Chrysanthemums, or mums, are often purchased in full bloom to decorate porches and gardens during the autumn season. Once the flowers fade and cold weather arrives, gardeners must determine the proper end-of-season care. This process is not one-size-fits-all, as the subsequent steps depend entirely on the type of plant purchased. Understanding how to manage these plants after their fall show is the foundation for either encouraging their return next year or disposing of them properly.
Determining the Type of Mum
Not all chrysanthemums available in the fall are intended to survive the winter, making identification the first step in post-season care. The two main categories are “hardy garden mums” and “florist or decorative mums.” Hardy garden mums are bred as perennials, possessing the capacity to withstand colder temperatures, typically in USDA Zones 4 through 9. Florist mums, often sold tightly packed with blooms, are generally treated as annuals due to their shallow root systems and breeding focused on dense flowering rather than winter survival.
Garden mums usually have more visible foliage and fewer, larger blooms. Florist varieties are so densely covered in flowers that the leaves are barely visible. Checking the original plant tag for a hardiness zone or the words “perennial” or “garden mum” offers the best clue. If the tag is missing, assume a heavily budded, grocery-store-purchased mum is a decorative annual not intended for overwintering outdoors.
Essential Steps for Overwintering Perennials
For mums identified as hardy perennials, preparing them for dormancy requires specific physical steps once the blooming season ends. After the foliage has died back naturally or following the first hard frost, the stems should be cut back. This pruning helps manage debris and prevents the plant from expending energy on dead growth.
The spent stems should be trimmed down to a height of approximately four to six inches above the soil line. Leaving this stubble helps the gardener locate the plant’s crown for later mulching and provides a point of reference for new spring growth. If the mum was purchased in a small pot, planting it directly into a well-draining garden bed is beneficial, as the insulating capacity of the surrounding earth is much greater than a container. Planting in the ground is necessary to allow the plant’s root system to develop the underground shoots, called stolons, which are needed for winter survival and return the following year.
Providing Cold Protection and Winterizing
Once hardy mums are established in the ground, they require additional preparation to protect them from the harsh conditions of winter. The primary threat to overwintering mums is not the cold itself, but the repeated freeze-thaw cycles that can push the plant’s shallow root system out of the soil, a phenomenon known as frost heaving. Applying a thick layer of insulating material minimizes temperature fluctuations in the soil.
A layer of loose, airy mulch, about four to six inches deep, should be applied after the ground has frozen solid. Materials like straw, pine needles, shredded leaves, or evergreen boughs are recommended because they are light and do not compact easily, which helps prevent moisture buildup. Avoid applying mulch before the ground freezes, as this can trap warmth and encourage premature new growth that will be damaged by later cold. Proper drainage is also important, since wet, soggy soil is a significant cause of root rot during the dormant winter period.
The protective mulch should be left in place throughout the winter to shield the root crown from cold and heaving. Gardeners should check the soil periodically during dry winter spells, ensuring the roots remain lightly moist, similar to a wrung-out sponge, but never saturated. This mulch can then be carefully pulled back from the plant’s crown in early spring when the danger of severe cold has passed and new growth begins to appear.
Handling Spent or Annual Varieties
Mums determined to be florist annuals, or any perennial the gardener chooses not to save, should be properly disposed of once flowering is complete. If the plants show any signs of disease, such as powdery mildew, or are infested with pests, they should be discarded in the trash rather than composted. This practice limits the spread of pathogens and insect eggs to other areas of the garden.
Healthy foliage and stems, however, can be safely added to a home compost pile to return organic matter to the soil. Alternatively, the spent, healthy stalks can be left standing in the garden temporarily over winter. These dried stems can provide visual interest in the landscape and offer shelter for beneficial insects. They can be removed and composted in early spring before garden cleanup begins.