2019 ASHS Annual Conference

Greenhouse average daily temperature (ADT) and daily light integral (DLI) can be adjusted to improve crop timing, maximize biomass production, and increase crop quality. However, ADT and DLI models must be generated to aid growers. Therefore, our objective was to determine how ADT and DLI influence the growth and development of purple basil ‘Dark Opal’ (Ocimum basilicum), Sage ‘Extrakta’ (Salvia officinalis), and spearmint ‘Spanish’ (Mentha spicata) and the color of purple basil. Sage and purple basil seeds were sown and mint cuttings were stuck in rockwool cubes and grown in a greenhouse at 23 °C until transplant. On 19 April 2018 and 30 Oct. 2018 seedlings and liners were transplanted into one of five greenhouse compartments with ADT set points of 23, 26, 29, 32, or 35 °C. Each greenhouse contained three 1 by 2 m deep-flow hydroponic systems under 0, 30, or 50% shade cloth used to create target DLIs of 7, 9, or 12 mol·m^‒2·d^‒1. After 3, 4, or 5 weeks (mint, purple basil, and sage, respectively) leaf color (purple basil only), branch number, height, growth index, F_v/F_m, stem and leaf fresh and dry mass, and leaf area of the 4 most newly mature leaves were measured. ADT and DLI generally did not interact to influence growth or development. As DLI increased, the fresh mass of all species increased. Fresh mass of mint increased as temperature increased from 23 to 29 or 32 °C, then decreased as temperature further increased to 35 °C. Sage fresh mass decreased as temperature increased from 23 to 35 °C while purple basil had the opposite trend with fresh mass increasing with increasing temperature. However, the temperature increase that promoted purple basil growth also resulted in greener foliage color. In contrast, the higher DLIs that promoted growth resulted in less-green basil with more purple pigmentation. Additionally, leaf area generally decreased as temperatures increased from 23 to 35 °C. For example, mint, purple basil, and sage grown at 23 °C had 86, 73, and 206 % larger leaves, respectively than those grown at 35 °C. Taken together, ADT and DLI can have a large impact on growth, plant morphology, and color. The models created in this study can serve as a grower decision-support tool to improve culinary herb yields and quality.