Knock Out Roses Are a Gardener’s Dream Come True

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Discover the fascinating story about how Knock Out roses became the original and most popular low maintenance rose to grow.

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
The addition of Coral Knock Out roses brought more vibrant color to the popular series.

Caring for roses was once an art form, including fastidious pruning, spraying for diseases and pests, and wrapping in winter. While some gardeners are still committed to the craft, Knock Out roses are a better option for low-maintenance gardeners. Their development marked a shift in what roses can be. Tough as the thorns adorning their stems, Knock Outs boast luscious, well-rounded foliage and flowers that just can’t quit. To fully understand how Knock Outs were produced, it’s helpful to know a few things about William Radler, their creator.

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An Idea Arose for a Better Rose

Will Radler, Inventor Of The Knockout Rose, Walks Through His Test Garden In Greenfield, Wi In July Of 2019.Sara Stathas
Will Radler, inventor of the Knockout Rose, walks through his test garden in Greenfield, Wisconsin.

As a child, William—who prefers to be called Will—spent time with his siblings at his grandparents’ house, where they had to make their own fun. The home was relatively devoid of entertainment for children, with the exception of a few National Geographic magazines and a rose catalog. He would flip through the catalog’s pages, drawn to the elegant cultivars, naming them as he went.

Will Radler, Inventor Of The Knockout Rose, Sits On A Bench In His Test Garden In Greenfield, Wi In July Of 2019.Sara Stathas
Will Radler

Decades later, he served as director of Boerner Botanical Gardens in Hales Corners, Wisconsin, while carefully and deliberately crossbreeding large plots of roses in his own yard. Will dreamed of an even more vigorous rose, one that didn’t need pesticides or constant attention. “Everything I learned about roses told me that producing a rose like the Knock Out was possible. Probable? No. Possible? Perhaps.”

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Nosy Neighbor Gives Approval

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Original Knock Out rose

Through the 1980s, Will bred prolific bloomers—shrubs with perfect growth habits and crosses that could take just about everything but the kitchen sink. Eventually, he discovered a plant that hit every single mark. “It had this well-rounded shape with perfect foliage that didn’t get diseased,” Will says. “When it started blooming, it just kept blooming and blooming. Even in the fall, when the rest of the roses started looking tired, Knock Out didn’t.”

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Double Knock Out rose

The testament to this discovery came when a particularly persnickety neighbor walked up to his front porch. According to Will, this was a common occurrence—she always had a piece of unsolicited advice or less-than-constructive criticism. He opened the door, and she pointed her finger at a particular rose bush and said, “You know, if you could produce more roses like that—you would really have something.”

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Peachy Knock Out rose

Shocked by the positive comment, Will realized he had created something special. The next concern was whether the average gardener—the person he felt would benefit most from the Knock Out—would like it.

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Knocking Out the Rose World

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Pink Knock Out rose

“I didn’t even know if I’d be able to get it into the market for sales,” Will says. He added that when it was released in 2000, rose breeders were working on scarlet red roses, while the original Knock Out was red but as close to purple as possible. But it sold. Sales improved yearly, defying the crash most roses see after being on shelves for a few springs. It certainly deserved the hype.

Knock Out Rose Care

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Sunny Knock Out rose

Knock Out roses routinely grace best-of and top 10 lists because they bloom from June to frost, are especially resistant to black spot, do better than others in part shade, and withstand winter in most regions without bulky insulation. Will’s Knock Outs come in many varieties with both single and double petals, and range from cherry red and vibrant pink to creamy yellow and pure white.

Knock Out roses are well suited for growing zones 4 to 11, and perform best when planted in full sun and well draining soil.

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Rosy Future Outlook

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Rainbow Knock Out rose

Will hasn’t slowed down—he still breeds and tests roses at his home. He’s working on the usual suspects: bright new colors, more disease and pest resistance, and increasing the scent of the blooms—that’s something critics say is more subdued in Knock Outs than in traditional roses.

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
Orchid romance rose

But Will has something bigger up his sleeve. “I would really like to produce the first rose with full-season interest,” he says. He’d like to see a specimen with colorful, thornless canes in autumn and bright fruit that lasts through winter for birds or dried bouquets. When asked what rose traditionalists may think of a thornless rose, he answered quickly: “I don’t care.” His roses are for everyone, he says, not just gardeners with a static idea of what roses can be. “I may be taken as a dreamer,” Will admits.

Knock Out Rose Variety From Will Radler’s Test Garden In July 2019.Sara Stathas
Fruity Petals rose

But he believes that if you don’t have big dreams, you’re not going to see the rewards. His dream may not be that far away. I talked to Will on a cold November day, just after the first snow of the season. He led me outside to his test gardens and pointed to a frosty thornless rose bush. Will says, “While Knock Out made a major breakthrough in what people want, it isn’t the end of the line.”

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Rose Boot Camp

A Variety Of The Knock Out Rose Taken From Will Radler's Test Garden In July Of 2019.Sara Stathas
White Knock Out rose

Life isn’t a bed of roses for the plants grown in Will Radler’s test gardens. After seedlings go through an intense review in his basement workshop, a lucky few get planted in the test garden, affectionately called the boot camp. Young bushes are planted close to each other to encourage disease, and they’re generally mishandled. They’re watered from overhead around dusk (typically a no-no) and diseased leaves are saved, ground up and sprinkled on healthy plants routinely. The abuse is purposeful. Many roses meet their end in a trash pile, but the best plants receive more testing and may even make it to a grower.

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Where to Buy Knock Out Roses

flowers for pots, Petite Knockout ContainerStar® Roses and Plants
Petite Knock Out Rose

Knock Out roses are available at garden centers nationwide and are sold online at many retailers including The Home Depot and Nature Hills Nursery. One of the newest varieties to grow is the Petite Knock Out rose. This bushy, flowering plant grows to a maximum height of 18 inches, making it the perfect size to place in a container. The bright red blooms are long lasting and the plant is just as tough as its larger Knock Out rose cousins.

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Rachel Maidl
Rachel Maidl is a senior editor for Birds & Blooms magazine. She enjoys bird-watching in her urban backyard and local state parks, gardening for pollinators and researching new plants. Her favorite backyard visitors are the bumblebees that visit her sedums.