2019 ASHS Annual Conference

Light emitting diodes (LEDs) offer the ability to create customized light spectra for growing plants. As their efficiency continues to increase and price continues to decrease, it is likely that they will represent a larger portion of the horticultural market. This creates a need to understand how various portions of the light spectrum interact with each other to influence plant growth. We grew cucumber (Cucumis sativus) seedlings under 8 combinations of blue, green, red, and far-red light to better understand these potential interactions. When part of a broader spectrum, blue light reduced plant height resulting in more compact plants. Blue light also resulted in smaller, thicker leaves, except under monochromatic conditions. Monochromatic blue light resulted in the tallest plants with the highest shoot dry weight and leaf area and lowest compactness. Single-leaf photosynthesis measurements under ambient lighting indicated that blue light increased stomatal conductance, while red and green light resulted in higher photosynthetic rates. This increase in photosynthesis is supported by a higher shoot dry weight in treatments with red light compared to spectra lacking red light.