Knock outs are very hardy but it is important that they go into dormancy well-watered. A dry plant is susceptible to winter die-back. Stop fertilizing and don't prune in the fall. When the ground is frozen, put 4 inches of mulch over the crown (and remove in early spring). The idea of winter mulch is not to keep the roots/crown warm. It is to minimize freeze and thaw cycles. That's it!
Answered on September 14, 2017
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