Knockout roses are known to be very hardy in most regions. The knockout rose is generally a repeat bloomer, likes to bloom in the spring, is disease- and pest-resistant and drought-tolerant. The blooms are usually cherry red or hot pink. However, severe frost can seriously damage or even kill unprotected knockout roses.
Frost can cause unsightly damage or even kill knockout roses. Frost damage can cause stem discoloration, root damage, stem damage and dead blooms. In addition, knockout roses can continue to struggle well into spring and summer trying to heal itself. Decreased blooms, inadequate foliage and stunted growth can all be signs of damage caused by frost the previous winter.
Frost damage can be identified by examining the plant. Check for discolored stems that may be turning brown, golden, or black. Peeling, splitting and tearing of the bark can also be signs of frost damage on knockout roses. Sudden death of blooms, buds and leaves are also signs of frost damage if it is occurring during the winter months.
When knockout roses are left unprotected, frost damage can be caused by heavy frost, severe winds, extremely low temperatures, ice, snow and freezing rains.
Frost damage on knockout roses can be prevented in a number of ways. One of the easiest ways to protect them is to wrap them with burlap, sheets or another breathable cloth material that will protect them from the elements.
In addition to wrapping the roses, mulching can also help to prevent severe root and lower stalk damage. Mulch knockout roses using straw, wood chips other other organic material. Thoroughly cover the roots and base of the bush to prevent frost buildup.
The only way to treat frost damage on knockout roses is to remove the damage. After the danger of cold snaps and frosts have passed, cut knockout roses back to remove any unsightly damage. Do not trim, deadhead or prune the rose bush anytime during the cold weather. If cut too early, the first sign of warm weather will activate new growth. That new growth will be damaged and further injure the plant during the next cold snap.