PURPOSE: To obtain a fruiting hormone preparation for melons giving high fruiting yield, a large amount of matured seeds, and fruits of good appearance and high quality, by using a prasinosteroid having an action to control plant growth.

CONSTITUTION: The subject hormone preparation contains a prasinosteroid of formula I (R is formula II, formula III, formula IV or formula V). The preparation is used by spraying or coating the peduncles or ovaries of melons with an aqueous solution containing 0.005W2ppm of a prasinosteroid of formula I or by applying a dust or wettable dust prepared by combining the steroid with a carriers and other additives and diluting the combination with water. The prasinosteroid is very useful in fruit cultivation or seed cultivation, because the hormone can give fruits of stabilized quality. Especially, it is utilized in cultivation in spring where the fruiting rate is low or in cultivation of melons which is very deformable by action of hormones.