Chrysanthemums, commonly known as mums, are a signature flower of autumn, providing a burst of color when most other plants are fading. A plant is considered “hardy” if it can withstand the average minimum winter temperatures of a specific region and emerge from dormancy in the spring. While many mums are sold as temporary seasonal decorations, certain varieties are true perennials with the potential to survive winter and bloom again. Understanding this distinction is the first step toward ensuring your plants endure the cold.
Garden Mums Versus Florist Mums
Confusion about a mum’s hardiness stems from the difference between the two main types sold commercially: garden mums and florist mums. Garden mums, also called hardy mums, are perennial varieties specifically bred for cold tolerance and survive winters in USDA Hardiness Zones 5 through 9. These plants are bushy with a spreading growth habit, displaying a balanced mix of foliage and flowers. Hardy mums develop underground shoots, known as stolons, which allow them to overwinter and return each spring.
Florist mums, or pot mums, are frequently found at stores and seasonal displays and are treated as annuals. They are cultivated in greenhouses to produce an abundance of large, showy flowers that often obscure the foliage. This forcing process prevents them from developing a robust root system, leaving them ill-equipped for winter survival. These mums lack the cold-hardiness and energy reserves needed to persist through freezing temperatures. When purchasing mums, selecting a plant with more visible foliage and a less dense, natural shape suggests it is a hardy garden variety.
Environmental Conditions That Impact Survival
A mum’s potential for winter survival, even for a hardy variety, is determined by the environment and timing of planting. The USDA Plant Hardiness Zone Map classifies regions based on their average annual minimum winter temperature. Hardy mums are rated for specific zones, and planting a mum outside of its designated zone significantly reduces its chances of survival.
Timing is crucial because mums are shallow-rooted plants. Hardy mums must be planted early enough to develop an established root system before the ground freezes solid. Planting a perennial mum in late fall forces the plant to expend energy on blooming rather than root growth, reducing the resources needed for winter dormancy. Ideally, garden mums should be planted in the spring to allow the entire growing season for establishment. However, planting at least six weeks before the first hard frost offers a decent chance of survival. Repeated freeze-thaw cycles in the soil can also physically push the shallow roots out of the ground, a process called heaving, which damages or kills the plant.
Preparing Mums for Winter Dormancy
Successful overwintering of established, hardy garden mums requires care to protect the crown and roots from cold and moisture. Unlike many perennials, it is best to leave the dead foliage and stems intact after the blooming season finishes. The old growth helps insulate the plant’s crown and traps snow, protecting the plant from severe cold. Pruning the stems down to six to eight inches can be done, but cutting them to the ground before winter removes this protective layer.
Mulch application stabilizes the soil temperature and prevents the damaging freeze-thaw cycles that cause heaving. Once the soil has frozen completely, apply a thick layer of loose, organic mulch, such as straw or pine needles, three to four inches deep over the plant’s crown and surrounding soil. Avoid using leaves, which can mat down, trap too much moisture, and lead to rot. Ensure the mulch is not pressed directly against the base of the stems, which can encourage moisture retention and potential disease.
Maintaining consistent soil moisture before the ground freezes is also necessary for preparing mums for dormancy. Plants must be well-hydrated to survive the winter, as dry soil can worsen the effects of cold damage. Continue watering regularly until the soil is no longer workable, ensuring the roots are fully saturated before the deep freeze sets in. Once the ground has frozen solid and the mulch is in place, the plant will remain dormant until the following spring.