How to Prune Knockout Roses
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Allow your knockout roses to grow the first year without pruning. This will give your shrub time to take on a shape.
Prune after the first year at the end of winter while the plant lies dormant.
Remove the dead wood with garden snips. Remove excess canes from the bottom of the shrub.
Trim the knockout rose to one-third of it's size with garden snips. Cut the limbs just above an outward-facing bud sloping toward the shrub at a 45-degree angle.
Deadheading isn't needed to encourage new blooms. but it does help to make your plant more attractive between flowerings.