Kalanchoe (Kalanchoe blossfeldiana) is a qualitative short day plant with high aesthetic value. However, its flowers are not produced when the night length is shorter than a cultivar-dependent critical value. This study investigated effect of supplementary or night interrupting (NI) low-intensity blue (B) light on plant performance and flower induction in kalanchoe ‘Rudak’. White (W) LEDs were used to provide a photosynthetic photon flux density (PPFD) of 180 μmol m−2 s−1 during the photoperiod in a closed-type plant factory with day/night temperatures of 23°C/18°C, and B LEDs were used to provide the supplementary/NI light at a 10 μmol m−2 s−1 PPFD. The control plants were exposed to a 10h short day (SD10, positive control) or 13h long day(LD13, negative control) treatment without any B light. The B light was used for 4h either 1) to supplement the W LEDs at the end of the SD10(SD10 + 4B) and LD13 (LD13 + 4B) or 2) to provide night interruption(NI) in the SD10 (SD10 + NI-4B) and LD13 (LD13 + NI-4B). The LD13+ 4B and LD13 + NI-4B significantly enhanced not only plant growth and development, but also certain monitored genes related to photosynthesis and flowering. The LD13 + NI-4B treatment resulted in plants with the greatest physiological parameters. Except in the LD13 and LD13 + NI-4B, all plants flowered. It is noteworthy that kalanchoe ‘Rudak’ flowered in the LD13 + 4B treatment and also had the greatest number of flowers, followed by the SD10 + NI-4B and SD10 + 4B. The results indicate that a 4-h supplementation of B light during the photoperiod in both the SD10 and LD13 treatments increased flower bud formation, promoted flowering, and enhanced plant performance. Especially, kalanchoe ‘Rudak’, a qualitative short-day plant, flowered in the LD13 + 4B, presenting a possibility of practically inducing flowering in long day seasons by B light application.