Chrysanthemums (mums) are the defining flower of the autumn garden, providing a burst of color when most other plants are fading. While often treated as annuals, many varieties of garden mums are true perennials that can return year after year with the right preparation. Ensuring their survival through the cold months requires specific timing and attention to detail. Proper winterizing focuses on protecting the plant’s crown and root system from freezing temperatures and moisture.
Timing the Cut
The decision of when to cut back garden mums requires timing that balances insulation with preparation for dormancy. The ideal window for pruning arrives after the plant has finished blooming and the foliage has completely died back, typically following the first hard frost. This frost signals the plant to enter dormancy, stopping the flow of sap and preparing the roots for winter rest.
Cutting back stems too early, while the plant is still actively growing, can stimulate new, tender growth at the base. This fresh growth is susceptible to cold damage and will likely be killed by subsequent freezes, weakening the plant’s crown. Gardeners often choose to leave the dead stalks in place throughout the winter to provide natural insulation for the crown and trap protective snow cover. These stalks can then be removed in early spring before new growth begins.
The Pruning Method
Once the timing is correct, the pruning procedure must be executed with precision and cleanliness to promote plant health. Begin by gathering clean, sharp pruning shears, which minimize damage to the plant tissue and reduce the risk of introducing disease. For chrysanthemums, the cut is a simple reduction of the old top growth to a short stubble.
The goal is to leave the stems standing at a height of four to six inches above the soil line. This remaining stubble marks the plant’s location and offers a small degree of protection to the plant’s crown. Cutting the stems flush with the ground can expose the crown to excessive moisture and temperature fluctuations, increasing the risk of rot.
After the cuts are made, clear away dead or diseased foliage and debris from around the base of the plant. This sanitation step prevents pests, fungal spores, and other pathogens from overwintering in the garden bed and infecting the plant next spring. Removing this organic matter minimizes the chance of crown rot, a common cause of winter failure in perennial mums.
Post-Cut Winter Protection
Pruning is the first part of winter preparation; effective protection of the crown is necessary for successful overwintering. Chrysanthemums possess shallow root systems, making them particularly vulnerable to frost heave. Frost heave occurs when the soil repeatedly freezes and thaws, pushing the plant’s crown and roots out of the ground, resulting in severe root damage and dehydration.
To mitigate this risk, a thick layer of protective mulch should be applied over the cut-back plant, but only after the ground has frozen slightly. Applying mulch too early can trap warmth, encouraging late-season growth that is then killed by the cold. Suitable mulching materials include loose, airy options like straw, shredded leaves, or evergreen boughs, which insulate without becoming compacted.
The mulch layer should be four to six inches deep, covering the plant’s crown and surrounding soil. This covering helps maintain a consistent soil temperature, discouraging the damaging freeze-thaw cycles that lead to heaving. Heavy, water-retaining materials like wood chips or dense compost should be avoided, as they hold too much moisture against the crown and promote rot.