Nighttime LED Supplemental Lighting Increases Production of Everbearing Strawberry in a Subtropical Climate

The rising demand for strawberries in tropical and subtropical regions underscores the need for effective cultivation techniques. However, the challenges posed by high temperatures in these areas have hindered successful strawberry cultivation. In this study, we investigated the impact of nighttime light-emitting diode (LED) supplemental lighting on the growth, yield, and fruit quality of three everbearing strawberry cultivars, ‘Koi-ichigo’, ‘KS33’, and ‘KS38’. They were cultivated in a controlled environment greenhouse with a crown and growth medium cooling system from August to December 2023 under high temperatures similar to tropical regions. LED lights were employed daily for 3.5–5.5 hours post-sunset to extend the day length to 16 hours per day. Under daily mean air temperatures exceeding 26°C until October, ‘Koi-ichigo’ under a natural day length underwent anthesis later than the other two cultivars. In the LED treatment, flower bud differentiation was stabilized in all cultivars due to increased photosynthetic photon flux density (PPFD). All three cultivars exhibited enhanced growth and yield under the LED treatment. Furthermore, the cultivars’ total shoot dry weight increased in response to LED supplementation. Although the LED treatment increased the number of harvested fruits, the fruit weight and soluble solid content remained comparable to those in the control. The leaf area index decreased in the LED treatment in ‘Koi-ichigo’ and ‘KS33’. At the same time, no difference in light-use efficiency was found between the control and LED treatment, and cumulative light interception surpassed that of the control in the LED treatment in all cultivars. These findings suggest that when growing everbearing strawberry cultivars in tropical and subtropical regions, nighttime LED supplemental lighting effectively stabilizes flower bud differentiation and increases the total shoot dry weight due to increased cumulative light interception, resulting in increased yield.