2018 ASHS Annual Conference

Reducing time to flower and improving overall crop quality by providing supplemental lighting (SL) for bedding and potted plants that are either day-neutral or facultative long-day is a proven strategy. However, there is less research on the benefit of SL on short-day plants with respect to plant morphology, growth, and time to flower delivered during both the long-day and short-day phases. Through a coordinated grower trial, winter-spring 2017-18, we investigated the effect of SL on the short-day plant Kalanchoe blossfeldiana with respect to growth and development.

Initially, during the long day grow phase SL was delivered at 85 µmol·m^-2·s^-1, provided when necessary to achieve an approximate daily light integral (DLI) of at least 10 mol·m^-2·d^-1 during an 18-h photoperiod. Depending on ambient light intensity, SL typically was utilized for an average of 14 h·d^-1. Supplemental lighting from both light-emitting diodes (LEDs) and high-pressure sodium (HPS) lamps were evaluated in separate sections of the greenhouse. The composition of wavelengths from the LEDs was approximately 19% blue, 4% green, and 77% white. At transfer from long days to short days, compactness, an important measure of plant quality, was greater among plants grown under LED SL than those grown under HPS SL.

A portion of the plants, initially grown under LEDs for the long day, 18-h photoperiod, were shifted to grow under LEDs at the same light level of 85 µmol·m^-2·s^-1 for 12-h short days. Time to flower was reduced when providing SL from LEDs during both the long days and short days phases, when compared to plants grown under HPS SL for the long-day phase alone. These findings will be integrated into a follow up study to evaluate the economic feasibility of provided SL in both the long day and short-day phases to reduce time to market for short-day plants.