When is the best time to cut, dig, and transplant blackberry canes, specifically thornless ones, that have set roots?
This could be done in fall or spring. It is probably best to do it while the canes are dormant. Canes whose tips reach the ground in late summer will typically root. These can be cut off, usually 4 to 6 inches above soil level to provide a handle to transport the new plant, and transplanted to about the same depth as they were previously growing. If transplanted in the fall, a 2- to 3-inch layer of mulch (e.g., bark chips, straw, leaves) should be placed around the plants to prevent the roots from heaving out of the soil during winter freeze/thaw cycles. The mulch would still be a good idea for spring transplanted canes but not so crucial as for those transplanted in the fall.