Knockout roses are a fairly easy variety to care for, but the bush is not exempt from the necessity to trim. In order to keep a healthy knockout rose bush, you will have to trim back all the dead blooms.To prune use thick gardening gloves and bypass pruners that have been sharpened for a clean cut. As you trim back all the dead blooms, make the cut is about a quarter of an inch above a leaf bud. When you prune, make sure the slant of the cut is at an outward angle. While pruning, dip your pruners in solutions such as rubbing alcohol to disinfect them. It will prevent any possible existing rose disease from spreading to the rest of the bush. If pruning in the fall, prune before the first frost and always prune any dead, damaged or diseased wood.