A high daily light integral can influence photoperiodic flowering responses in long day herbaceous ornamentals

Commercial producers of herbaceous ornamentals have reported that long-day plants sometimes flower under short-day conditions when the photosynthetic daily light integral (DLI) is high, but little research-based information available to support phenomenon. We grew seedlings tickseed (Coreopsis grandiflora), echinacea (Echinacea × hybrida), lavender (Lavandula angustifolia), lobelia (Lobelia speciosa), and salvia (Salvia longispicata farinacea) in a controlled-environment greenhouse. They were then transplanted grown photoperiods 10, 11, 12, 13, 14, or 15 h an average DLI 5.3 13.4 mol·m?2·d?1 at air temperature setpoint 20 °C. Based on flowering percentage, influenced photoperiodic responses four species. Flowering percentages tickseed, echinacea, lavender, lower low compared with high <11, <12, <13 h, respectively. Time for all species generally decreased as photoperiod increased. In addition, most had more inflorescences compact higher DLI. Under DLI, flowered tested. Salvia treatments, formed fewer leaves before ?14 other photoperiods. However, took slightly longer than 14 h. To clarify its response, we performed additional experiment following year. At germination, placed 15, 16 9 day 4-h night interruption received 9.2 mol·m?2·d?1. was delayed night-interruption treatments conclude interact influence least some has intermediate response.