Add a pop of vibrant red to your landscape with the Knockout Rose 2 gal. Double Knockout Rose Bush. The Red Double Knockout rose bush has quickly become a favorite shrub for gardeners all over the U.S. and beyond. From the same breed that created the original Knockout Rose, the Double Knockout rose bush packs twice the punch with twice the petals. Traditionally, each medium-sized bloom will range from 18-24 petals. From spring to fall, the Red Double Knockout rose bush produces velvety red double blooms that are deeply reminiscent of classic roses.