How to Trim Knockout Roses

Use a pair of sharp pruning shears to trim the Knockout rose trees in the summer to keep their shape. Cut back the outward growth one-third. Even out the side limbs. If some branches are growing faster than others, trim those back.

During the pruning season of spring, it's safe to cut the Knockout rose tree down to 12-inches tall. The Knockouts are okay if left alone--their growth will not over dominate--but if your yard size is limited, cut them back.

Remove faded and dying blooms, with a pair of garden snips, to encourage new growth. Although, the Knockout rose trees are considered self cleaning and do not require dead-heading.

Do not trim your Knockout roses in the fall to prevent damaging the plant and hindering new growth. Always trim the trees before new growth emerges but after winter frost.