Garden mums (Chrysanthemum x morifolium) often don't over-winter well in Iowa. 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. Damage is most likely in poorly drained soils.
Home gardeners can increase the odds of their garden mums surviving the winter by protecting them with mulch in fall. Mulches should be applied in late fall after the plants have been exposed to several hard freezes, typically mid- to late November in Iowa. Do not cut back the plants in fall. Simply place several inches of mulch around the mums. Suitable mulching materials include clean, weed-free straw, pine needles, and evergreen branches. Leaves are not a good mulch as they tend to mat down and don't provide adequate protection.
Remove the mulch in early to mid-April and cut out all of the dead material. Those plants that have survived the winter will have green shoots near the ground.
Spring versus fall planting
Garden mums planted in spring survive the winter much better than those planted in fall. Spring planted mums have the opportunity to grow and establish themselves over a period of several months. Fall planted mums have little time to establish themselves before winter and are much more likely to be severely damaged or destroyed.
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