From our perspective, survival is a complex interplay of genetics and environmental response. We, chrysanthemums, are predominantly herbaceous perennials. This means that while our above-ground stems and foliage are tender and will succumb to a hard freeze, our root systems possess a latent vitality. Our primary strategy is to enter a state of dormancy. As temperatures drop and daylight wanes, we cease vegetative growth and redirect our remaining energy downward, storing precious carbohydrates in our roots and crown (the base of the plant where stems meet roots). This stored energy is the lifeline that will fuel new growth when favorable conditions return in spring.
Your location, defined by its USDA Hardiness Zone, is the most critical factor determining our fate. This zone map is essentially a guide to the average annual extreme minimum winter temperature. Our ability to survive winter is directly tied to these average lows. Many common garden mums (Chrysanthemum × morifolium) are only reliably winter hardy in Zones 5 through 9. In Zone 5, this means we can typically withstand temperatures down to -20°F to -10°F, but only with adequate protection. If you are in Zone 4 or below, the extreme cold can kill our root systems, making survival unlikely without being treated as an annual or provided with exceptional, specialized protection.
Even within a suitable zone, winter presents multiple threats beyond simple cold. Our greatest enemy is not consistent cold, but fluctuating temperatures that cause a cycle of freezing and thawing. This action can heave our root systems right out of the soil, exposing them to desiccating winds and killing cold. Furthermore, winter sun and wind can cause excessive moisture loss from our evergreen leaves (on some varieties) and stems, a condition known as desiccation. Perhaps most dangerously, wet soil combined with freezing temperatures is often fatal. Our roots require well-drained conditions; sitting in frozen, waterlogged soil will lead to rot and certain death.
You can greatly enhance our natural survival mechanisms through mindful care. The most important step begins long before winter; ensuring we are planted in well-draining soil is non-negotiable. Do not cut our stems back in fall. Leaving the dead foliage intact creates a natural insulating layer that traps air and protects our crown. After the ground has frozen hard, applying a thick, loose mulch of straw, shredded leaves, or evergreen boughs around 4 inches deep over our base is invaluable. This mulch regulates soil temperature, prevents heaving, and retains moisture. Please avoid using heavy, matting mulches like whole leaves, which can suffocate us. Finally, ensure we enter winter well-hydrated by providing deep waterings in late autumn before the ground freezes.
