The rose that conquered the world

Double Knock Out rose - Star Roses/Conard-Pyle

Double Knock Out rose - Star Roses/Conard-Pyle

We love roses – their gorgeous form, their sumptuous scents and their storied history. We hate roses – the Japanese beetles, the black spot and the bloody business of dealing with those wicked thorns.

In the buggy, humid Northeast, no flower raises more anticipation or causes more heartache than the average rose. I personally have dug up and given away (or simply discarded) more roses than I care to mention.

Things have changed in first decade of the 21st century with the debut of the modern, bullet-proof shrub rose. None is more famous than ‘Knock Out,’ this year celebrating 16 years of phenomenal popularity. It has become the most widely planted rose in North America – more than 90 million have been sold as of last year.

Introduced in 2000, ‘Knock Out’ caught on in a big way by growing vigorously,  dropping spent flowers cleanly and quickly reblooming, all summer long. Even more miraculously, it was neither defoliated by black spot nor particularly favored by Japanese beetles. It wasn’t a classic hybrid tea, which many think of as rose perfection, but it was practically fool-proof and it gave fresh hope to discouraged rose lovers.

The truly intriguing thing about this break-through rose was that it was produced not by a big commercial breeding operation, but by a man for whom creating roses was a hobby. Roses were a lifelong obsession, maybe, but strictly a spare time preoccupation for Bill Radler, former director of the Boerner Botanical Gardens in Hales Corner, Wisconsin.

I interviewed Radler a while back at his Wisconsin home and learned something else: ‘Knock Out’ was the rose that almost wasn’t. Radler, who admits to having “some version of a photographic memory,” can still see sequence of events in his mind’s eye.

“Unlike hundreds of other seedlings I raised, Rose 8920.1 never flowered inside under lights,” he says. “It was the runt that wouldn’t bloom, and there came a point when I tossed it on the discard pile. I can’t say exactly why, but the next day I pulled it off and planted it,” he adds. “This was the one that became the wonder rose ‘Knock Out.’”

There you have it: Breeding a better rose takes infinite patience, serious drive – and a bit of luck.

“Sometimes, it’s all a crap shoot,” Radler admits.

It’s possible that a commercial breeder would never have bothered with so ornery a rose. New roses are conceived when a breeder fertilizes or “crosses” a female setter of hips with a male producer of pollen. The “mom” of ‘Knock Out’ was a “reluctant female,” generating as few as three seeds per hip instead of the normal 30 or more.

When he couldn’t get some of his early seedlings to set any hips at all, Radler had to rethink. He usually made his crosses early in the morning when flowers had just opened but before the bees were active. Then he noticed that some of his hybrid plants didn’t actually open until noon.

Using these flowers and shifting his work to afternoon, he finally saw success – three seedlings from his first batch, three from the second, but 30 or 40 as he perfected his technique. Born from the same “father” (RADDAD) and “mother” (RADMOM), they are all siblings and all variations on ‘Knock Out’ or ‘Double Knock Out.’

The original 'Knock Out' in a garden setting - Conard-Pyle

The original 'Knock Out' in a garden setting - Conard-Pyle

Not all sibs are created equal, and Radler will only claim Japanese beetle resistance for ‘Knock Out,’ ‘Pink Knock Out’ and ‘Blushing Knock Out,’ three of seven roses in the series. Identifying roses with traits good enough to join the ‘Knock Out’ family is a matter of growing thousands of roses, throwing every obstacle in their way and selecting winners from the survivors.

To find plants immune to black spot, Radler makes a slurry of diseased leaves and inoculates the plants. To identify Japanese beetle resistance, roses are grown in heavily infested locations. Cold hardiness? He’s growing in Wisconsin, which gets pretty darn cold, and offers the plants no special protection.

Growing, testing, evaluation and propagation continue over the long haul. It took nearly 16 years to get the original ‘Knock Out’ on the market. Conard-Pyle, a major nursery grower, became involved in production and sales, and has introduced every Knock Out rose in the series under its Star Roses brand.

By 2000, when ‘Knock Out’ was named as an All-America Rose Selection, there were at least 250,000 roses ready for sale. By now, it is the top-selling rose not just in the country, but in the world, Radler says. 

I couldn’t resist asking if ‘Knock Out’ had made Radler a rich man.

“Yup,” he answered cheerfully.

Patented and trademarked plants like these generate royalties, and they keep this self-confessed plantaholic in the chips, able to expand his “little estate,” put up a new greenhouse and indulge his fascinations.

More roses are in the works – low-maintenance hybrid teas, fragrant roses, climbers, roses in new colors. But Radler also has an eye for other garden-worthy introductions like a hardy perennial verbena with an outstanding fragrance called ‘Sweet Thing’ and a version of the old-fashioned orange daylily with handsome striped foliage.

Still, his first rose introduction was the most thrilling. Radler can pinpoint the moment when he knew ‘Knock Out’ was truly launched as a pace-setting rose.

“I had a neighbor adjacent to my rose testing area who was generally pretty critical,” Radler says. “One day she pointed to 8920.1 and said ‘If you could produce more roses like that you’d really have something.’”

The original ‘Knock Out’ has now been joined by six other Radler varieties: 'Double (red) Knock Out,' 'Pink Knock Out,' 'Double Pink Knock Out,' 'Blushing Knock Out,' 'Rainbow Knock Out' and 'Sunny (yellow) Knock Out.' For more on Knock Out roses, including where-to-buy information, see Star Roses and Plants