Chrysanthemum Bloom Timing: The Long-Night Requirement

Chrysanthemums are "short-day" plants requiring long nights (12+ hours of darkness) to bloom. Buds form based on temperature and leaf count, but won't open until several weeks of long nights occur. Some cultivars respond faster—hence August vs. October blooms. By early September, nights are ~11.5 hours; plants are on the verge of flowering.