Chrysanthemums are shallow-rooted plants. Repeated freezing and thawing of the soil during the winter months can heave plants out of the ground and cause severe damage or even death.
Gardeners can increase the odds of their mums surviving the winter by applying a mulch in fall. Mulching helps eliminate the alternate freezing-thawing cycles that can heave plants out of the soil. Apply the mulch in late fall, typically late November/early December in central Iowa. Do not cut back the plants prior to mulching. Simply cover the plants with several inches of mulch. Suitable mulching materials include clean straw, pine needles, and evergreen branches. Leaves are not a good mulch as they tend to mat down and don't provide adequate protection. The mulch should remain in place until early to mid-April.