Flower-bud blasting is a constraint for producing Eustoma grandiflorum so a preventative strategy is needed. Flower-bud blasting occurs under low light intensity and high fertilizer input. To gain insight into the mechanisms of flower-bud blasting, we conducted a detailed characterization of flower development under normal and blast-inducing conditions. We found that floral buds under low light intensity ceased to grow at the stamen and gynoecium differentiation stages, although sepals and petals were initiated normally. Aborted flowers rarely had normal ovules. Moreover, an expanded apical meristem was observed. These results show that the differentiation and development of reproductive organs are critically suppressed by blast-inducing conditions; however, combined application of 300 ppm benzylaminopurine and 200 ppm gibberellic acid-3 to floral buds resulted in about five-fold greater frequency of flower opening compared to controls. Blasting inhibition also resulted from excising the inflorescent branch, suggesting the decrease in assimilates in flower buds would be attributed to flower-bud blasting. Moreover, hormone application combined with excision had an additive effect for preventing flower-bud blasting, suggesting that these treatments independently inhibit flower-bud blasting. These results suggest that flower-bud blasting in Eustoma is a break in floral development around the stamen and gynoecium initiation stages and is integrally induced by the factors related to hormone biosynthesis and the decrease in assimilates.