Chrysanthemums, or “mums,” are the quintessential flower of the fall season, celebrated for their vibrant, late-season color. Whether a mum is a perennial depends entirely on the specific variety purchased and the care it receives. Mums are botanically capable of being perennials, but commercial breeding and cultivation practices have created a significant difference in hardiness between the two types most commonly sold. Understanding this distinction is key to ensuring these beautiful flowers survive the winter and return.
Understanding the Difference Between Garden and Florist Mums
Mums are categorized into two main groups that dictate their perennial viability: the hardy garden mum and the decorative florist mum. Both types belong to the same species, Chrysanthemum x morifolium, but they are bred for completely different purposes. Garden mums, often labeled “hardy mums,” are specifically developed to be winter-tolerant and capable of surviving outdoors year after year.
These garden varieties are typically hardy in USDA Zones 5 through 9. They produce underground shoots called stolons that help establish a robust root system capable of withstanding freezing temperatures. Florist mums are bred for appearance, producing a dense, ball-like mass of flowers with very little visible foliage. These decorative plants are often forced into bloom for fall sales, resulting in a shallow, underdeveloped root system.
Florist mums are generally intended to be treated as annuals, enjoyed for their seasonal display, and then discarded. Even in warmer regions (Zones 7 to 9), their lack of a deep, established root system means they have a low survival rate through the winter. A chrysanthemum’s perennial status is less about its genetics and more about its cultivation—whether it was bred for showy blooms or for winter hardiness.
Environmental Factors for Perennial Success
For a hardy garden mum to return, it must be planted in an environment that allows its root system to fully develop and survive winter dormancy. The plant must be a variety rated for the gardener’s specific USDA hardiness zone, which defines the average minimum winter temperatures. Mums thrive in locations that receive at least six hours of direct sunlight daily, as this energy is necessary for building the reserves needed to survive the cold season.
The most significant environmental factor for winter survival is soil drainage. Chrysanthemum roots quickly rot if left in consistently wet or soggy soil, especially during the cold, dormant months. Good drainage is paramount, and heavy clay soil should be amended with organic matter to improve its structure before planting.
Timing is crucial for perennial success, as mums purchased in the fall are often focusing their energy on blooming rather than root growth. Hardy mums should ideally be planted in the spring or early summer, giving them the entire growing season to establish a deep, extensive root system before the ground freezes. Fall-planted mums have a significantly lower survival rate because they do not have enough time to anchor themselves against the freeze-thaw cycles that can push plants out of the ground, a phenomenon known as frost heaving.
Essential Care for Winter Survival
Even the hardiest varieties require specific preparation for winter. After the blooms have faded and the foliage has been killed by a hard frost, the stems should be left standing. The remaining dead foliage acts as a natural layer of insulation, helping to protect the plant’s crown from the cold.
Pruning should be delayed until new growth is visible in the spring, at which point the old, dead stems can be cut back to the ground. A thick layer of insulating mulch is important for protecting the plant’s crown from temperature fluctuations. This mulch, consisting of materials like straw, pine needles, or chopped leaves, should be applied around the base of the plant after the soil has completely frozen.
Applying a four to six-inch layer of mulch after the ground has frozen keeps the soil consistently cold, preventing repeated freezing and thawing that causes frost heaving. Once winter has set in, established mums do not require additional watering. They should be kept relatively dry, as excessive moisture combined with cold is a primary cause of root rot during dormancy.