Determining the Effectiveness of Red and Blue Light-Emitting Diodes as Supplemental Lighting During Seedling (plug) Propagation

Annual bedding plant seedlings (plugs) are considered high-quality when they are compact, fully rooted transplants with a large stem caliper and high root dry mass. The objectives of this study were to: 1) quantify the effects of light emitting diodes (LEDs) and high pressure sodium lamps (HPS) as supplemental light sources to produce annual bedding plant seedlings; and 2) determine what red (R) to blue (B) light ratio produces the highest quality seedlings. Ten bedding plant species (Antirrhinum majus L., Begonia × semperflorens L., Catharanthus roseus L., Celosia argentea L. var. plumosa L., Impatiens walleriana Hook. f., Pelargonium × hortorum, Petunia × hybrida Vilm.-Andr., Salvia splendens Sellow ex J.A. Shultes, Tagetes patula L., and Viola × wittrockiana Gams.) were grown under 100 µmol·m^–2·s^–1 delivered from HPS lamps or LED arrays with varying proportions (%) of red:blue light (100:0, 85:15, 70:30, and HPS) with a 16-h photoperiod. Seedling of Antirrhinum, Begonia, Impatiens, Petunia, and Tagetes grown under the 85:15 light treatment were generally more compact with a larger stem caliper and higher relative chlorophyll content than plants grown under HPS lamps. For example, stem caliper increased by 13.6%, 6.5%, 3.5%, 5.1%, and 11.5 % compared to seedlings grown under HPS lamps for Antirrhinum, Begonia, Impatiens, Petunia, and Tagetes, respectively. Relative chlorophyll content of Antirrhinum and Begonia increased by 11.6% and 14.0%, respectively, compared to seedlings grown under HPS lamps. Stem length of Antirrhinum, Impatiens, and Tagetes was 5.7%, 30.6%, and 20.8% shorter, respectively, compared to seedlings grown under HPS lamps. Seedlings grown under LED light treatments generally had higher quality parameters than those grown under HPS lamps.