“It’s a great feeling to know that I contributed in developing low-maintenance roses,” Radler says.After discovering a passion for roses in my youth, I eventually tried my hand at breeding new roses. I began with cold tolerance and was successful. Later I discovered my ultimate passion was to breed roses that were hardy, resistant to diseases and pests and would need little preventive sprays to stay healthy. This was a bit more difficult to achieve.
Black spot, in particular, is a rose nemesis and occurs in humid climates east of the Mississippi. To combat black spot, chemical sprays are applied weekly for months. I wanted to build a rose with an extremely high resistance to black spot so that these sprays wouldn’t have to be used. This led me to wonder if the genetic raw material in wild roses could be shifted into the “modern rose” through selective breeding. I realized that breeding for disease resistance against black spot, fungus and insects would save gardeners from 15 or more sprays per year and would ultimately become more environmentally friendly.
The Beginning
Hybridizing a new rose requires shuffling rose genes through cross-pollination. Seldom are the most desirable traits found in just one rose. Many varieties and tries produce many more inferior roses than just one good rose.
Another obstacle is the lack of fertility in cross-pollinated roses. Often, when the results are close to what is desired, it isn’t possible to breed any further into the next-generation because plants are often sterile females that can’t produce seed. For those roses that do produce seed, it takes three months or more for the seed to ripen in the hips. If these difficulties aren’t enough, sometimes only one in five seeds will germinate. The low frequency of successful cross-fertilization attempts – one out of three – often leads to repetitive failures.
Every year in my half-acre plot, I observed the old and new roses – hoping to spot a breakthrough. Although each year seemed to produce advancements, most of my hybridized “offspring” were flawed. Dominant genes frequently overpowered, producing inferior traits such as poorly formed flowers with tissue-thin petals, odd colors that faded unattractively, gangling stems armored with vicious thorns, inconsistent repeat blooms and a high susceptibility to disease and pests of all kinds. Still, with the odds against me, I persevered.
Knock Out is the result of years of breeding efforts to attain a virtually maintenance-free rose.Step by Step
Tolerance to cold seemed the easiest goal to achieve. During my observations and trials, I coined the term “crown hardy,” meaning that during cold winter temperatures, stems may be killed to soil level while remaining uninjured below. Rose plants having this trait perform well season after season without winter protection.
The crown-hardy roses benefited from mulch applied to the soil year-round and aided in acclimatization the first winter. To produce hardiness and disease resistance, especially to black spot, I used the roses Applejack, Carefree Beauty and Eddie’s Crimson. Through trial and error, I developed a process where I collected diseased leaves early in the season, dried them on sheets of newspaper and blended them into a powder. I sprinkled the powdery substance copiously over the entire rose garden while the rose leaves were wet. To make sure that each disease had a good chance to infect the roses in the test, overhead watering added extra moisture, encouraging disease.
Black spot usually presented within two weeks of this inoculation. Before the growing season ended, the highly disease-resistant plants were easy to spot among the devastation in my garden. A friend of mine called this practice “benign neglect.”
Pollination Perseverance
Striving to breed the maintenance out of roses, I found myself working harder than ever, performing all the usual gardening tasks along with keeping copious records.
In an average year, I made about 500 to 1,000 cross-pollinations, grew 300 to 500 roses from seed under fluorescent lights in my basement, which I planted in my backyard “laboratory.” In the process of producing many dead ends, I culled about 500 roses a year from a standing inventory of approximately 1,400 roses.
After 15 years of trial and error in rose breeding, a friend pointed me toward one particular new rose and said, “You know, Bill, if all your roses were as good as that one, you would really have something.”
The rose she pointed to, after 10 years of rigorous testing throughout the nation, came to be named The Knock Out Rose (‘Radrazz’), winner of the world’s most prestigious rose award: the All-America Rose Selections award for 2000. In 2002, members of the American Rose Society bestowed their highest place for it among hundreds of recent rose introductions.
Now there are seven Knock Out Roses in the family. The original Knock Out, Double Knock Out, Pink Knock Out, Pink Double Knock Out, Blushing Knock Out, Rainbow Knock Out (an AARS winner in 2007) and Sunny Knock Out (new this year). People are always asking me, “What’s next?” Everyone wants a Knock Out climber.
Has it been worth all the frustration and long hours? You bet. It’s a great feeling to know that I contributed in developing low-maintenance roses. I’m not finished with breeding low-maintenance roses. I want easier roses in all different colors, sizes and fragrances.
The author is a plant breeder best known as the hybridizer of the Knock Out series of roses.
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