Basil (Ocimum basilicum) and sage (Salvia officinalis) are some of the most popular fresh cut culinary herbs, but little information is available on how to cost-effectively maximize their growth and development in controlled environments. Given that cut herbs are sold by fresh mass, the goal is to maximize harvestable fresh mass, while not increasing production time, space, or energy inputs. Therefore, our objective was to determine the most effective root-zone temperature (RZT) in combination with carbon dioxide (CO2) concentration and reduced air temperature (AT) to maximize culinary herb yield. Seeds of basil ‘Genovese’ and sage were sown into 200-cell (2.5 cm × 2.5 cm) rockwool plugs and germinated for two and four weeks, respectively. Twelve seedlings of each species were transplanted into each of six 250 L, 0.9-m-wide by 1.8-m-long deep-flow hydroponic tanks among three walk-in growth chambers. Plants were grown under a total photon flux density of 260 µmol∙m–2∙s–1 for 16 h. The nutrient solution within the tanks was heated to 24, 28, or 32 °C. Additionally, AT and CO2 concentration setpoints of 20 and 23 °C and of 450 and 900 μmol∙mol‒1, respectively, were maintained for a total of 12 treatments. Basil and sage were harvested three and four weeks after transplant, respectively. Of AT, RZT, and CO2, AT was the largest contributing factor to shoot fresh mass (SFM) accumulation for both species. Increasing the air temperature from 20 to 23 °C resulted in a SFM increase of 100 and 180% in sage and basil, respectively. SFM of sage was not influenced by increasing CO2 from 450 to 900 μmol∙mol‒1 and resulted in a 12% decrease in basil SFM. However, at the high CO2 concentration, specific leaf area was 4 and 12% lower for sage and basil, respectively, resulting in greater biomass accumulation per cm2 of leaf area. RZT had no effect on basil SFM, but SFM of sage was greatest when the nutrient solution was heated to 24 and 28 °C. By maintaining an AT of 23 °C, RZT of 28 °C, and CO2 concentration of 450 μmol∙mol‒1, the SFM of both basil and sage can be maximized without further increasing RZT or CO2 concentration.
