Temperature Hardiness of Knock Out Roses

Cold Tolerance

• Knock Out roses are winter hardy to U.S. Department of Agriculture plant hardiness zone 5. Zone 5 includes parts of the Midwest such as Illinois and Kansas, plus some parts of Utah, Nevada and California. Generally, the coldest weather in the plant’s northernmost hardiness range averages minus 10 to minus 20 degrees Fahrenheit. In the extreme southern end of Knock Out's range, winter temperatures rarely drop below freezing.

Cold Protection

• In colder parts of its growing area, protect the Knock Out roses with a thick layer of mulch, spreading it around the base of the plant and making sure it is well drained. Wrap the rose bush with burlap, if needed, to keep it from drying out when cold winds blow.

Heat Tolerance

• Knock Out roses hold up to heat and humidity through USDA plant hardiness zone 9, according to University of Florida IFAS Extension. In terms of American Horticultural Society heat zones, zone 9 -- which averages 150 days above 86 F -- is the warmest extreme for Knock Outs. According to Conard-Pyle, which markets the Knock Out series, the roses are heat tolerant throughout the U.S. The plant requires at least six hours of full sun per day to produce the highest-quality flowers.

Heat Protection

• Mulching around roses is standard practice, but be sure to spread a thick layer of mulch around roses during extended periods of hot weather. This will help keep the roots cool and retain moisture. Give the Knock Out roses extra water during unusually hot, dry spells. If the Knock Out rose is growing in full sun, consider shading the plant during blistering summer afternoons.