The vibrant blooms of chrysanthemums, or mums, are a defining characteristic of the autumn landscape. Often purchased as temporary seasonal decorations, these plants are herbaceous perennials that can return year after year with proper care. The goal in saving a mum is transitioning it from a late-season display to an established perennial garden feature that can successfully survive winter dormancy. Success hinges on recognizing the difference between cold-tolerant hardy garden varieties and the more tender florist mums, which are not bred for winter survival.
Preparing Mums for Dormancy
Preparation for overwintering begins immediately after the peak of the autumn bloom. It is important to distinguish between hardy garden mums, which have smaller flowers and are sold as perennials, and florist mums, which feature larger blooms and are often treated as annuals due to their limited cold hardiness. The key is to encourage the plant to divert its remaining energy toward root establishment rather than seed production, improving its chances of surviving the cold months.
This is achieved through deadheading, where you remove the spent flower heads. Preventing the plant from setting seed signals the plant to channel resources into developing a stronger root mass before the ground freezes. Once the foliage has browned and wilted, indicating dormancy, cut back the stalks. For in-ground mums, use clean shears to trim the entire plant down, leaving about four to six inches of stem growth above the soil line.
This remaining stubble helps protect the crown and provides a visual marker for its location during winter. Removing the dead foliage minimizes the habitat for overwintering pests and fungal diseases. Continue to provide adequate water until the first hard freeze, ensuring the soil is moist but never waterlogged, which is a common cause of root rot.
Overwintering Strategies for Survival
Protecting the dormant mums from winter weather fluctuations is the most significant step in ensuring their return. For hardy garden mums planted in the ground, the primary threat is the cycle of freezing and thawing. This cycle can cause the plant’s shallow root system to heave out of the soil, exposing the vulnerable roots to drying winter winds and fatal temperatures.
To combat this, apply a thick layer of organic mulch, such as straw, shredded leaves, or pine needles, to the base of the plant. This mulch layer should be six to eight inches deep and must only be applied after the ground has frozen solid. Applying the mulch too early can trap heat, delaying dormancy and encouraging premature new growth susceptible to sudden freezes. Proper site drainage is also essential, as saturated soil can lead to the decay of the crown and roots during the winter months.
Florist mums, or any mums remaining in containers, require a different approach due to their reduced cold tolerance. These potted plants should be moved to a protected, unheated location once the foliage has died back and before sustained freezing temperatures arrive. An unheated garage, shed, or cool basement that maintains temperatures just above freezing, ideally between 32 and 50 degrees Fahrenheit, is suitable. The goal is to keep the plant in sustained dormancy.
While in storage, the mums do not require light, but they need occasional moisture to prevent the root ball from desiccating. Check the soil once a month and provide a small amount of water if it is completely dry. Keep the soil barely moist, not saturated, to avoid encouraging mold or active growth. Place the pots on blocks or a pallet to ensure air circulation beneath them, reducing the risk of rot.
Spring Revival and Ongoing Health
The transition out of winter dormancy requires careful timing to avoid late-season frosts. Once the threat of hard frost has passed and green growth emerges from the base of the plant, safely remove the heavy winter mulch from in-ground mums. Potted mums should be gradually acclimated to outdoor conditions by moving them to a sheltered, partially shaded spot for a week before placing them in their final sunny location.
Spring is the time for dividing older, established clumps, a practice that maintains plant vigor and prevents the center of the mum from becoming woody. Every two to three years, use a sharp spade to dig up the entire clump and separate the healthy new growth around the outside edges. Replant only these vigorous outer divisions, discarding the old, central core.
As new growth reaches approximately six inches in height, begin the “Pinch Back” technique. This method involves removing the top one inch of each new stem to encourage lateral branching. This action forces the plant to develop a dense, bushy form rather than a tall, leggy structure, which leads to a greater number of fall blooms.
Repeat this pinching every two to four weeks, or after every six inches of new growth, stopping by mid-July. This deadline allows enough time for the plant to set its flower buds for the autumn display. As the plant begins its active growth phase, apply a balanced, slow-release granular fertilizer or a liquid feed to support the developing foliage and root system. Monitor the emerging leaves for common garden pests, such as aphids, and address any infestations immediately.