Rose fanciers, who tend to fuss over every aspect of rose care, will be disappointed by the Knockout rose; winter care for these easy-to-grow shrub roses is as uncomplicated as for any other garden perennial. “Knock Out” roses were bred by William Radler, a pragmatic Wisconsinite landscape architect who set out to breed a carefree rose that he wouldn’t have to fuss over after he retired as director of the Boerner Botanical Gardens in Milwaukee. In his “Knock Out” roses, first introduced in 2000, he accomplished his objective.
Remove summer mulch. Clean out any dead or broken branches when the shrub stops blooming and drops its leaves.
Allow plants to go dormant naturally. Stop fertilizing in late August. Continue watering Knock Outs just like any other perennials, until the first hard freeze.
Mulch plants loosely with leaves, or a mixture of clean compost and leaves, in a chicken-wire cage, or wrap in burlap with twine, to protect them from drying out where winter winds are strong or wind chills are frequently below zero. Insulate plants by mounding clean compost and leaves about 4 inches over the crown of the rose bush. Plants should not need winter protection south of USDA zone 4.
Clean off any winter mulch in late winter before the ground begins to warm. Cut back any branches that cross others and branches that have broken or died back during the winter.
Prune after the last hard frost; choose four or five healthy-looking main branches that will form the basic shape of the shrub, and prune them back to between 8 and 12 inches long. Remove other branches.