2017 ASHS Annual Conference

The adoption of Light Emitting Diodes (LEDs) as supplemental (SL) lighting in greenhouse production continues to increase. Propagators are often more capable to justify the adoption of LED technology since plugs and transplants are considered high value products and are frequently propagated during seasons with low solar daily light integrals (DLI). Commercially available LED fixtures are often equipped with blue (B) and red (R) diodes; however, new SL fixtures have few white diodes to improve plant appearance to the human eye. The objective of this research is to examine if slight changes in the SL spectrum will alter plant growth and morphology in greenhouse plug production. Petunia and geranium plugs were grown in a greenhouse until the plug stage (42 days) under 3.2 ± 0.9 mol m^-2 d^-1 solar DLI, 23.4 ± 0.36 %°C temperature, and 41.5 ± 16.4 % relative humidity. Three SL treatments were used in this experiment 1) HPS as the control, 2) an LED treatment composed of B and R diodes with 19% B and 81% R photon flux (19B:81R), and 3) an LED treatment composed of B, white (W), and R diodes with 6% B, 5% G, and 89% R photon flux (6B:5G:89R). The SL treatments provided an additional 5.8 mol m^-2 d^-1 DLI (100 μmol m^-2 s^-1 PF for 16h). Plant height, dry mass, leaf area, and plant compactness (the ratio of dry mass to height) were measured. For Geranium: plant height in 19B:81R and HPS was 35% greater than plants in 6B:5G:89R. Dry mass in HPS was 14% greater than in 6B:5G:89R. Leaf area in 19B:81R and HPS was 45% greater than in 6B:5G:89R. Compactness in 6B:5G:89R was 24% and 15% greater than in 19B:81R and HPS, respectively. For Petunia: plant height was 64% and 125% greater in 19B:81R and HPS, respectively than in 6B:5G:89R. Dry mass was 43% greater in 19B:81R and HPS than in 6B:5G:89R. Leaf area was 68% and 87% greater in 19B:81R and HPS, respectively than in 6B:5G:89R. Compactness in 6B:5G:89R was 64% greater than in HPS. In summary, a slight change in the light spectrum does affect plant growth and morphology even in greenhouse conditions were solar light already provides a balanced spectrum. Overall, plants under 19B:81R had greater growth rate and plant height than in 6B:5G:89R. However, plants in 6B:5G:89R had greater plant compactness than in 19B:81R.