Chrysanthemums, commonly called mums, are a popular choice for adding a burst of color to the late-season landscape. These plants are celebrated for their diverse flower forms and rich autumn hues. Whether a mum can survive the winter outdoors depends largely on its variety and the planting techniques used. Understanding the difference between plant types and following specific care instructions are necessary steps for establishing mums as a long-term fixture in the garden.
Understanding Perennial Versus Annual Mums
The confusion about winter survival stems from the two primary types sold commercially. Varieties typically found at florists are “florist mums,” bred for large, showy blooms and treated as annuals in most regions. These decorative varieties lack hardiness and have shallow root systems, making them ill-equipped to handle prolonged freezing temperatures.
Mums intended for garden beds are “hardy mums” or “garden mums,” which are true herbaceous perennials capable of surviving winter dormancy. These hardy cultivars are generally reliable in USDA Hardiness Zones 4 through 9, though some specialized varieties survive in zone 3. Garden mums are specifically bred to form a robust root crown that withstands the freeze-thaw cycles of winter. When purchasing, look for labels that specifically state “hardy” or “perennial.”
A hardy mum’s ability to return each spring is tied to its capacity to establish a strong root system before the ground freezes solid. If planted too late in the fall, even a hardy variety may not develop enough underground growth to survive its first winter. Deep root establishment is the most important factor for long-term perennial success.
Proper Techniques for Planting Mums Outdoors
Successful outdoor planting requires selecting the right time. Although mums are often purchased in autumn, spring planting is ideal for establishing them as perennials. Spring planting allows the entire growing season for roots to expand and anchor the plant before winter stress. If planting in the fall, place the mum in the ground at least six to eight weeks before the first anticipated hard frost to allow root development.
The location should receive full sun, meaning a minimum of six hours of direct sunlight daily. Mums require soil that is consistently moist but drains well; saturated ground quickly leads to root rot. If the native soil is heavy clay, amend it with organic matter like compost to improve aeration and drainage. Mums thrive in a slightly acidic to neutral soil pH (6.0 to 8.0).
When planting, remove the mum from its container and gently loosen any tightly bound roots. Dig a hole twice as wide as the root ball but no deeper. Place the plant at the same depth it was in the nursery pot, as planting the crown too deep promotes rot. Backfill the hole with soil, lightly firming it to remove air pockets. Water the mum thoroughly immediately after planting to settle the soil.
Overwintering Care for Long-Term Success
After the blooming season, prepare the hardy mum for dormancy to ensure its survival until spring. It is generally better to delay cutting back old stems until new growth emerges the following spring. The spent foliage acts as natural insulation, protecting the plant’s crown from harsh temperatures and fluctuations. While stems can be cut back to four to six inches for appearance, leaving the bulk of the growth is safer in colder climates.
Protective mulch is an effective measure for successful overwintering. Wait until the ground has frozen solid before applying a thick layer of organic mulch, such as straw or shredded leaves. This layer, applied three to four inches deep, should cover the entire root zone. The mulch maintains a consistent temperature, preventing freeze-thaw cycles that can heave the plant out of the soil.
The mum’s root system needs minimal moisture during winter. In regions with dry winters or inconsistent snow cover, occasional watering may be necessary. Water only during periods of thaw and when the soil is dry, providing just enough moisture to prevent the roots from desiccating. Avoid excessive winter watering, as it can saturate the soil and increase the risk of crown rot.