An agent for preventing coloration irregularities in a flowering plant, the agent having as an active ingredient the jasmonate represented by general formula (1) (in the formula, R1 represents a pentyl group or a pentenyl group, and R2 represents a hydrogen atom or a C1-6 alkyl group), and a method for preventing coloration irregularities in a flowering plant, in which the jasmonate is applied to cut flowers. According to the present invention, it is possible to cause a cut flower harvested at the budding stage to bloom without generating coloration irregularities.