One study focused on basil, demonstrating that the daily light integral (DLI)-the total amount of light received by plants over the course of a day-has a greater effect on flowering than photoperiod, or day length. Basil plants exposed to higher DLI levels flowered earlier and more consistently, indicating that light intensity and total daily exposure are critical factors for scheduling harvests and ensuring consistent flower production.
A complementary study examined seven common indoor foliage plants and their responses to different day lengths. Plant morphology, including leaf size, stem elongation, and overall biomass, was influenced by photoperiod, with longer day lengths generally promoting more compact and vigorous growth in several species. The research highlights that day length can be used strategically to shape plant form and optimize appearance for the indoor plant market.
Together, these findings emphasize that both the amount of light received daily and the duration of light exposure play important roles in plant development. For herb producers, managing light intensity can help control flowering schedules, while indoor foliage growers can use day length adjustments to influence plant morphology and marketability.
The studies provide actionable guidance for growers using controlled environments such as greenhouses, vertical farms, and indoor plant production systems. Optimizing light management can improve plant quality, reduce production time, and support more predictable scheduling for both flowering and foliage crops.
Roberto Lopes is Associate Professor and Controlled Environment/ Floriculture Extension Specialist, Department of Horticulture, Michigan State University
The full articles can be found on the ASHS HortScience electronic journal website at: https://doi.org/10.21273/HORTSCI18645-25 and https://doi.org/10.21273/HORTSCI19010-25
Established in 1903, the American Society for Horticultural Science is recognized around the world as one of the most respected and influential professional societies for horticultural scientists. ASHS is committed to promoting and encouraging national and international interest in scientific research and education in all branches of horticulture.
Comprised of thousands of members worldwide, ASHS represents a broad cross-section of the horticultural community - scientists, educators, students, landscape and turf managers, government, extension agents and industry professionals. ASHS members focus on practices and problems in horticulture: breeding, propagation, production and management, harvesting, handling and storage, processing, marketing and use of horticultural plants and products. To learn more, visit ashs.org.
