Small Fruit Blackberries (Rubus spp.) Blackberry seed, due to the dormancy of its embryo, requires stratification at 33 degrees F to 35 degrees F before being planted. The stratification requirement varies considerably with sometimes as long as five to six months being necessary. The average is approximately three months. September is suggested as the best time for planting. Treat dry seed with acid for about 30 minutes. Commercial varieties of blackberries are commonly propagated by root cuttings or tip layering.

Propagation:
Leafy Stem Cuttings. This is the most feasible method to propagate large quantities of plants. Leafy stem cuttings may be propagated from the apical 4 to 6 inches of cane when the cane is succulent but still firm. Cuttings should be placed to a depth of 2 inches in a perlite peat or peat sand mixture. The cuttings should be misted especially in the 2 to 4 week period before the roots are formed. It is important to promote good water drainage. Application of Rootone to the cut stem can also improve rooting efficiency.

Root Cuttings. All blackberries can be propagated by root cuttings. This is the fastest method to produce new plants. Cut roots 1/4 to inch in diameter into six inch strips. They can be directly planted in the new location, grown as a potted plant or they can be placed in a plastic bag in a refrigerator. When planted directly in the field uneven stands often results during the first year. Potted plants can be grown in the nursery for up to one year. When planted in soil they should be covered with 2 to 4 inches of soil. Planting is best accomplished during the winter. Substantial quantities of suitable roots can be had by plowing a furrow and severing the roots adjacent to the mother plant.

Suckering. The easiest and most rapid method to propagate blackberry is to utilize the suckers that naturally form from roots. Simply sever the sucker from the point of attachment with the mother plant and move it to its desired location. Removing suckers has minimal or no impact on the mother plant. Genetically thorny blackberry cultivars will remain thorny and genetically thornless blackberry cultivars will remain thornless whether propagated from stem cuttings, root cuttings or suckers.

Tip Layering. Semi-erect or trailing blackberries can be propagated by tip layering. Tip layering sometimes occurs in nature and it is a viable method for the homeowner to propagate a relatively few plants. The technique is to bring first year vegetative shoots into contact with the ground and cover the shoot under approximately 3 inches of soil. A more efficient method to tip layering is to remove the shoot apex to induce lateral branching. Next, during the summer dig a 3 inch deep hole which is sloping toward the mother plant and vertically away from the plant. Place the terminal end of the shoot in the hole with back vertical portion of the hole. Then cover the shoot with 3 inches of soil. By the fall new rooted shoots will have developed and newly layered shoots should be transplanted in the spring.

If it were me, I would try stem cutting with Rootone.