Chrysanthemums (Dendranthema), commonly called mums, are cultivated as perennials across U.S. Department of Agriculture plant hardiness zones 5 through 10, although they are sometimes treated as annuals even within that range. These plants are prized for the colorful, plentiful blooms they produce in the fall. Regular pruning, including an annual trimming to clear spent flowers and old stem tissue off of the plants, is necessary to maintain an attractive, prolifically blooming specimen. You may opt to wait and cut mums back in late winter or early spring when new green growth emerges or cut the plants back in late fall or early winter shortly after they finish blooming.
Pinch or cut off any flower buds that begin to develop or open in late summer or early fall before you want flowering to begin to encourage a stronger, more uniform blooming period later.
Inspect the blooming mum regularly, looking for symptoms of fungal diseases like leaf spots and gray mold, which appears as fuzzy gray growth on flowers and other plant parts. Cut off any infected portions of the mum as soon as you notice the problem and when conditions are dry. Make the cut just above a leaf node or stem junction well below where any symptoms appeared. Bag and destroy or dispose of the removed plant parts to avoid spreading disease.
Wipe or spray the cutting blades of the pruning shears with rubbing alcohol or a 10 percent bleach solution between uses or after each cut if you are removing diseased plant portions.
Cut the spent flowers and mum stems off about 6 inches above the ground after the plant has finished blooming.
Dispose of the removed mum stems and flowers away from the mums and other desirable vegetation to prevent the accidental overwintering or spread of diseases.
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Things You Will Need
- Sharp, clean pruning shears or other trimmer
- Rubbing alcohol or bleach solution
- Every few years, mums benefit from a rejuvenating division in late winter or early spring as new growth is emerging.
- Lightly prune mums repeatedly throughout the growing season to encourage a dense, bushy appearance by the time the plant flowers in the fall.
- University of California Statewide Integrated Pest Management Program: Chrysanthemum
- University of California Cooperative Extension: October Flower of the Month -- Chrysanthemums
- Kansas State University: Perennials
- Some Like It Hot: Flowers That Thrive in Hot Humid Weather; P. J. Gartin
- Better Homes & Gardens Perennial Gardening; Better Homes & Gardens
- Digital Vision./Photodisc/Getty Images