Chrysanthemums, commonly known as mums, provide vibrant color to gardens in autumn as other plants fade. These flowers are popular for their late-season blooms, but their ability to withstand cold weather and survive the winter often confuses people. How long a mum lasts depends on the specific variety and the steps taken to prepare it for dormancy. With proper care, certain types of mums can return year after year, becoming a hardy perennial plant.
Understanding the Difference Between Mum Varieties
The lifespan of a chrysanthemum is primarily determined by whether it is a “Florist Mum” or a “Garden Mum.” Florist mums are typically sold at grocery stores and florists, cultivated for maximum visual appeal with little regard for winter hardiness. These varieties are generally treated as tender annuals, expected to last only one season. They possess shallow root systems ill-equipped to handle freezing temperatures and the soil’s freeze-thaw cycles.
In contrast, Garden Mums, also called hardy mums, are perennial varieties bred to survive winter in the ground, generally in USDA Zones 5 to 9. These plants develop underground shoots, known as stolons, which aid in perennial survival. For garden mums to successfully overwinter, they must be planted early in the season, ideally in spring or early summer. This allows their root systems ample time to establish before the first hard frost. Fall-purchased garden mums often struggle because they lack the robust root growth needed for winter defense.
Strategies for Overwintering Mums Outdoors
Mums planted directly into the garden soil have the best chance of returning, provided they are hardy varieties given adequate preparation. Ensuring excellent water drainage is crucial for outdoor survival, as frozen, waterlogged roots are more damaging than the cold itself. Choose a well-drained location protected from strong winter winds to minimize plant stress.
Once the foliage has died back after a few hard frosts, leave the dead stems intact rather than cutting them immediately. The old growth acts as natural insulation, trapping snow and protecting the plant’s crown from extreme temperature fluctuations. After the ground freezes solid, apply a thick layer of protective mulch, such as pine needles, straw, or evergreen boughs, around the plant’s base. This heavy layer, often three to four inches deep, keeps the ground consistently frozen, preventing damaging cycles of thawing and refreezing.
How to Store Potted Mums During Dormancy
Mums remaining in containers, a common situation for late-season purchases, are highly vulnerable to freezing and require protected storage. Container plants are far more susceptible to root damage because their entire root ball is exposed to ambient air temperatures. To prepare a potted mum for dormancy, cut the plant back to about four to six inches above the soil line after the blooms have faded.
The container must then be moved to a cool, protected, and dark location, such as an unheated garage, shed, or cold cellar. The ideal storage temperature is just above freezing, between 32°F and 50°F, which encourages dormancy. During this dormant period, the mum requires very little moisture. Check the soil monthly and water sparingly, just enough to prevent the roots from completely drying out. Overwatering is a common mistake that leads to root rot.
Spring Care and Rejuvenation
As the threat of hard frost passes in early spring, both in-ground and stored mums need careful attention to encourage new growth. For plants overwintered in the garden, gradually remove the heavy protective mulch to allow the soil to warm and new shoots to emerge. Prune away any remaining dead stems and foliage from the previous season to tidy the plant and make way for fresh growth.
Potted mums stored indoors should be gradually acclimated to the outdoors, starting with short periods in a sheltered, shaded location. Once new growth is visible, regular watering can resume, and a balanced fertilizer may be applied to support the initial growth spurt. To ensure a full, bushy plant with numerous blooms in the fall, the practice of “pinching” must be performed. Pinching involves removing the top inch or two of new stem growth, which stimulates the production of multiple side shoots. Repeat this process several times until early to mid-summer, stopping then to allow the plant to set its flower buds for the autumn display.