Should You Cut Back Knockout Roses in Zone 5 in the Spring or Late Fall?

Pruning Benefits

• Roses bloom on new wood, so you need to prune them from time to time to make room for new growth and to encourage flower production. Throughout summer, repeat-bloomers, such as "Knock Out," perform best if they are deadheaded to remove spent flowers and encourage the next cycle of blooming. In USDA zone 5, you can expect two to four blooming cycles per season. Late fall pruning is not recommended for roses in any planting zone.

Spring Pruning

• In USDA zone 5, rose bushes should be pruned back with handheld pruners in early spring, when the leaf buds begin to swell. Remove canes that are dead, diseased and old, leaving five to seven evenly-spaced, outward-facing canes that are young and healthy. Cut the remaining canes to 12 inches. Cutting just above an outward-facing node -- leaf bud -- ensures outward growth that forms a pleasing, vase-shaped plant.

Deadheading

• After the first flush of blooms fades in early summer, trim "Knock Out" back with pruners or hedge clippers. Cut just enough to remove spent flower heads -- about 3 to 6 inches. Repeat deadheading in the same manner after each bloom cycle. Make your last trimming no later than August. Fresh growth that results from late pruning won't be sufficiently hardened off to withstand the early frosts that typically occur in USDA zone 5.

Tips

• Fertilize "Knock Out" roses each time you prune with a balanced, general-purpose fertilizer, such as 10-10-10, for the best blooming. Sprinkle 1/4-cup fertilizer over the root zone of each rose. In fall, it is okay to trim away stray canes that might cause a nuisance, such as those that overhang walkways or whip in the wind. Prune out dead and diseased plant parts any time of year. The pruning techniques you use for "Knock Out" roses will come in handy when you prune many other shrub rose varieties.