Chester Blackberry

Chester Thornless was developed cooperatively by the USDA Agricultural Research Service and Southern Illinois University, from a cross of the breeding lines SIUS 47 and Thornfree made in 1964, with selection and evaluation continuing for nearly two decades before its commercial release in 1985. Its central breeding objective was cold hardiness: earlier semi-erect thornless blackberries generally could not reliably survive past USDA Zone 6, and Chester was specifically bred to hold cane viability into Zone 5, a real practical improvement that made thornless blackberry growing viable much further north. It remained, for decades, the hardiest widely available thornless blackberry selection, and it is still commonly planted alongside Triple Crown as a complementary pairing, since its full ripening runs from mid-August into September, extending the harvest window.