Air Temperature Affects the Growth and Development of Cilantro, Dill, and Parsley

Culinary herbs are a popular crop for greenhouse and controlled-environment agriculture production. The yield (fresh mass) of herbs consists of foliage and, therefore, producers are interested in increasing the rate of leaf development and biomass accumulation to reduce the time to harvest and maximize yield. Our objectives were to quantify the effect of air temperature on the growth and development of cilantro (Coriandrum sativum L.; standard and heat-tolerant), dill (Anethum graveolens L.), and parsley [Petroselenium crispum (Mill.) Fuss]. Seedlings from a 288-cell plug tray were individually planted into 10-cm-diameter containers filled with a commercial soilless substrate and transferred into environmental growth chambers with one of five target air temperature air temperatures of 11, 17, 23, 29, or 35 °C. Four weeks after placing plants into temperature treatments, plant height and node number were recorded. Plants were harvested and shoot fresh mass was recorded. Shoots were then placed in a forced air drier maintained at 67 °C for 3 days then weighed and dry mass was recorded. Data were analyzed using regression analyses. For node appearance rate and fresh mass accumulation rate, optimum temperatures (T_opt) were estimated and base (T _base) temperatures were calculated. Predictive linear models were then fit to the data between T_base and T_opt, within the linear range Fresh and dry mass accumulation rate for dill, standard cilantro, and parsley exhibited similar responses to air temperature. For example, the fresh mass accumulation rate increased by 0.69, 0.57, and 0.48 g∙day^–1 as air temperature increased from 11.0 to 22.9 °C for standard cilantro, dill, and parsley, respectively, while the T_opt for fresh mass accumulation was ~26, 23, and 23 °C, respectively. Alternatively, the fresh mass accumulation for heat-tolerant cilantro increased as temperatures increased up to 29.0 °C; T_opt could not be calculated, though we speculate it is just above 29 °C, since fresh mass accumulation sharply decreased as temperatures further increased to 35.0 °C. Node appearance rate for standard cilantro, dill, and parsley followed a similar trend as fresh mass accumulation, increasing with temperature up to 22.9 °C, then decreasing as temperatures further increased, whereas node appearance rate for heat-tolerant cilantro increased by 0.61 nodes∙day^–1 as temperatures increased to 29 °C. Predictive models for node appearance rate and fresh mass accumulation may serve as a decision-support tool for predicting development and yield of cilantro cultivars, dill, and parsley in response to air temperature.