Timing of a short-term reduction in temperature and irradiance affects growth and development of four annual bedding plants

Authors: Boldt, Jennifer; Altland, James

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2019
Publication Date: 2/1/2019
Publication URL: https://handle.nal.usda.gov/10113/6472484
Citation: Boldt, J.K., Altland, J.E. 2019. Timing of a short-term reduction in temperature and irradiance affects growth and development of four annual bedding plants. Horticulturae. 5(1):15. https://doi.org/10.3390/horticulturae5010015.
DOI: https://doi.org/10.3390/horticulturae5010015

Interpretive Summary: Greenhouse production of annual bedding plants for spring markets occurs in late winter and early spring, during the coldest and darkest months of the year. Consequently, energy costs for heating and supplemental electric lighting are a major production cost for greenhouse-grown plants. Using dynamic heating and lighting strategies, rather than maintaining static day and night set points, is one strategy to reduce energy use. We grew four species of annual bedding plants under ambient greenhouse conditions and transferred them to cool, low light conditions for a two-week period, staggered at different times during production. Flowering was delayed when the cool, low light interval occurred prior to flowering, and shoot dry mass decreased as the cool, low light interval occurred later in production. Estimated energy savings was nominal for all four species. Therefore, growers could consider using this strategy to slightly reduce overall energy use for spring production of annual bedding plants, provided cold-tolerant species are selected and an extra week of production is scheduled.

Technical Abstract: Heating and supplemental lighting are often provided during greenhouse production of spring bedding plants, but energy inputs are a major production cost. Different energy-savings strategies can be utilized, but effects on plant growth and flowering must be considered. We evaluated the impact and timing of a two-week low-energy (reduced temperature and irradiance) interval on flowering and growth of impatiens (Impatiens walleriana Hook.f. ‘Accent Orange’), pansy (Viola ×wittrockiana Gams. ‘Delta Premium Blue Blotch’), petunia (Petunia ×hybrida Hort. Vilm.-Andr. ‘Dreams Pink’), and snapdragon (Antirrhinum majus L. ‘Montego Violet’). Flowering was delayed 7 to 10 d when the low-energy exposure occurred prior to flowering. Flower number was reduced 40%-61% in impatiens, 33%-35% in petunia (low-energy weeks 5-6 and weeks 7-8, respectively), and 35% in pansy (weeks 5-6). Petunia and impatiens dry mass gradually decreased as the low-energy exposure occurred later in production; petunias were 26% (weeks 5-6) and 33% (weeks 7-8) smaller, and impatiens were 20% to 31% smaller than ambient plants. Estimated energy savings were 14% to 16% for the eight week period, but only up to 7% from transplant to flowering. Growers can consider including a two-week reduction in temperature and irradiance to reduce energy, provided an additional week of production is scheduled.