Spring is the best time to plant garden mums in Iowa, according to horticulturists with Iowa State University Extension and Outreach. Chrysanthemums are photoperiodic, meaning they bloom based on the length of the day. Garden mums in Iowa bloom in early fall, as the days get shorter. By planting them in spring, they have time to grow and establish themselves before blooming. When planting, garden mums should be placed in full sun and early spring is the best time to divide mums.
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