Producing commercial-quality ornamental seedlings under sole-source led lighting

Light-emitting diodes (LEDs) are of increasing interest to controlled environment plant production because of their increasing energy efficiency and the ability to tailor the light spectrum to elicit desirable plant responses. Although red light plus a smaller proportion of blue light are generally considered desirable from a plant and energy efficiency perspective, little research has been published on how LEDs can be used to produce ornamental crops with desired characteristics, including compact growth of young plants. We grew seedlings of impatiens (Impatiens walleriana), salvia (Salvia splendens), petunia (Petunia x hybrida), and tomato (Solanum lycopersicum) under six sole-source LED lighting treatments that each delivered a PPF of 160 μmol∙m-2∙s-1 with an 18-h photoperiod at a constant 20°C. The following treatments were provided using blue (B, peak=446 nm), green (G, peak=516 nm), red (R, peak=634 nm), and hyper red (HR, peak=664 nm) LEDs: B25+G25+R25+HR25 (25% light from each), B50+G50, B50+R25+HR25, G50+R25+HR25, R50+HR50, and B100. A variety of growth parameters were measured included stem length, shoot fresh weight, leaf number, and leaf area. Preliminary results indicate that plants grown under treatments with ≥25% B light had 22 to 61% less leaf area and were 36 to 51% shorter than plants grown under R50+HR50. In addition, fresh weight of salvia, petunia, and tomato grown under G50+R25+HR25 or treatments with ≥25% B light was 18 to 53% less than plants grown under R50+HR50. Edema was severe in tomato under the R50+HR50 treatment and was absent under the B50+G50 treatment. We conclude that high quality ornamental seedlings can be produced under LED lighting that includes at least a minimal quantity of B or G light, and their compactness under such a light quality could reduce or eliminate the need for plant growth retardant applications.