Chrysanthemums, commonly known as mums, signal the arrival of fall with their vibrant colors in garden centers and on porches across the state. Michigan gardeners often wonder if these plants can survive the harsh winter and return the following year. The answer is not a simple yes or no, as survival depends entirely on the mum’s variety and the specific care it receives before the ground freezes. Understanding the differences between mum types and employing certain cultivation strategies are necessary for success in a cold climate.
The Mums of Michigan: Annual or Perennial?
Most true garden chrysanthemums (Chrysanthemum morifolium) are classified as herbaceous perennials. Michigan falls within USDA Hardiness Zones 4 through 6, a range where these plants are technically hardy enough to survive the winter. However, survival is conditional and often fails due to a lack of root establishment before the deep freeze sets in.
For a mum to be a successful perennial, it must develop a robust root system and produce underground runners called stolons. These stolons allow the plant to regenerate in the spring. Mums purchased in full bloom during autumn are typically focused on flowering, not root growth.
Planting in late September or October does not allow the roots sufficient time to anchor and store energy before the ground freezes solid. Consequently, the plant is frequently treated as a disposable annual because it fails to survive the first winter. True perennial success in Michigan demands proper planting timing.
Distinguishing Hardy Garden Mums from Florist Varieties
The most important step for perennial success is choosing the right type of plant. The varieties commonly sold at grocery stores, florists, or big-box retailers in small decorative pots are typically “florist mums” or “pot mums.” These are bred for maximum bloom density and visual impact but not for winter survival.
Florist mums exhibit a dense, mounding growth habit, where the foliage is often completely obscured by flowers. Their root systems are shallow and compact, making them ill-equipped to handle freezing soil temperatures. Since they are not intended to survive temperatures below USDA Zone 7, their return in Michigan is highly unlikely.
In contrast, hardy garden mums are developed for perennial performance, often found in the perennial section of a garden center. These varieties have a looser, more sprawling growth habit, with more visible green foliage between the flowers. Hardy mums are bred to develop the deep root structure and stolons needed to survive cold winters.
Overwintering Techniques for Cold Climates
For hardy mums to thrive in Michigan, attention to planting time and environment is paramount. The single most important factor for success is planting the mum in the ground by late summer, ideally July or August. This early timing provides the weeks necessary for the roots to grow outward and establish the energy reserves needed to endure winter dormancy.
Location is equally critical, requiring a site that receives full sun and, most importantly, has excellent drainage. Mums are not typically killed by the cold itself but by the freeze-thaw cycle and overly saturated soil, which causes ice to form around the crown and roots. Planting in a wet, low-lying area will guarantee the roots rot or are damaged by ice.
Once the mum has finished blooming and hard frosts have turned the foliage brown, prepare for winter with caution. Avoid cutting the dead stems and foliage down to the ground immediately after flowering. Leaving the top growth intact helps collect insulating snow and directs water away from the plant’s crown, preventing rot.
After the ground has completely frozen solid, apply a layer of loose, airy mulch around the plant. Use materials like straw, pine needles, or shredded leaves, forming a protective blanket four to six inches deep. This layer stabilizes the soil temperature and prevents frost heaving, which is the repeated rising and falling of the soil that tears the mum’s shallow roots. The old stems can then be cut back to about three to four inches above the soil line, and the mulch should be removed carefully in early spring when new green growth appears.