EHOW tells us….
Step 1Water the mums regularly. Soak the mums until water runs out through the holes in the pot bottom. After the initial soaking, water daily or until soil is moist. Don’t allow the potted soil to dry out, as this will harm the plant.
Step 2Keep mums in natural light or in the direct sun, whether indoors or out. Mum plants need plenty of sun for proper growth. Keep them away from night lighting, as this disturbs their flowering cycle.
Step 3Deadhead spent blooms. After flowers begin to wilt and die, pluck them from the plant at the base of the flower. Leave on any buds, blooming flowers and leaves.
Step 4Allow the mum plants to go dormant over the winter. Keep them outside once the blooms die, and mound the pots with dried leaves or garden refuse to prevent premature freezing.
Step 5Prune the mum plants in the late winter or early spring before new growth begins. Cut back stems to about 12 to 18 inches or shorter for bushier plants.
Step 6Water mum plants in the spring as new growth begins and color returns to the plants. Keep them well watered throughout the spring, fertilizing once a week for the first couple months and then ceasing fertilization once blooms are present.