Chrysanthemums, commonly known as mums, are a staple of the autumn landscape, providing a burst of color when most other flowers have faded. When their display ends, the question of what to do next arises, especially since the term “dead” is often misleading in this context. While the colorful bloom and above-ground foliage may be spent or killed by a light frost, the root system of a hardy garden mum often remains dormant and alive beneath the soil. The decision facing the gardener is twofold: either prepare the plant’s root structure for survival through the winter to encourage a return next year, or clear the spent material and dispose of it. The path chosen determines the subsequent steps, which involve a combination of strategic pruning, sanitation, and protective measures.
Immediate Post-Flowering Pruning
The initial step after the flowering period concludes is to address the spent, unsightly plant material above the soil line. This process, known as deadheading, involves removing the withered flowers to tidy the plant’s appearance. Removing these spent blooms prevents the plant from expending its remaining energy on producing seeds. A more substantial cutback of the entire plant is also necessary to prevent disease and prepare the plant for dormancy.
Regardless of whether the plant is destined to be saved or disposed of, the main stems should be cut back to a height of approximately four to eight inches above the ground. This deliberate pruning reduces the amount of decaying foliage that could harbor fungal diseases or attract overwintering pests. Leaving a short section of stem helps mark the plant’s location and provides a small measure of protection for the crown, which is the point where the stems meet the roots. This action redirects the plant’s energy reserves down into the root system, which is where it is needed for survival over the cold season.
Overwintering Methods for Perennial Mums
For gardeners aiming to keep their hardy mums, the focus shifts entirely to protecting the root ball from the harsh effects of winter. The most significant threat to a perennial mum’s survival is not sustained cold, but rather the repeated cycle of freezing and thawing that can heave the plant out of the soil and damage the crown. Effective overwintering techniques depend on whether the plant is in the ground or a container.
In-Ground Mums
For plants remaining in the garden bed, the crown must be insulated using a heavy layer of organic mulch. A generous covering of six to eight inches of straw, shredded leaves, or pine boughs should be applied shortly after the ground has frozen solid for the first time. Applying the mulch too early can trap moisture and heat, which might encourage new, tender growth that will be instantly damaged by the incoming cold. This insulating layer helps to stabilize the soil temperature and prevent the damaging freeze-thaw cycles that can kill the roots.
Container Mums
Container-grown mums require a different strategy because the root system is more exposed to cold air and is not buffered by the surrounding earth. The best approach is to move the pots to a protected, unheated space, such as a garage or an insulated shed, before the first hard freeze. The ideal storage environment is a dark area where the temperature consistently remains between 32 and 50 degrees Fahrenheit, allowing the plant to remain dormant without freezing solid.
During their time in storage, it is important to check the potted mums occasionally to ensure the roots do not completely dry out. While the plant is dormant and not actively growing, it still requires a small amount of moisture to sustain the root cells. Watering sparingly, perhaps once a month, is usually sufficient to prevent desiccation. The plants can be returned to the outdoors in the spring once the threat of severe frost has passed and new growth begins to emerge.
Disposal and Sanitation
Once the stems have been cut back, the resulting debris must be handled with sanitation in mind, particularly if the plant material shows signs of disease or pests. Plant matter that appears healthy, consisting only of spent blooms and green or browned stems, can generally be added to a home composting system. This material will break down over time and contribute valuable organic material to the soil.
However, any foliage or stems that exhibit discoloration, spots, mildew, or signs of insect infestation should never be placed in a backyard compost pile. Most home composting setups do not reach the sustained high temperatures, typically between 130 and 150 degrees Fahrenheit, required to effectively kill persistent pathogens, such as fungal spores or bacteria. Introducing diseased material risks spreading those problems back into the garden when the finished compost is used.
For safety, all diseased or pest-ridden plant parts must be bagged securely and disposed of in the household trash or through a municipal yard waste service that uses high-temperature processing. If the mum was treated as an annual, the entire root ball and remaining crown can also be disposed of this way. Proper sanitation prevents the carryover of disease, ensuring that future plantings remain healthy.