Gardeners may plant Knock Out roses for their reputation as carefree shrubs, but these varieties do require care, including some pruning. In Tennessee, the best time to trim Knock Out roses will depend on what garden task you have in mind.
After the first hard freeze in fall is the best time to trim Knock Out roses to prepare them for winter, according to the Tennessee Rose Society. The society recommends trimming out dead wood and cutting living canes back by about 1/3.
Do an early spring pruning of Knock Out roses after the last hard frost, recommends the Conard-Pyle Co. website, removing 1/3 to 1/2 of the growth, cutting back to 12 to 18 inches. In Tennessee, the best time to complete spring trimming is by mid-March.
Although Knock Out roses don't require dead-heading to keep blooming, the best time to trim off the spent blooms to spruce up your plants during the Tennessee summer is after each flush of blooms. When the petals have dropped and new buds are forming, your shrubs will look neater if you trim off the spent blooms before they form rose hips. At summer's end, you can leave some hips until winterizing, advises the Tennessee Rose Society.