Blackberries propagate well from stem cuttings under special conditions. Growers with access to greenhouses and misting systems have the best success. Other methods employ the unique growing characteristics of the blackberry to create clones of the original cultivar. One easy method, tip layering, occurs naturally in untended plants.
Prune unwanted first-year canes back to the ground in midsummer. Save leafy pencil-diameter sections of canes in plastic bags. Store the cuttings out of direct sunlight until transplanted.
Fill pots with equal parts perlite and peat, and water well. Set up a workspace for the pots that won't be damaged by water and that provides indirect light for the plants. Plant cuttings 5 inches long by inserting the cut end 2 inches into the mix. Mist the cuttings with plain water.
Make a tent framework by bending a section of wire fencing into a U shape wide enough and long enough to cover the cuttings. Cut a sheet of clear Mylar and drape it over the frame; hold down the edges with scrap wood. Cut half-inch-diameter ventilation holes every foot along one side of the tent. Lift the tent daily and spray water mist over the cuttings. Cuttings should begin rooting after about two weeks, and after five weeks can be weaned from the frequent misting.
Save one or two first-year canes of established plants for tip layering. Simply bend the cane over to the ground in midsummer, without breaking it, and cover the tip with a shovelful of dirt. Bury the cane about 3 inches deep. By fall the cane tip will root and develop a new plant.
Create several plants from one tip-layered cane by snipping the tip of the cane and forcing several branches to form. Dig a hole 3 inches deep within reach of the cane, and carefully bend the blackberry cane down into the hole. Cover the junction of the branches with 3 inches of soil. Each branch will develop roots.
Sever the cane in late winter when the plants are dormant. With the branching method, snip the rooted branches from the main stem and plant to a 3-inch depth in a permanent row. Alternatively, cut the tip of the cane and transplant the single tip-layered blackberry to a permanent bed.
Blackberry Root Cuttings
Dig blackberry roots--growing a few inches underground in spreading lateral systems--during late winter when the plants are dormant. Divide the roots into 6-inch sections at least pencil-diameter.
Place the roots in plastic bags for storage until transplanted. Keep the roots in a cool, dark place. More root cuttings survive if planted in greenhouse pots for a year before transplanting to the field.
Transplant root cuttings directly to a permanent row by setting the root sections in a trench dug 4 inches deep. Compensate for a lower survival rate with a tighter spacing. Cull crowded or weak plants later in the season.