Can I prune my knockout roses during the summer. If so, how much?
You can prune your Knock Out© roses during the summer months but major pruning should be done in late winter or early spring. In summer you can cut back any long shoots by any amount needed to preserve the shape of the shrub. Use a by-pass pruner and cut the stem about 1/4 inch above an outward-facing side shoot or bud. As always, remove any dead, damaged or diseased branches. Also remove any suckers that have grown from below the graft line. Wear gloves when you prune.
More extensive pruning should be done in late winter or early spring just as the buds are beginning to break. Cut back the branches to about 1/3 or 1/2 of their length or 1 or 2 feet shorter than the final height that you want to achieve.
Curtesy of NYBG Plant Information