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

Authors: CRAVER, JOSHUA - Purdue University; Boldt, Jennifer; LOPEZ, ROBERTO - Michigan State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2018
Publication Date: 1/1/2019
Citation: Craver, J.K., Boldt, J.K., Lopez, R.G. 2019. 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. HortScience. 54:52-59. https://doi.org/10.21273/HORTSCI13471-18.
DOI: https://doi.org/10.21273/HORTSCI13471-18

Interpretive Summary: he production of plants for spring bedding plant markets commonly begins during late winter and early spring, when ambient sunlight is often insufficient for high-quality growth unless supplemental lighting is provided. High-pressure sodium (HPS) lamps are the current industry standard for supplemental lighting in controlled environments, although light-emitting diodes (LEDs) are a promising alternative due to their energy-efficiency and long lifespans. Our objective was to compare the growth of six bedding plant species grown with no supplemental lighting or supplemental lighting provided by HPS or LED fixtures in a commercial greenhouse. Seedlings produced under supplemental lighting were of higher quality than those produced under no supplemental lighting. Additionally, seedlings produced under HPS or LED supplemental lighting were comparable in quality. And finally, the supplemental light source used during propagation and finishing had little effect on flowering and finished plant quality. These results confirm the benefits gained from using supplemental lighting for bedding plant production when ambient irradiance is limiting and indicate little difference in plant quality based on the supplemental light source used. With both lighting sources producing a similar finished product, growers can prioritize other factors related to supplemental lighting installations, such as energy savings, fixture price, and fixture lifespan.

Technical 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.