Chrysanthemums, commonly known as mums, are a signature flower of the autumn season, providing vibrant color as other blooms fade. Whether these plants are perennial or annual does not have a single, straightforward answer. The outcome depends on two primary factors: the specific chrysanthemum variety purchased and the winter conditions of the local climate. Understanding these distinctions is necessary for any gardener hoping to see their mums return year after year.
Understanding Hardiness and Climate Zones
A plant’s life cycle is defined by its ability to survive the winter, which is tied to its genetic hardiness and the local climate. A perennial plant lives for more than two years, typically dying back to the ground in winter only to regrow from the same root system in spring. Annuals, conversely, complete their entire life cycle within a single growing season and must be replanted each year.
The ability of a mum to function as a perennial is determined by the minimum sustained temperature it can tolerate, mapped out by the USDA Hardiness Zones. Most perennial mums are reliably hardy in zones 5 through 9, where winter temperatures generally do not dip below -20 degrees Fahrenheit. Within these zones, the plant’s underground structures can survive dormancy and regenerate new growth.
However, even a genetically perennial mum may behave like an annual if planted in an area colder than its rating or if it lacks sufficient root establishment before the ground freezes. It is often the cycle of freezing and thawing that can heave the shallow root system out of the soil or cause root rot. Therefore, a mum’s perennial status is relative to the environmental context.
Differentiating Garden and Florist Varieties
The most important step in predicting a mum’s survival is identifying its variety, as chrysanthemums are separated into two commercial categories. “Garden Mums,” often referred to as hardy mums, are specifically bred to survive the winter. These cultivars develop a robust, deep root system and produce underground shoots, called stolons, which store energy and allow the plant to regenerate after a hard frost.
Garden mums are typically sold at nurseries and garden centers, sometimes in the spring, which gives them a full season to establish their roots before winter. They feature a less dense, more open growth habit and are often marketed by their specific variety names. If a mum is intended to be a perennial, it will usually be labeled with its hardiness zone rating.
“Florist Mums” are the dense, ball-shaped plants commonly sold at grocery stores and seasonal stands in the fall. They are cultivated to produce a massive flush of compact, uniform blooms for decorative purposes. This aggressive cultivation prioritizes flower display over root development, resulting in a shallow, less vigorous root system poorly equipped to survive freezing temperatures.
Florist mums, also called pot mums, are essentially treated as annuals, intended to provide temporary color before being discarded. They lack the deep root structure and sufficient energy reserves to reliably withstand a typical winter. Attempting to overwinter a florist mum is often unsuccessful because their breeding and shallow root growth make them highly susceptible to cold soil and moisture fluctuation.
Essential Steps for Overwintering Success
For a hardy garden mum to survive the winter, its roots must be well-established before the ground freezes solid. The best practice is to plant the mum in the ground during the spring or early summer, allowing at least six weeks of root growth before cold weather arrives. Fall-purchased mums should be planted as early as possible to maximize establishment.
Once the plant has finished flowering and the first hard frosts have occurred, a deep layer of organic mulch must be applied. This protective layer, ideally six to eight inches of straw, shredded leaves, or pine needles, should be placed around the plant’s crown after the soil has completely frozen. The mulch serves to insulate the ground and prevent damaging freeze-thaw cycles.
Delay pruning the dead or dried foliage until the following spring. The old stems and leaves act as additional natural insulation, protecting the plant crown from extreme cold and wind. When new growth begins to emerge from the base in the spring, the old stems can then be cut back cleanly to ground level.