The vibrant colors of chrysanthemums, commonly called mums, signal the peak of the autumn season. Once blooms fade and the first hard frost arrives, the foliage browns and dies back, marking the start of the dormant phase. Proper post-bloom care is important for maintaining garden health, preventing disease, and ensuring the return of perennial varieties next year. This care directly impacts the plant’s ability to survive the cold and thrive in the subsequent growing season.
Determining the Type of Chrysanthemum
The most important step is to correctly identify the type of mum you have, as this determines the next course of action. Chrysanthemums are generally categorized into two groups: hardy garden mums and florist or pot mums.
Garden mums are typically perennial varieties, bred to develop a robust root system that includes underground shoots called stolons, allowing them to overwinter successfully in many hardiness zones. They often display more visible foliage beneath their flowers and are usually purchased from nurseries in the spring or early fall.
Florist mums are cultivated primarily for their immediate, dense floral display in the fall and are treated as annuals. These plants are often heavily pruned and forced to flower in a compact pot, preventing them from establishing the deep, hardy root system necessary for winter survival. They are identifiable by their extremely dense bloom coverage, where the foliage is barely visible, and their shallow root ball. Florist mums should be fully removed from the garden, while hardy mums require cleanup and protection.
Immediate Cleanup and Pruning
Once the foliage has fully browned or collapsed after a killing frost, begin the cleanup process. For hardy, perennial mums you intend to keep, cut the dead stems back to approximately 4 to 6 inches above the soil line. This remaining stem material helps catch insulating snow and marks the plant’s location during dormancy. Use clean, sharp pruning shears to make the cuts, preventing ragged edges that could invite moisture and decay.
Sterilize cutting tools beforehand with a 70% isopropyl alcohol solution to avoid transferring fungal spores or pathogens from other plants. For annual florist mums, or perennial mums that failed to establish robust roots, the entire plant should be cut down to the soil level and removed completely. Removing the spent foliage and stems helps eliminate overwintering sites for pests and fungal diseases like powdery mildew or leaf spot.
Winter Protection and Disposal
The final steps involve disposing of cut plant material and protecting the remaining perennial roots. If the foliage showed signs of disease, such as yellowing, rust-colored spots, or white powdery residue, it should be bagged and disposed of with household trash. Diseased material should never be added to a home compost pile, as the internal temperature may not reach the 140–160°F necessary to kill persistent pathogens.
Healthy, perennial mums require protection from frost heave. This occurs when repeated freezing and thawing cycles push shallow root systems out of the ground, exposing them to cold air and drying winds. To prevent this, wait until the ground has fully frozen, then apply a loose, airy mulch, such as 3 to 4 inches of straw or pine needles, over the crown of the plant. This insulating layer helps maintain a consistent, cold temperature in the soil, preventing the damaging fluctuations that cause heaving.