Abstract Purpose: Due to the short-day nature of the velvet bean, which triggers flowering in the autumn with decreasing day length, its production in temperate and high-latitude regions under greenhouse conditions requires modifications in its flowering and fruiting habits. Therefore, this study aimed to optimize L-DOPA production by investigating photoperiod changes and hormonal regulation to encourage flowering and fruiting under greenhouse conditions. Research Method: Treatments included photoperiod at two levels (13-hour darkness and natural day length) as the first factor and growth regulators at seven levels (50 and 100 mg of gibberellin, 20 and 50 mg of paclobutrazol, 50 and 100 mg of cytokinin, and a control treatment) as the second factor. Findings: the effects of photoperiod, growth regulators, and their interaction were significant for all traits except for internode length. The natural light treatment resulted in a 3% delay in flowering compared to the 13-hour dark treatment, whereas the 13-hour dark treatment exhibited higher fruit weight, seed yield, and L-DOPA content (18%) compared to the natural light. Moreover, the application of 50 mg paclobutrazol reduced the days to flowering by 55 days compared to the control. On the other hand, the 50 mg paclobutrazol treatment showed significant increases in fruit weight (59%), seed yield (65%), and L-DOPA content (31%) compared to the control. Research limitations: No limitations were found. Originality/Value: Overall, extending the dark period improved velvet beans\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' yield and yield components. Furthermore, paclobutrazol enhanced yield more effectively than gibberellin and cytokinin. Based on the experiment, the best treatment for achieving maximum quantitative yield and L-DOPA content was 13-hour darkness combined with 50 mg of paclobutrazol.

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