Chrysanthemums, commonly known as mums, are celebrated for their vibrant autumn displays, offering a welcome burst of color when most other garden plants fade. While they are often purchased and treated as annuals, many varieties are perennial and can survive multiple seasons with the proper care. Successfully overwintering these plants ensures they return year after year, providing reliable fall color. The process involves specific steps to induce dormancy and protect the root system from damaging freezing temperatures.
Preparing Mums for Winter Dormancy
The preparation process begins in late summer or early fall, long before the first hard frost arrives, when the plant naturally slows its growth cycle. Gardeners should stop applying nitrogen-heavy fertilizers by late August to allow the plant tissues to harden off before the cold sets in. Continued fertilization encourages tender new growth that is highly susceptible to freezing damage and subsequent cellular destruction.
Once the flowers have faded and the foliage begins to brown, the stems should be cut back to signal the plant to enter its dormant phase. It is generally recommended to leave approximately one to six inches of stem above the soil line, with two to three inches being a common target for in-ground plants. This remaining short length provides a small measure of protection for the crown and makes the plant easier to locate under any protective covering.
Before the ground freezes solid, ensure the plant is well-hydrated, as dry soil intensifies the effects of cold on the roots. Water deeply one final time to help insulate the root ball, but avoid standing water that could lead to crown rot. Clearing away dead leaves or spent debris from the base of the mum eliminates hiding places for pests and fungal spores.
Choosing the Right Overwintering Method
The method for successful overwintering depends primarily on the plant’s hardiness and whether it is planted in the ground or kept in a container. Hardy varieties planted in the ground in zones 5 through 9 have a better chance of survival, especially if they were planted in the spring and had time to establish an extensive root system. In these situations, protection should be applied only after the soil surface has frozen solid, which prevents premature sprouting.
Place a thick layer of insulating material, ideally three to eight inches deep, over the crown and root zone. Materials such as straw, pine needles, or shredded hardwood bark are effective. They create air pockets that provide insulation without compacting the soil, allowing the plant to breathe and preventing moisture buildup that leads to fungal issues.
Non-hardy varieties or potted mums require relocation to a sheltered environment, such as an unheated garage, shed, or cold cellar. The ideal storage temperature is just above freezing, between 32 and 50 degrees Fahrenheit. This range keeps the plant dormant without allowing the root ball to freeze completely, which causes cellular damage.
During cold storage, plants require minimal light and infrequent watering. The goal is to prevent the root ball from desiccating, which would kill the plant. A light watering once every few weeks is sufficient, ensuring the soil barely retains moisture. Placing pots on a raised surface prevents direct contact with cold concrete floors, which draw heat away from the roots.
Spring Revival and Care
The transition out of dormancy in the spring must be gradual to prevent shock. For in-ground mums, remove protective mulch slowly as the threat of severe frost diminishes. Removing the covering gradually over several days allows the plants to acclimate to fluctuating temperatures and increasing light levels.
Potted mums stored indoors should be moved back outside to a sheltered, partially shaded area after the last anticipated hard frost. This gradual exposure, called hardening off, helps acclimate the new growth. Cut back any remaining old, woody stems completely to the ground level just as new green shoots appear.
This final pruning directs the plant’s energy into vigorous new growth from the root crown, creating a fuller plant. Once new foliage is established and reaches approximately six inches in height, apply a balanced, slow-release fertilizer to support the season’s growth.