Chrysanthemums should be divided every three to five years to avoid overcrowding and promote maximum flowering. They should be divided in the spring when new growth appears. Dig entire clumps and separate the plants with a sharp, clean knife or spade. Remove all dead and diseased plant parts.
Replant the divisions as soon as possible in a loose, well drained, rich organic soil. Chrysanthemums should periodically be moved to a new location, but if this is not feasible, the soil should be sterilized chemically to reduce danger of disease and insect problems.
Young divisions will grow much faster and provide a better plant than crowded old clumps. When the new shoots are 1-3 inches tall in early spring, dig up your old clumps and carefully pull them apart. plant the healthy divisions into newly prepared fertile soil and discard the half dead woody parts.