Growing High-value Ornamental Seedlings under White Light-emitting Diodes

An increasing amount of research has been conducted with monochromatic red (R) and blue (B) light-emitting diodes (LEDs) to obtain desirable plant growth responses. However, plants appear purplish under such dichromatic light, which makes detection of nutritional deficiencies and physiological disorders difficult. We grew seedlings of begonia (Begonia ×semperflorens), geranium (Pelargonium ×horturum), petunia (Petunia ×hybrida), and snapdragon (Antirrhinum majus) at 20 °C under six sole-source LED lighting treatments, many with white (W) LEDs, with an 18-h photoperiod. The following treatments delivered a PPF of 160 µmol∙m^-2∙s^-1 using B (peak= 451 nm), green (G, peak=521 nm), R (peak=660nm), and/or W (peak=552) LEDs: W₁₀₀ (100% light from W LEDs), W₇₅+ R₂₅, W₄₅+ R₅₅, W₂₅+ R₇₅, R₄₀+G₄₀+B₂₀, and R₈₅+B₁₅ (which delivered 15%, 11%, 7%, 4%, 19% and 15% B light, respectively). Compared with the R₈₅+B₁₅ treatment, preliminary results indicate that plants grown under W LED treatments were of similar or slightly taller height and had similar or slightly greater leaf area. Increases in plant height and leaf area under W light LED treatments could be attributed to a decreasing percentage of B light in the W LED treatments. The calculated yield photon flux of the W LED treatments ranged from the same to 11% less than that of R₈₅+B₁₅, but shoot dry weight was similar among treatments. We conclude that W LEDs that emit ≥15% B light can produce seedlings similar to those under dichromatic R+B light while enabling people to more easily evaluate plant growth.