Knock Out provides a new punch to the garden. It’s a super-vigorous, disease-resistant, repeat-flowering, cold-hardy rose that grows into a head-high shrub inside of two years. Since its introduction in 1988 it has taken the eastern half of the United States by storm, leading millions of gardeners who had ignored or abandoned them to grow roses. In its first year alone it sold 250,000 units, and it has been about as popular ever since. But for all their popularity, Knock Out and its close kin have been ridiculed by the most serious of the rose faithful. Why? Partly because they are not hybrid tea roses, and as such they don’t conform to our expectations for what a rose ought to be. Partly because they have become common, or faddish. Partly because they are not fragrant.