Blue LED Supplemental Lighting Enhances Flowering and Fruit Yield of ‘Kuemsil’ Strawberries

Strawberries ( Fragaria × ananassa Duch.) are grown in greenhouses during the winter season in Korea. Nevertheless, the light intensity in winter is lower compared with that during other seasons of the year, which can lead to inadequate photosynthesis for optimal strawberry yield. As a result, supplemental lighting is used to compensate for the lack of natural sunlight for cultivation of strawberries. However, because strawberries are classified as short-day and low-temperature plants, extending the daylength with supplemental lighting can hinder or prevent flowering. Although reports suggested that blue light can induce flowering in short-day plants, regardless of the photoperiod, few studies of strawberries have been conducted. This study was performed to assess the effects of blue light-emitting diode (LED) lights for supplemental lighting during different growth phases—after planting (AP), first flower cluster (1F), and second flower cluster (2F) phases—on flowering and fruit production of ‘Kuemsil’ strawberries. Untreated plants were used as control (CL). Strawberries were transplanted on 15 Sep 2023. The supplemental lighting treatments (blue LED; peak: 450 nm; photosynthetic photon flux density: 140 ± 5 μmol·m −2 ·s −1 ) were provided for 2 hours before sunrise and 2 hours after sunset. The photosynthetic rate of the treatment groups was significantly higher (∼331%) than that of the CL group. Vegetative growth (petiole length, leaf size, and crown diameter) was significantly greater in plants grown under supplemental lighting compared with those grown under CL conditions. Except for the AP treatment group, flowering was promoted to a greater extent in the supplemental lighting treatment groups than in the CL group. The soluble solids content was significantly higher in 1F and 2F treatments than in the other treatments.