To investigate whether night break (i.e., the interruption of the dark period by artificial lighting) controls plant flowering sufficiently with treatment on alternate days, we compared the reproductive responses of seven horticultural crop species under a daily night-break treatment, an alternate-day treatment, and no night-break treatment during the short-daylength season. Longday crops of spinach (Spinacia oleracea), petunia (Petunia × hybrida), and godetia (Godetia cvs.) and short-day crops of cosmos (Cosmos bipinnatus), perilla (Perilla ocymoides), zinnia (Zinnia elegans), and Japanese morning glory (Pharbitis nil) were used. The night-break treatment was supplied for 2 hours starting at midnight using red light-emitting diodes. The effect of the alternate-day treatment was much smaller than the effect of the daily treatment in zinnia and Japanese morning glory
was smaller in spinach, godetia and cosmos
and was only slightly smaller in petunia. Budding in perilla was inhibited by both night-break treatments.