Rhubarb is typically propagated by division. In early spring or late fall, choose a mature plant that is at least four years old and has a good root system. Cut away the leaves and stems, leaving only a small section of the crown and roots. Using a sharp spade or knife, carefully divide the crown into sections, making sure each one has at least one strong root and several buds. Replant the sections in well-draining soil, spacing them 3-4 feet apart, and water thoroughly. The new plants should be watered regularly for the first few weeks until they become established.