Cultivated blackberries (Rubus fruticosis) grow on thorny or thornless canes in erect, semi-erect or trailing forms. Thorny blackberries, typically erect cultivars, will survive freezing temperatures. You can grow them in U.S. Department of Agriculture plant hardiness zones 5 through 10. Thornless blackberry cultivars are less cold-hardy.
Thorny Blackberry Low Temperatures
Thorny blackberry cultivars grow on stiff, arching canes and bear larger blackberries than semi-erect cultivars and those that trail along the ground. All three forms benefit from being grown on a trellis. While thorny blackberries will survive freezing winter temperatures, there is a limit to how much cold they can withstand. Zone 5, the coldest limit of their growing range, has average winter low temperatures of minus 20 to minus 15 degrees Fahrenheit. Winter temperatures drop to only 10 F in North Carolina, however.
Some blackberry canes die each year, but not because of winter low temperatures. Canes that grow in the first growing season are primocanes; they usually do not produce fruit. After their first winter, they are called floricanes. Floricanes bear fruit in late summer or early autumn then die.
Winter Chill Requirement
Depending on where you live, you may need to choose a thorny cultivar that will grow in mild winters. Blackberries have winter chilling requirements, hours of temperatures below 45 F that are necessary for them to blossom and bear fruit. Thorny blackberries typically need more chilling hours than thornless cultivars, but there are some low-chill, thorny types available. “Kiowa” needs just 200 hours of winter chilling temperatures and bears large high-quality blackberries. “Prime-Jan” and “Prime-Jim” both need 100 to 300 hours. In contrast, “Chickasaw” requires 500 to 700 chill hours.
Thornless Blackberry Hardiness
In comparison to thorny cultivars that can survive USDA zone 5 winter lows of minus 20 F, thornless cultivars have a limit of minus 10 F, report University of Kentucky researchers. Oregon State University horticulturists found that cold may damage the canes and buds of thornless trailing blackberry cultivars when the temperatures drop below 13 F in December or early January. In late winter they might be damaged at 20 F.
- Oregon State University: Blackberry Cultivars for Oregon
- North Carolina State University Cooperative Extension: Blackberries
- Texas A&M University: Blackberries
- Oklahoma State Cooperative Extension Service: Commercial Blackberry Production
- University of Kentucky: Site Selection for Thornless Blackberries Based on on Past Kentucky Low Temperature Weather Data
- Colorado State University: Growing Blackberries in the Home Garden
- Old Farmer’s Almanac: Blackberries
- USDA Agriculture Research Service: USDA Plant Hardiness Zone Map
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