Comparison of Supplemental Lighting Provided by High-pressure Sodium Lamps or Light-emitting Diodes for the Propagation and Finishing of Bedding Plants in a Commercial Greenhouse

Abstract

High-quality young plant production in the northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m-2·d-1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, low-profile and high-intensity light-emitting diode (LED) fixtures providing blue, red, white, and/ or far-red radiation have recently emerged as a possible alternative for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient uptake of bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures, and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. Upon germination, trays were placed in a double-poly greenhouse under a 16-h photoperiod of ambient solar light and photoperiodic lighting of 2 µmol·m–2·s–1 from compact fluorescent lamps, or SL of 70 µmol·m–2·s–1 from either HPS lamps or LED fixtures with a red:blue light ratio (%) of 90:10. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of significantly higher quality than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Similarly, SL source during propagation and finishing had little effect on flowering and finished plant quality. While these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. Additionally, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.