To maintain a size of 3–4’ w x 3–4’ h, Knock Out Roses should be cut back once a year to 12” high.
Check your rose bush from time to time in late winter/early spring, and when you start to see new shoots growing from the canes on your rose bush, that’s a good sign that it’s time to prune. Oct 07, Knockout roses are a relatively low-fuss variety that can make a welcome addition to any yard or garden, but they do require a little seasonal pruning in order to grow healthy and beautiful.
Cut back your roses extensively at the beginning of spring, and shape them up as needed throughout the rest 96%. May 18, A: Knock Out rose is a plant I can recommend to any gardener.
It blooms so heavily, it is so pest resistant, and it is so tough, hardly anyone has a bad experience with it. Mine has deep red blooms each summer. Double Knock Out, Blushing Knock Out and Pink Knock Out ‘are also on the market.
Knock Out blooms continuously from April. The degree to which you are pruning would be considered rather severe for Knock Out roses. The heights you are using apply more to hybrid tea and grandiflora roses. Research indicates that Knock Out roses respond best if not cut back lower that 24 inches for the hard pruning in early spring, and more moderately in the fall.