Chrysanthemums (mums) are the quintessential flower of autumn, providing a vibrant burst of color when most other garden plants fade. Whether these popular plants can survive a frost depends primarily on the variety and the severity of the cold event. Mums are known to be tolerant of cooler temperatures but are not universally frost-resistant. A sudden drop below freezing can cause damage or even death to less hardy types. Understanding the specific nature of your chrysanthemum is the first step in ensuring its longevity through unexpected cold snaps.
Understanding the Types of Mums and Hardiness
A chrysanthemum’s ability to withstand freezing temperatures is determined by its classification: the hardy garden mum or the more tender florist mum.
Hardy Garden Mums
Hardy garden mums, also known as perennial mums, are bred to survive winter dormancy, typically thriving in USDA hardiness zones 5 through 9. These varieties possess robust, established root systems that can tolerate ground temperatures dropping to around 20°F (-6°C) when properly insulated. While the flowers and foliage may be damaged by frost, the plant’s crown and roots are designed to survive and regrow the following spring.
Florist Mums
Florist mums, often sold in pots for temporary seasonal display, are far more sensitive to cold. These plants are generally grown as annuals and lack the winter hardiness of garden varieties, possessing shallower root systems. A light frost (30°F to 32°F) can cause minor cosmetic damage to their blooms and leaves. However, a hard freeze (below 28°F for several hours) will likely collapse the stem tissue and kill the entire plant.
Quick Steps for Protecting Mums from Unexpected Frost
When a sudden drop in temperature below 32°F (0°C) is predicted, immediate protective action is necessary. One effective pre-frost measure is ensuring the soil around the mum is adequately moist. Watering the plant thoroughly before a freeze helps, as wet soil retains heat more efficiently than dry soil, slowly releasing warmth overnight to the root zone.
Protecting Container Mums
For potted florist mums or any vulnerable container plants, the simplest solution is to move them temporarily to a sheltered location. An unheated garage, shed, or covered porch provides sufficient thermal protection to shield the plant from the direct impact of frost.
Covering In-Ground Mums
For in-ground mums, covering them is the best defense. Use a breathable material like a bed sheet, burlap, or frost-protection fabric, which can offer protection down to about 25°F (-4°C). The covering should be draped loosely over the plant, extending to the ground to trap residual warmth radiating from the soil. Avoid using plastic sheeting directly on the foliage, as it conducts cold and can damage the leaves where it touches them. Remove the covering the following morning after the sun has risen and temperatures have climbed above freezing to prevent overheating.
Recovery and Care After a Frost Event
After a frost, the initial assessment of damage is important, but gardeners should resist the urge to prune immediately. Frost-damaged foliage, which often appears blackened, wilted, or mushy, should be left in place. This dead material acts as an insulating layer, providing protection for the plant’s crown and roots against subsequent cold snaps.
If only the flowers and upper leaves are damaged, the crown and roots are likely still viable, especially on hardy garden varieties. Damage to the plant’s core is indicated by soft, mushy stems near the base, signaling that the internal tissue has ruptured from freezing. For the less hardy florist mums, recovery is unlikely, and they are typically discarded after significant frost damage.
Preparing Hardy Mums for Winter
For hardy mums, prepare the plant for long-term winter dormancy by adding a 2- to 4-inch layer of light, airy mulch, such as straw or pine needles, around the base once the ground has begun to freeze. This mulch insulates the roots and helps prevent damaging freeze-thaw cycles that can cause the soil to heave and expose the roots. Pruning should be delayed until the following spring. When new growth emerges, the old, dead stems can be cut back to just a few inches above the soil line.