5a.
‘Radcon’ is just like the red cultivar, except, of course, the petals are pink. This isn’t a shy, retiring pink, either. The flowers are bright and bold.
Knock Outs are sometimes criticized as having flowers that are too simple and small. While not everyone needs or wants big, fully double, frilly blossoms, those who want something a little fuller can turn to the double option.
These shrubs come in red (known as’ Radtko ’) or pink (called’ Radtkopink ’) with double flowers.
Each flower has about 20 petals, making them fuller than their cousins. For reference, roses can have as few as four petals each, while some very full double flowers can have 100 or more.
They reach about four feet tall and wide at maturity, are slightly cold hardier than the red and pink originals, and grow well down to Zone 4b.
Beautiful Rainbow, or “Radcor,” has bright orangish-pink blossoms with a bright yellow center. The foliage is deep, dark green all summer long, but it emerges bronze in the spring, adding to the seasonal interest.
Additionally, the plant has an extremely compact growth habit, even more so than the rest of its family.
Even still, it grows to the same four-by-four size that most others do. In other words, the branches and leaves grow more closely together, giving the plant a more dense appearance despite being the same size as its cousins.
It can be planted in gardens down to Zone 4a.
The “blushing” Knock Out ‘Radyod’ starts out medium pink before fading to pale pink.
It features the same four-foot-tall and wide growth habit as its friends, but the foliage has a distinct blue hue that helps it stand out. It’s always nice to offer something special that your siblings don’t have, right?
Slightly larger than the rest of the bunch, ‘Radral’ grows to four and a half feet tall and wide with matte, medium green leaves.
But that’s not what makes it special. The brick orange blossoms start out bold and bright before fading to a pleasant coral color as they mature.