This method of vegetative propagation, called layering, promotes a high success rate because it prevents the water stress and carbohydrate shortage that sometimes plague cuttings. Layering is enhanced by girdling the stem where it is bent, by wounding one side of the stem or by bending it very sharply. The rooting medium should always provide aeration and a constant supply of moisture. Insert the shoot tip and cover it with soil. The tip grows downward first, then bends sharply and grows upward.
Roots form at the bend and the recurved tip becomes a new plant.
Remove the tip layer and plant it in early spring or late fall. This method is successful with purple and black raspberries and trailing blackberries. Figure 1.21a Simple layering. Cover part of it with soil, leaving the last 6 to 12 inches exposed. Bend the tip into a vertical position and stake in place.