Take 4- to 6-inch-long softwood tip cuttings, about the diameter of a pencil, from barberry plants in summer. Select healthy, vigorously growing branches from the barberry's upper parts. Make a smooth, slanting cut below a node.
Remove all leaves from the bottom half of each cut stem. Wherever a leaf was attached is a node that will later generate roots for new plants. Place cuttings in the water jar to keep them fully hydrated.
Mix perlite and coarse peat moss 50-50 for your sterile rooting mix. Moisten it thoroughly. Fill rooting pots with rooting mix and allow pots to drain. Make three to six planting holes in each rooting pot, depending on the pot size.
Dust the bottom half of each stem with rooting compound, which will help cuttings root faster and form a stronger root system. Insert cuttings halfway into the rooting medium, making sure each has two to three nodes beneath the soil surface. Press soil firmly around each stem.
Water pots well, until excess water flows out the drainage holes. Allow pots to fully drain. Place one or two bamboo stakes into each pot, so the stakes stand several inches taller than the tallest cutting. Slip each pot inside a clear plastic bag to keep humidity around cuttings high until they root.
Place each rooting bag in a warm room in bright but indirect sunlight, such as near a sunny window. Maintain even soil moisture until cuttings root, usually in three to six weeks. Don't allow the rooting mix to dry out but also do not overwater, which encourages disease.