William Radler,72, owner of Rose Innovations, LLC, in Greenfield, WI., with his original Knockout Rose he developed in his basement. (Jack Orton/For The Washington Post)

Will Radler was still just an amateur rose breeder — a basement hobbyist, really — when he walked out of his home in Milwaukee carrying that fateful baby rose in a soil-stuffed cup.

He didn’t realize it then, back in 1989, but he held in his hands a flower with such remarkable qualities that it would grow to be the bestselling garden rose in the country. His creation is credited with reversing the sagging fortunes of the difficult garden queen. Radler’s rose is so hardy and requires so little care that it can be planted in places once unimaginable — road medians, mall parking lots, ignored gardens.

It’s a good bet that any dense bloom of roses in a surprising spot — and roses are at peak bloom right now — can be traced back to Radler’s flower.

“Some things are just too good to be true, but this was an exception,” said Craig Reiland of the American Rose Society, which has stood as the flower’s governing body for more than a century.

Radler’s rose is called the Knock Out. It changed the entire rose industry by emphasizing low-maintenance. It still dominates the market. And it made him a very wealthy man. But his story is not widely known outside the small world of fellow rosarians. Now, at 72, he continues to invent new rose varieties. But he has faced a backlash, as some believe Knock Out’s success has come at the expense of classic roses, as well as criticism — perhaps none more infuriating to Radler than the allegation that his rose has no smell. And this cuts to the heart of the doubt about what he created.

After all, what kind of rose is this?

The rose’s reputation for being fussy is part of its charm, traditionalists argue. Roses require constant pruning, watering, chemical spraying. Even in mild winters, they need to be covered just so. The reward for all that hard work is a stunning flower with lush petals and distinct aroma. This is what makes a rose a rose — what poet Rainer Rilke called “oh pure contradiction.”

But over the years, fewer people have wanted to expend the effort. Other flowers demanded less.

This was clear to Radler even as a young boy in the 1950s, when he stumbled on his passion for roses while thumbing through the Jackson & Perkins rose catalogue at his grandparent’s house. He noticed his grandpa had never bothered to plant roses. At 9, Radler persuaded his parents to allow him to plant a rose bush. And he quickly saw that all the other rose fans were old. Roses were a fading passion even then, increasingly restricted to the flower shop.

Radler believed the problem was the rose had been overbred for beauty. The modern rose had transformed from just five petals and once-a-year blooms to dozens of petals — hundreds even — and multiple blooms. But this tinkering also made the flower fragile, like a sickly award-winning dog.

Radler wanted to make roses easier.

“Fixing roses was one of my first goals,” he recalled.

Others had dreamed of it before. Plenty of new rose breeds have hit the market over the years promising to be disease-resistant or easy-care. But the hype never lived up to performance.

“The plant is supposed to work for you, not the other way around,” said Ping Lim, a rose breeder in San Diego who has known Radler for decades. “The rose had to change. That’s the only future it had.”

After college, Radler went to work for Milwaukee’s county parks department, where he ran the botanical gardens and immersed himself in the rose world. In 1974, he started breeding roses in his basement. It was easy. He just played the part of a bee, spreading pollen between parent plants to achieve the desired mix of traits.

But he had to be patient, too. Success or failure revealed itself only in the summer, after he moved seedlings from his basement lab to his backyard garden and waited to see what happened.

It took 15 years before he carried out a rose with a white inventory tag plunged into the soil reading “89-20.1.” A few weeks later, a next-door neighbor, accustomed to seeing an assortment of failing roses in Radler’s backyard, pointed to one stunning bloom.

“You know,” Radler recalled her saying, “if you could produce more roses like that one, you’d probably be onto something.”

The rose was special, a dense bush full of pinkish-red blooms. No need to prune. Dead flowers just fell off. No need to spray. The rose appeared immune to diseases such as black spot mildew. And Radler’s roses just kept popping out all summer long.

His first shot at the big time came when a wholesale nursery agreed to give his rose a trial run. Wholesalers clone specimens for several years to see how they perform. Only the best are ever sold to the public.

Star Roses and Plants, outside Philadelphia, worked with Radler’s rose for eight years. Chief executive Steve Hutton said Radler had turned traditional rose breeding on its head by targeting disease resistance before appearance.

“That was his genius,” Hutton said.

Star Roses started selling Radler’s plant in 2000. They gave it the name Knock Out. They filed a patent, which became useful for fending off the many imitators. And it was honored with a prestigious All-American Rose Selection.

But Radler had no clue if the Knock Out would sell. He was warned that new rose sales typically peaked in the first year, like a blockbuster movie on opening weekend. He would earn a royalty on each rose plant sold.

His royalty check that first year was $60,000.

The next check was for significantly more than that. And so was every annual check that followed. This was unprecedented. Sales of Knock Out have flattened out only in the past year, Radler said, as the breed fell to No. 2 among rose plants. But the top spot still belongs Radler, thanks to his Double Knock Out — an easy-care rose with more petals. He has four more varieties of Knock Out on the market.

More than 90 million of Radler’s roses have been sold, Hutton said.

Knock Out roses are the top-seller at box stores like Home Depot and Lowe’s, according to those chains, and smaller garden centers like Merrifield in northern Virginia.

“It’s truly changed the industry,” said David Yost, who works in Merrifield’s plant clinic.

Yost said it’s clear consumers prefer easy-care roses — either Knock Out or other brands — and that has made the thousands of other named rose varieties harder, if not impossible to find. While Knock Out has been good for the rose market overall, he said, not all roses have benefited.

“Nobody wants what our parents had — the hybrid teas, the classic roses of that day,” Yost said.

That leads to one major complaint about the Knock Out.

“Not everyone accepts it as being a rose,” said Reiland of the American Rose Society.

He thinks it qualifies, even if it lacks the classic long-stemmed elegance. Reiland said Knock Out has other attributes. Back when he worked for the city of Tyler, Tex., Reiland planted Knock Outs along street medians. It was a gift of beauty. He would never do that with any other kind of rose.

“They did really well,” he said.

Other growers have noticed the Knock Out is susceptible to rose rosette disease, which is spread by a microscopic mite. And the problem, once rare, has been worsened by Knock Out’s popularity as a mass planting. Merrifield’s Yost said he worried about a lack of floral diversity given Knock Out’s dominance.

But the biggest knock against the Knock Out is the lack of smell. Aroma is a favored rose trait. Breeders aim for it. Some gardeners are upset to find the smell missing.

This is the criticism that upsets Radler the most.

“It is fragrant,” he said. “The problem is everybody insists that there’s only one fragrance in a rose. But there are many smells.”

To him, the Knock Out smells delicate, fruity and sweet.

Radler now has a small staff to help him breed roses in his basement. He’s bounding with ideas. Recently, he was inspired by a brilliant example of an orange-red rose with white spots during a trip to France.

“There’s no reason we can’t have spotted roses,” he said.

So he might work on that. He talked about breeding roses with mahogany-colored leaves, Knock Out hybrid tea roses, orange Knock Outs, purple ones, too.

“Can you imagine?” he asked. “Why can’t we have that?”

Maybe even a Knock Out with a fragrance unmistakable as belonging to that flower named the rose.