Floridata Plant Encyclopedia

A Floridata Plant Profile 1063 Rosa Radrazz

Common Names: Knock Out™ rose Family: Rosaceae (rose Family)
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red Knock Out rose
This Knock Out rose bud will burst forth in just a few hours but there's no rush on my account - what a beauty!


What is all this fuss about? Only the greatest development in rose breeding ever. The Knock Out™ rose is resistant to most rose diseases, blooms repeatedly all growing season long, is heat tolerant, cold tolerant, and drought tolerant. The first Knock Out™ rose produced terminal clusters of fire engine red, tea scented flowers with seven petals. It is still one of the most popular cultivars in the Knock Out™ family, but more are being developed and introduced every year. There are pink Knock Outs™, yellow Knock Outs™, multicolored Knock Outs™ and double Knock Outs™. Perhaps the most significant breakthrough in the Knock Out™ rose is its resistance to blackspot disease, a fungal disease that has caused most gardeners east of the Mississippi to just give up growing roses. The Knock Outs™ are bush roses that get about 4 ft (1.2 m) high and 3 ft (1 m) wide. They bloom all season long and do not need to be deadheaded. The foliage turns burgundy in fall.

red Knock Out rose
This Knock Out rose is four days old and still maintains its good looks as it poses in the late evening sunshine.


Knock Out™ rose was developed by William J. Radler, a rose breeder from Wisconsin. Mr. Radler crossed a Razzle Dazzle™ rose with a Carefree Beauty™ rose, both of which are patented roses. Knock Out™ was first introduced into the horticultural trade in 2000 by the Conrad-Pyle Company, also known as Star Roses™.


Light: The Knock Out™ roses are tolerant of partial shade. They are happy with eight hours of sun per day, and positively ecstatic in full sun. Moisture: Once established, the Knock Out™ roses are drought tolerant. Hardiness: USDA Zones 4 - 9. The Knock Out™ roses require protection in winter if temperatures are to fall much below around 20° F (-7 C). Propagation: The Knock Out™ roses are patented (PP 11836), and it is illegal to propagate them vegetatively without a license from the patent holder, Conrad-Pyle Company.


These fabulous roses can be used anywhere in the landscape you want constant color from a neat, compact shrub. It is said that the Knock Out™ is probably the longest blooming rose on the market. Grow them in hedges, borders, and, spectacularly, in mass plantings. Most modern roses must be sprayed weekly during the summer months to prevent blackspot disease. Not so the Knock Outs™. Many people have been growing Knock Outs™ in containers that can be kept from freezing in winter. Knock Out roses™ are not especially well suited for cut flowers. Some members of the Knock Out™ family have a tea rose scent, and some are not fragrant.

Knockout rose
Knock Out™ roses are perfect for low maintenance plantings and are non-stop bloomers in all but the coldest weather (here in Zone 8B they bloom all year).


William Radler began his passion for roses when he was just nine years old in his parents' garden near Minneapolis, Minnesota. By the time he was 17, he was growing perfect roses and winning blue ribbons at rose shows. But growing roses is a lot of work and, soon he was hybridizing roses, trying to "...breed the maintenance out of roses," as he put it. In 1988, after more than 15 years of cross breeding, and testing for disease resistance, adaptability, floral quality and hardiness, and then more cross breeding, William Radler had a rose he believed would be the answer to every rosarian's prayers. He submitted his Knock Out™ rose to the Conrad-Pyle Company (Star Roses™) for testing in 1992. The rose was introduced to the horticultural trade in 2000 and immediately began piling up awards. Today, Mr. Radler has hundreds of roses in his trial gardens and we gardeners couldn't be luckier!

Steve Christman 10/16/07, 3/21/08, 9/4/08

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Rosa species profiled on Floridata:

Rosa Radrazz

( Knock Out™ rose )

Rosa banksiae

( Lady Banks rose, banksian rose )

Rosa laevigata

( Cherokee rose )

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