Planting
For use as a perennial, plant in early spring or at least 6 weeks before a killing frost in fall. Planting chrysanthemums in spring will give them the best chance of surviving the following winter. If you are using them as an annual pop of fall color, plant them when blooming in late summer or early fall.
Watering
Mums require frequent watering due to their shallow root system, especially in high heat. A layer of mulch in summer will help conserve water and keep the soil moist and cool.
Pruning
Pinch approximately 1 inch from the branch tips two to three times during the growing season to encourage branching and a sturdier plant. Early bloomers that bloom in mid-September, should be pinched no later than mid-June. October bloomers can be pinched up until mid-July, with the rule of thumb being not to pinch any closer than 3 months to bloom time.
Propagating
When grown as perennials, they can be divided every two to three years in the spring. Dig up the plant when new growth begins to appear, discard the dying center and re-plant the new shoots on the outside of the plant. They can also be grown from cuttings taken in the spring. Cut just below a leaf node and root in sterile potting soil. The new plants should be watered daily and kept in a sunny windowsill until established.
Fertilizing
Mums are not big feeders, so it is best to apply a dilute fertilizer several times before bud set. A 5-10-5 fertilizer formulation will have the greatest effect on flower production and overall growth.
Treating
Some diseases that can affect them are leaf spot, powdery mildew, and viral diseases such as mosaic or stunt. Avoid overcrowding and overly shady locations that cause moisture to remain on the leaves and provide a habitat for diseases. Pests can include aphids, caterpillars, leafhoppers, leafminers, plant bugs, and spider mites.