Jennifer Schultz Nelson
Extension Educator, Horticulture
Unless you've had some strange reason to purposefully avoid all garden centers and plant catalogs in the last few years, you've probably heard of Knock Out™ roses, and may even have at least one in your yard. These hugely popular shrub roses currently are available in the originally released cherry color, a double blossom in cherry, and a single flower in a blush pink. I have been asked, "Why don't 'they' make some more colors of Knock Outs™"? If only it were that simple.
Consumers stalk catalogs and garden centers each spring looking for the latest and greatest plants, always expecting something way better than what was new last year. Few people ever stop and consider what is involved in developing new plant cultivars. Granted, there is a lot of good old fashioned hard work in growing and testing plants for market. But there are also elements of science, art, and chance, where a breeder is intimately familiar with the conditions for growing and breeding the plant, but must rely on her artistic sense to find the one plant among thousands that will be the next plant gardeners "have" to have.
Development of the Knock Out™ rose is credited to William Radler, a long-time rosarian. His personal interest in roses really fueled the dream of the rose he later named Knock Out™. His passion for roses began early in life, when at the age of nine he used his allowance to buy a rose plant at the local A & P grocery store for 49 cents. Despite his family's discouraging words, telling him his plant would surely die over the winter, Radler persisted. His plant flourished, and he shopped for more rose bargains with his allowance. Since his budget was limited, he taught himself plant propagation so he could grow even more types of roses.
To learn even more about roses, Radler joined the Milwaukee North Shore Rose Society at the age of 17. At his first official rose show, he went home with the most blue ribbons. It seemed roses came naturally to him.
What became the limiting factor for Radler's prize winning roses was controlling blackspot, a fungal disease. At one point in time he was using 18 different sprays to prevent blackspot, other diseases, and insect pests on his over 200 exhibition plants. Many of his fellow rosarians cut back on their rose gardens when faced with having to spray so intensely for disease and pests.
Radler began to wonder whether roses could be bred that would be beautiful as well as resistant to pests and disease, eliminating the need for such intense spray schedules. Essentially, his dream was to breed the maintenance out of roses. Not only would this be a great development for current rose lovers, but surely this would interest those that were new to growing roses.
Winter hardiness was another of Radler's concerns. He hated having to remember to put winter protection on his roses each year and hope that they all survived the cold. Until then, most rose breeding happened in warmer climates, contributing to the rose's reputation of being a tender plant in cold climates. Since he lived in Wisconsin, USDA Zone 5, where winters may be minus 20 degrees Fahrenheit or lower, Radler's rose breeding easily addressed this issue, as plants intolerant of the cold winters were naturally culled from his breeding populations.
Radler also developed methods to screen his breeding populations for disease resistance, drying diseased leaves and grinding them in his kitchen blender. He sprinkled his roses with this powder while the leaves were damp and watered overhead to create an ideal disease environment. He carefully observed plants, and removed those showing disease symptoms.
He also used his artistic sense to choose parents that had pleasing flower colors and form. This process continued for 15 years before the plant that became Knock Out™ was bred. The parents of Knock Out™ were bred from two distinct rose groups including at least eight known cultivars. Repeated cross-pollinations of plants showing good flower form and disease resistance continued for generations in search of the elusive plant that had all the good characteristics and none of the less desirable ones.
Rose seeds develop in the rose hip, the round structure that develops after the rose is pollinated. Most rose plants develop multiple hips that have 30 to 50 seeds inside. Some plants have partial sterility, making it difficult for them to produce seeds. The plant that produced the mother plant of Knock Out™ was such a plant. The mother plant of Knock Out™ was produced from one hip containing a single seed. The seedling it produced, the first Knock Out™ rose, was a late season runt that was nearly discarded in 1988. Allowing it to grow for another season revealed it was the plant Radler had been searching for.
In 1992 Knock Out™ was sent to The Conard-Pyle Company/Star® Roses for more thorough field testing, and by 2000, Knock Out™ was awarded the prestigious All American Rose Selection Award.
Considering how long it took for Knock Out™ to emerge from a very broad set of genetics in the parental lines, it may be awhile before we see a wide variety of color in this type of rose. If there are genes for colors in the parental lines other than variations on the pinks we've already seen, there is a chance that breeding efforts will unveil them fairly simply. Complicating matters is the chance that a seedling of a desirable new color may not have the disease and pest resistance Knock Out™ is known for. Without a doubt Radler and other plant breeders are working on this as you read this. Let's just hope that lady luck is on their side in their efforts to produce more roses like Knock Out™ in coming years.