Overwintering Mums

Garden mums (Chrysanthemum x morifolium) are known for their vibrant blooms and resilience and are a popular choice for adding color to gardens and landscapes in the fall. While they are typically hardy in zones 5 to 9, individual cultivars can vary in cold tolerance because of their complex genetic makeup. Winter survival may also vary with location, culture, site, or winter severity. Because of these reasons, they are no longer typically called hardy mums, but garden mums.  Florist mums (also Chrysanthemum x morifolium) are not bred for hardiness and therefore are not hardy when subjected to freezing. 

Garden mums are versatile plants that can typically survive our winter conditions here in Virginia. Still, they need the right care to make it through the colder months. To ensure these perennials thrive and come back strong each year, proper winter care is essential.  

To ensure good root development for your garden mum, it likely needs to be planted in the ground/garden in late August or early September.  Early planting helps ensure the root development that is required before the ground freezes.  The problem with this timing is that often garden mums are not blooming at this time of the year, and therefore they are not typically available for sale.  You may want to enjoy the plant in a decorative container while it is flowering and not necessarily in a garden bed until after it is done blooming, which will be late September into October.  Just understand that the later the mums are planted, the lower the survival rate.  A late-planted mum will not develop a good root system in the garden soil.  Because of the short-day conditions of the fall, mums are naturally programmed to be flowering at this time of the year, not producing roots.   

If the mums successfully overwinter, to ensure proper growth the next year, make sure that they are planted in an area that will receive 6 or more hours of direct sunlight.  Remember that a sunny spot in fall might not receive enough light in summer when trees have leaves.

Freezing and thawing of the soil during the winter can cause the plant to heave, exposing its roots to drying winds.  This increases the chance of death to perennials.  The earlier you plant your mums, the less chance of heaving because the plant has had a chance to root into the existing soil. 

This first year, leave the existing foliage and stems on the plant until after the first hard frost. The material helps provide insulation against harsh winter conditions.  You will also need to add 3-4 inches of light, airy mulch over the crown of the plant.  This mulch can be pine needles, loose shredded bark, clean straw (not hay), or evergreen branches.  The loose mulch settles through the mum branches, protecting them from winter winds and shading the soil.  This discourages alternate freezing and thawing of the soil. These protective mulches may be removed or pulled away from the crown of the plants by early- to mid-April after the danger of severely cold weather has passed.

An alternative to planting this fall is to keep the plant protected while still in its original container.  You can move the plant to a cold frame or greenhouse structure.  You can also keep the plant in the corner of an unheated basement or insulated garage where it will not freeze. 

Continue watering your mums until the first hard frosts, then gradually reduce watering as winter approaches. Garden mums require less water during their dormant period. It may also be that you don’t have to water if we get enough rain or snow.  Pay attention to the weather patterns.  You also don’t want the plant to be completely dry.  The dry soil will allow the cold air to into the soil profile increasing the chances of heaving.  On the flip side, make sure that your mums are planted in a well-draining location. Heavy, waterlogged soil can be detrimental during the winter months 

Proper winter care is crucial for ensuring that your hardy mums survive the colder months and come back looking vibrant in the spring. By following these tips—such as planting early, applying mulch, adjusting watering practices, and protecting against severe weather—you can help your mums endure winter and continue to provide beautiful blooms for years to come.

With a little preparation and care, your hardy mums will reward you with their stunning displays of color every fall.